Helium flash - Revision history

JJMC89 bot III: Moving :Category:Astrophysics concepts to :Category:Concepts in astrophysics per Wikipedia:Categories for discussion/Speedy

2024-09-21T22:20:11Z

Moving Category:Astrophysics concepts to Category:Concepts in astrophysics per Wikipedia:Categories for discussion/Speedy

← Previous revision		Revision as of 22:20, 21 September 2024
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	{{DEFAULTSORT:Helium Flash}}		{{DEFAULTSORT:Helium Flash}}
	[[Category:~~Astrophysics~~ ~~concepts~~]]		[[Category:Concepts in astrophysics]]
	[[Category:Exotic matter]]		[[Category:Exotic matter]]
	[[Category:Helium]]		[[Category:Helium]]

46.18.177.138: /* References */ Category change

2024-08-23T13:11:06Z

References: Category change

← Previous revision		Revision as of 13:11, 23 August 2024
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	{{DEFAULTSORT:Helium Flash}}		{{DEFAULTSORT:Helium Flash}}
	[[Category:~~Stellar~~ ~~evolution~~]]		[[Category:Astrophysics concepts]]
⚫	[[Category:~~Astrophysics~~]]
⚫	[[Category:Nucleosynthesis]]
⚫	[[Category:~~Helium~~]]
	[[Category:Exotic matter]]		[[Category:Exotic matter]]
		⚫	[[Category:Helium]]
		⚫	[[Category:Nucleosynthesis]]
		⚫	[[Category:Stellar evolution]]

Benny the Bouncer at 00:00, 1 July 2024

2024-07-01T00:00:49Z

← Previous revision		Revision as of 00:00, 1 July 2024
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	{{short description\|Brief thermal runaway nuclear fusion in the core of low mass stars}}		{{short description\|Brief thermal runaway nuclear fusion in the core of low-mass stars}}
	[[File:Helium flash.svg\|300px\|thumb\|right\|Fusion of helium in the core of low mass stars.]]		[[File:Helium flash.svg\|300px\|thumb\|right\|Fusion of helium in the core of low-mass stars.]]
	A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.		A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low-mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.

	Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches temperature of approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.		Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches temperature of approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.

91.105.17.149: Clarify that it's a temperature

2024-05-11T10:45:06Z

Clarify that it's a temperature

← Previous revision		Revision as of 10:45, 11 May 2024
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	A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.		A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.

	Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.		Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches temperature of approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.

	However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}		However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}

Headbomb: Reverted edits by 128.135.204.242 (talk) to last version by 97.102.205.224

2024-04-22T02:38:22Z

Reverted edits by 128.135.204.242 (talk) to last version by 97.102.205.224

← Previous revision		Revision as of 02:38, 22 April 2024
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	However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}		However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}

	In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand. This consumes most of the total energy released by the helium flash,{{r\|End}} and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 20% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.<ref name=End>{{cite web \|url=http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html \|title=The End Of The Sun \|first=David \|last=Taylor \|website=[[Northwestern University]] \|quote=almost all the energy of the flash is absorbed by the titanic weight-lifting necessary to lift the core out of its white-dwarf condition.}}</ref>		In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand. This consumes most of the total energy released by the helium flash,{{r\|End}} and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 2% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.<ref name=End>{{cite web \|url=http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html \|title=The End Of The Sun \|first=David \|last=Taylor \|website=[[Northwestern University]] \|quote=almost all the energy of the flash is absorbed by the titanic weight-lifting necessary to lift the core out of its white-dwarf condition.}}</ref>

	==Red giants==		==Red giants==
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	This runaway reaction quickly climbs to about 100 billion times the star's normal energy production (for a few seconds) until the temperature increases to the point that thermal pressure again becomes dominant, eliminating the degeneracy. The core can then expand and cool down and a stable burning of helium will continue.<ref>{{Cite journal\| volume = 317\| pages = 724–732\| last = Deupree\| first = R. G.\|author2=R. K. Wallace\| title = The core helium flash and surface abundance anomalies\| journal = Astrophysical Journal\| date = 1987\|bibcode = 1987ApJ...317..724D\| doi = 10.1086/165319\| doi-access = free}}</ref>		This runaway reaction quickly climbs to about 100 billion times the star's normal energy production (for a few seconds) until the temperature increases to the point that thermal pressure again becomes dominant, eliminating the degeneracy. The core can then expand and cool down and a stable burning of helium will continue.<ref>{{Cite journal\| volume = 317\| pages = 724–732\| last = Deupree\| first = R. G.\|author2=R. K. Wallace\| title = The core helium flash and surface abundance anomalies\| journal = Astrophysical Journal\| date = 1987\|bibcode = 1987ApJ...317..724D\| doi = 10.1086/165319\| doi-access = free}}</ref>

	A star with mass greater than about 2.30 {{Solar mass}} starts to burn helium without its core becoming degenerate, and so does not exhibit this type of helium flash. In a very low-mass star (less than about 0.5 {{Solar mass}}), the core is never hot enough to ignite helium. The degenerate helium core will keep on contracting, and finally becomes a [[White dwarf#Stars with very low mass\|helium white dwarf]].		A star with mass greater than about 2.25 {{Solar mass}} starts to burn helium without its core becoming degenerate, and so does not exhibit this type of helium flash. In a very low-mass star (less than about 0.5 {{Solar mass}}), the core is never hot enough to ignite helium. The degenerate helium core will keep on contracting, and finally becomes a [[White dwarf#Stars with very low mass\|helium white dwarf]].

	The helium flash is directly observable on the surface by electromagnetic radiation. The flash occurs in the core deep inside the star, and the net effect will be that all released energy is absorbed by the entire core, causing the degenerate state to become nondegenerate. Earlier computations indicated that a nondisruptive mass loss would be possible in some cases,<ref name="Deupree1984">{{cite journal\|last1= Deupree\|first1= R. G.\|title= Two- and three-dimensional numerical simulations of the core helium flash\|journal= The Astrophysical Journal\|volume= 282\|year= 1984\|pages= 274\|doi=10.1086/162200\|bibcode= 1984ApJ...282..274D\|doi-access= free}}</ref> but later star modeling taking neutrino energy loss into account indicates no such mass loss.<ref name="Deupree1996">{{cite journal\|last1= Deupree\|first1=R. G.\|title= A Reexamination of the Core Helium Flash\|journal= The Astrophysical Journal\|volume=471\|issue= 1\|date= 1996-11-01\|pages= 377–384\|doi= 10.1086/177976\|bibcode= 1996ApJ...471..377D\|citeseerx= 10.1.1.31.44\|s2cid=15585754 }}</ref><ref>{{Cite thesis \|bibcode = 2009PhDT.........2M\|title = Multidimensional hydrodynamic simulations of the core helium flash in low-mass stars\|last1 = Mocák\|first1 = M\|year = 2009 \|type=PhD. Thesis \|publisher=Technische Universität München}}</ref>		The helium flash is not directly observable on the surface by electromagnetic radiation. The flash occurs in the core deep inside the star, and the net effect will be that all released energy is absorbed by the entire core, causing the degenerate state to become nondegenerate. Earlier computations indicated that a nondisruptive mass loss would be possible in some cases,<ref name="Deupree1984">{{cite journal\|last1= Deupree\|first1= R. G.\|title= Two- and three-dimensional numerical simulations of the core helium flash\|journal= The Astrophysical Journal\|volume= 282\|year= 1984\|pages= 274\|doi=10.1086/162200\|bibcode= 1984ApJ...282..274D\|doi-access= free}}</ref> but later star modeling taking neutrino energy loss into account indicates no such mass loss.<ref name="Deupree1996">{{cite journal\|last1= Deupree\|first1=R. G.\|title= A Reexamination of the Core Helium Flash\|journal= The Astrophysical Journal\|volume=471\|issue= 1\|date= 1996-11-01\|pages= 377–384\|doi= 10.1086/177976\|bibcode= 1996ApJ...471..377D\|citeseerx= 10.1.1.31.44\|s2cid=15585754 }}</ref><ref>{{Cite thesis \|bibcode = 2009PhDT.........2M\|title = Multidimensional hydrodynamic simulations of the core helium flash in low-mass stars\|last1 = Mocák\|first1 = M\|year = 2009 \|type=PhD. Thesis \|publisher=Technische Universität München}}</ref>

	In a one solar mass star, the helium flash is estimated to release about {{val\|5\|e=41\|ul=J}},<ref name="Edwards19690">{{cite journal \| author=Edwards, A. C.\|title= The Hydrodynamics of the Helium Flash \| journal= Monthly Notices of the Royal Astronomical Society \| date=1969 \| volume=146 \|issue= 4 \| pages=445–472 \| bibcode= 1969MNRAS.146..445E\|doi = 10.1093/mnras/146.4.445 \| doi-access= free }}</ref> or about 0.3% of the energy release of a {{val\|1.5\|e=44\|ul=J}} [[type Ia supernova]],<ref name="Khokhlov1993">{{cite journal \| author1=Khokhlov, A. \|author2=Müller, E. \|author3=Höflich, P. \| title= Light curves of Type IA supernova models with different explosion mechanisms \| journal= Astronomy and Astrophysics \| date=1993 \| volume=270 \| issue=1–2 \| pages=223–248 \| bibcode= 1993A&A...270..223K}}</ref> which is triggered by an analogous [[Carbon detonation\|ignition of carbon fusion]] in a carbon–oxygen white dwarf.		In a one solar mass star, the helium flash is estimated to release about {{val\|5\|e=41\|ul=J}},<ref name="Edwards19690">{{cite journal \| author=Edwards, A. C.\|title= The Hydrodynamics of the Helium Flash \| journal= Monthly Notices of the Royal Astronomical Society \| date=1969 \| volume=146 \|issue= 4 \| pages=445–472 \| bibcode= 1969MNRAS.146..445E\|doi = 10.1093/mnras/146.4.445 \| doi-access= free }}</ref> or about 0.3% of the energy release of a {{val\|1.5\|e=44\|ul=J}} [[type Ia supernova]],<ref name="Khokhlov1993">{{cite journal \| author1=Khokhlov, A. \|author2=Müller, E. \|author3=Höflich, P. \| title= Light curves of Type IA supernova models with different explosion mechanisms \| journal= Astronomy and Astrophysics \| date=1993 \| volume=270 \| issue=1–2 \| pages=223–248 \| bibcode= 1993A&A...270..223K}}</ref> which is triggered by an analogous [[Carbon detonation\|ignition of carbon fusion]] in a carbon–oxygen white dwarf.
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	=={{Anchor\|shell helium flash}}Shell helium flash==		=={{Anchor\|shell helium flash}}Shell helium flash==

	'''Shell helium flashes''' are a somewhat analogous but much ~~more~~ violent, nonrunaway helium ignition event, taking place in the absence of degenerate matter. They occur periodically in [[asymptotic giant branch]] stars in a shell outside the core. This is late in the life of a star in its giant phase. The star has burnt most of the helium available in the core, which is now composed of carbon and oxygen. Helium fusion continues in a thin shell around this core, but then turns off as helium becomes depleted. This allows hydrogen fusion to start in a layer above the helium layer. After enough additional helium accumulates, helium fusion is reignited, leading to a thermal pulse which eventually causes the star to expand and brighten temporarily (the pulse in luminosity is delayed because it takes a number of years for the energy from restarted helium fusion to reach the surface<ref name = "Wood"/>). Such pulses may last a few hundred years, and are thought to occur periodically every 10,~~500~~ to 100,000 years.<ref name = "Wood">{{Cite journal		'''Shell helium flashes''' are a somewhat analogous but much less violent, nonrunaway helium ignition event, taking place in the absence of degenerate matter. They occur periodically in [[asymptotic giant branch]] stars in a shell outside the core. This is late in the life of a star in its giant phase. The star has burnt most of the helium available in the core, which is now composed of carbon and oxygen. Helium fusion continues in a thin shell around this core, but then turns off as helium becomes depleted. This allows hydrogen fusion to start in a layer above the helium layer. After enough additional helium accumulates, helium fusion is reignited, leading to a thermal pulse which eventually causes the star to expand and brighten temporarily (the pulse in luminosity is delayed because it takes a number of years for the energy from restarted helium fusion to reach the surface<ref name = "Wood"/>). Such pulses may last a few hundred years, and are thought to occur periodically every 10,000 to 100,000 years.<ref name = "Wood">{{Cite journal
	\| volume = 247		\| volume = 247
	\| issue = Part 1		\| issue = Part 1

128.135.204.242 at 01:52, 22 April 2024

2024-04-22T01:52:24Z

← Previous revision		Revision as of 01:52, 22 April 2024
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	A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.		A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.

	~~High~~-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.		Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.

	However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}		However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}

	In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand. This consumes most of the total energy released by the helium flash,{{r\|End}} and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 2% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.<ref name=End>{{cite web \|url=http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html \|title=The End Of The Sun \|first=David \|last=Taylor \|website=[[Northwestern University]] \|quote=almost all the energy of the flash is absorbed by the titanic weight-lifting necessary to lift the core out of its white-dwarf condition.}}</ref>		In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand. This consumes most of the total energy released by the helium flash,{{r\|End}} and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 20% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.<ref name=End>{{cite web \|url=http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html \|title=The End Of The Sun \|first=David \|last=Taylor \|website=[[Northwestern University]] \|quote=almost all the energy of the flash is absorbed by the titanic weight-lifting necessary to lift the core out of its white-dwarf condition.}}</ref>

	==Red giants==		==Red giants==
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	This runaway reaction quickly climbs to about 100 billion times the star's normal energy production (for a few seconds) until the temperature increases to the point that thermal pressure again becomes dominant, eliminating the degeneracy. The core can then expand and cool down and a stable burning of helium will continue.<ref>{{Cite journal\| volume = 317\| pages = 724–732\| last = Deupree\| first = R. G.\|author2=R. K. Wallace\| title = The core helium flash and surface abundance anomalies\| journal = Astrophysical Journal\| date = 1987\|bibcode = 1987ApJ...317..724D\| doi = 10.1086/165319\| doi-access = free}}</ref>		This runaway reaction quickly climbs to about 100 billion times the star's normal energy production (for a few seconds) until the temperature increases to the point that thermal pressure again becomes dominant, eliminating the degeneracy. The core can then expand and cool down and a stable burning of helium will continue.<ref>{{Cite journal\| volume = 317\| pages = 724–732\| last = Deupree\| first = R. G.\|author2=R. K. Wallace\| title = The core helium flash and surface abundance anomalies\| journal = Astrophysical Journal\| date = 1987\|bibcode = 1987ApJ...317..724D\| doi = 10.1086/165319\| doi-access = free}}</ref>

	A star with mass greater than about 2.25 {{Solar mass}} starts to burn helium without its core becoming degenerate, and so does not exhibit this type of helium flash. In a very low-mass star (less than about 0.5 {{Solar mass}}), the core is never hot enough to ignite helium. The degenerate helium core will keep on contracting, and finally becomes a [[White dwarf#Stars with very low mass\|helium white dwarf]].		A star with mass greater than about 2.30 {{Solar mass}} starts to burn helium without its core becoming degenerate, and so does not exhibit this type of helium flash. In a very low-mass star (less than about 0.5 {{Solar mass}}), the core is never hot enough to ignite helium. The degenerate helium core will keep on contracting, and finally becomes a [[White dwarf#Stars with very low mass\|helium white dwarf]].

	The helium flash is ~~not~~ directly observable on the surface by electromagnetic radiation. The flash occurs in the core deep inside the star, and the net effect will be that all released energy is absorbed by the entire core, causing the degenerate state to become nondegenerate. Earlier computations indicated that a nondisruptive mass loss would be possible in some cases,<ref name="Deupree1984">{{cite journal\|last1= Deupree\|first1= R. G.\|title= Two- and three-dimensional numerical simulations of the core helium flash\|journal= The Astrophysical Journal\|volume= 282\|year= 1984\|pages= 274\|doi=10.1086/162200\|bibcode= 1984ApJ...282..274D\|doi-access= free}}</ref> but later star modeling taking neutrino energy loss into account indicates no such mass loss.<ref name="Deupree1996">{{cite journal\|last1= Deupree\|first1=R. G.\|title= A Reexamination of the Core Helium Flash\|journal= The Astrophysical Journal\|volume=471\|issue= 1\|date= 1996-11-01\|pages= 377–384\|doi= 10.1086/177976\|bibcode= 1996ApJ...471..377D\|citeseerx= 10.1.1.31.44\|s2cid=15585754 }}</ref><ref>{{Cite thesis \|bibcode = 2009PhDT.........2M\|title = Multidimensional hydrodynamic simulations of the core helium flash in low-mass stars\|last1 = Mocák\|first1 = M\|year = 2009 \|type=PhD. Thesis \|publisher=Technische Universität München}}</ref>		The helium flash is directly observable on the surface by electromagnetic radiation. The flash occurs in the core deep inside the star, and the net effect will be that all released energy is absorbed by the entire core, causing the degenerate state to become nondegenerate. Earlier computations indicated that a nondisruptive mass loss would be possible in some cases,<ref name="Deupree1984">{{cite journal\|last1= Deupree\|first1= R. G.\|title= Two- and three-dimensional numerical simulations of the core helium flash\|journal= The Astrophysical Journal\|volume= 282\|year= 1984\|pages= 274\|doi=10.1086/162200\|bibcode= 1984ApJ...282..274D\|doi-access= free}}</ref> but later star modeling taking neutrino energy loss into account indicates no such mass loss.<ref name="Deupree1996">{{cite journal\|last1= Deupree\|first1=R. G.\|title= A Reexamination of the Core Helium Flash\|journal= The Astrophysical Journal\|volume=471\|issue= 1\|date= 1996-11-01\|pages= 377–384\|doi= 10.1086/177976\|bibcode= 1996ApJ...471..377D\|citeseerx= 10.1.1.31.44\|s2cid=15585754 }}</ref><ref>{{Cite thesis \|bibcode = 2009PhDT.........2M\|title = Multidimensional hydrodynamic simulations of the core helium flash in low-mass stars\|last1 = Mocák\|first1 = M\|year = 2009 \|type=PhD. Thesis \|publisher=Technische Universität München}}</ref>

	In a one solar mass star, the helium flash is estimated to release about {{val\|5\|e=41\|ul=J}},<ref name="Edwards19690">{{cite journal \| author=Edwards, A. C.\|title= The Hydrodynamics of the Helium Flash \| journal= Monthly Notices of the Royal Astronomical Society \| date=1969 \| volume=146 \|issue= 4 \| pages=445–472 \| bibcode= 1969MNRAS.146..445E\|doi = 10.1093/mnras/146.4.445 \| doi-access= free }}</ref> or about 0.3% of the energy release of a {{val\|1.5\|e=44\|ul=J}} [[type Ia supernova]],<ref name="Khokhlov1993">{{cite journal \| author1=Khokhlov, A. \|author2=Müller, E. \|author3=Höflich, P. \| title= Light curves of Type IA supernova models with different explosion mechanisms \| journal= Astronomy and Astrophysics \| date=1993 \| volume=270 \| issue=1–2 \| pages=223–248 \| bibcode= 1993A&A...270..223K}}</ref> which is triggered by an analogous [[Carbon detonation\|ignition of carbon fusion]] in a carbon–oxygen white dwarf.		In a one solar mass star, the helium flash is estimated to release about {{val\|5\|e=41\|ul=J}},<ref name="Edwards19690">{{cite journal \| author=Edwards, A. C.\|title= The Hydrodynamics of the Helium Flash \| journal= Monthly Notices of the Royal Astronomical Society \| date=1969 \| volume=146 \|issue= 4 \| pages=445–472 \| bibcode= 1969MNRAS.146..445E\|doi = 10.1093/mnras/146.4.445 \| doi-access= free }}</ref> or about 0.3% of the energy release of a {{val\|1.5\|e=44\|ul=J}} [[type Ia supernova]],<ref name="Khokhlov1993">{{cite journal \| author1=Khokhlov, A. \|author2=Müller, E. \|author3=Höflich, P. \| title= Light curves of Type IA supernova models with different explosion mechanisms \| journal= Astronomy and Astrophysics \| date=1993 \| volume=270 \| issue=1–2 \| pages=223–248 \| bibcode= 1993A&A...270..223K}}</ref> which is triggered by an analogous [[Carbon detonation\|ignition of carbon fusion]] in a carbon–oxygen white dwarf.
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	=={{Anchor\|shell helium flash}}Shell helium flash==		=={{Anchor\|shell helium flash}}Shell helium flash==

	'''Shell helium flashes''' are a somewhat analogous but much ~~less~~ violent, nonrunaway helium ignition event, taking place in the absence of degenerate matter. They occur periodically in [[asymptotic giant branch]] stars in a shell outside the core. This is late in the life of a star in its giant phase. The star has burnt most of the helium available in the core, which is now composed of carbon and oxygen. Helium fusion continues in a thin shell around this core, but then turns off as helium becomes depleted. This allows hydrogen fusion to start in a layer above the helium layer. After enough additional helium accumulates, helium fusion is reignited, leading to a thermal pulse which eventually causes the star to expand and brighten temporarily (the pulse in luminosity is delayed because it takes a number of years for the energy from restarted helium fusion to reach the surface<ref name = "Wood"/>). Such pulses may last a few hundred years, and are thought to occur periodically every 10,~~000~~ to 100,000 years.<ref name = "Wood">{{Cite journal		'''Shell helium flashes''' are a somewhat analogous but much more violent, nonrunaway helium ignition event, taking place in the absence of degenerate matter. They occur periodically in [[asymptotic giant branch]] stars in a shell outside the core. This is late in the life of a star in its giant phase. The star has burnt most of the helium available in the core, which is now composed of carbon and oxygen. Helium fusion continues in a thin shell around this core, but then turns off as helium becomes depleted. This allows hydrogen fusion to start in a layer above the helium layer. After enough additional helium accumulates, helium fusion is reignited, leading to a thermal pulse which eventually causes the star to expand and brighten temporarily (the pulse in luminosity is delayed because it takes a number of years for the energy from restarted helium fusion to reach the surface<ref name = "Wood"/>). Such pulses may last a few hundred years, and are thought to occur periodically every 10,500 to 100,000 years.<ref name = "Wood">{{Cite journal
	\| volume = 247		\| volume = 247
	\| issue = Part 1		\| issue = Part 1

128.135.204.242 at 01:50, 22 April 2024

2024-04-22T01:50:37Z

← Previous revision		Revision as of 01:50, 22 April 2024
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	A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.		A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.

	~~Low~~-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.		High-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.

	However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}		However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}

97.102.205.224: Correct statement about duration of helium flash, with ref.

2024-03-25T05:07:10Z

Correct statement about duration of helium flash, with ref.

← Previous revision		Revision as of 05:07, 25 March 2024
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	A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.		A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.

	Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. ~~This~~ ~~increases~~ ~~the~~ ~~density~~ ~~and~~ ~~temperature~~ of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to ~~cause~~ helium fusion (or "helium burning") in the core.		Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.

	However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in ~~volume~~ of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction. This produces a flash of very intense helium fusion that lasts only a few ~~thousand years (instantaneous on astronomical scales)~~, but, in ~~a matter of~~ ~~seconds~~, ~~emits~~ energy at a rate comparable to the entire [[Milky Way]] galaxy.		However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}

	In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand, ~~however,~~ ~~consuming~~ as ~~much~~ ~~energy as~~ the total energy released by the helium flash, and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 2% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.<ref>{{cite web \|url= http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html \|title= The End Of The Sun \|first= David \|last= Taylor \|website= ~~North~~ ~~Western~~ }}</ref>		In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand. This consumes most of the total energy released by the helium flash,{{r\|End}} and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 2% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.<ref name=End>{{cite web \|url=http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html \|title=The End Of The Sun \|first=David \|last=Taylor \|website=[[Northwestern University]] \|quote=almost all the energy of the flash is absorbed by the titanic weight-lifting necessary to lift the core out of its white-dwarf condition.}}</ref>

	==Red giants==		==Red giants==

Patchworkpieces: /* Red giants */Specifying the nature of Sakurai's Object

2024-01-18T17:08:10Z

Red giants: Specifying the nature of Sakurai's Object

← Previous revision		Revision as of 17:08, 18 January 2024
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	==Red giants==		==Red giants==
	[[File:White Dwarf Resurrection.jpg\|thumb\|[[Sakurai's Object]] is a [[white dwarf]] undergoing a helium flash.<ref>{{cite web\|title=White Dwarf Resurrection\|url=http://www.eso.org/public/images/potw1531a/\|access-date=3 August 2015}}</ref>]]		[[File:White Dwarf Resurrection.jpg\|thumb\|[[Sakurai's Object]] is a [[white dwarf]] undergoing a helium shell flash.<ref>{{cite web\|title=White Dwarf Resurrection\|url=http://www.eso.org/public/images/potw1531a/\|access-date=3 August 2015}}</ref>]]
	During the [[red giant]] phase of [[stellar evolution]] in stars with less than 2.0 {{Solar mass}} the [[nuclear fusion]] of hydrogen ceases in the core as it is depleted, leaving a helium-rich core. While fusion of hydrogen continues in the star's shell causing a continuation of the accumulation of helium in the core, making the core denser, the temperature still is unable to reach the level required for helium fusion, as happens in more massive stars. Thus the thermal pressure from fusion is no longer sufficient to counter the gravitational collapse and create the [[hydrostatic equilibrium]] found in most stars. This causes the star to start contracting and increasing in temperature until it eventually becomes compressed enough for the helium core to become [[degenerate matter]]. This degeneracy pressure is finally sufficient to stop further collapse of the most central material but the rest of the core continues to contract and the temperature continues to rise until it reaches a point ({{val\|p=≈\|1\|e=8\|ul=K}}) at which the helium can ignite and start to fuse.<ref name=Hansen2004>{{cite book\|title=Stellar Interiors - Physical Principles, Structure, and Evolution\|url=https://archive.org/details/stellarinteriors00hans_446\|url-access=limited\|last1=Hansen\|first1=Carl J.\|last2=Kawaler\|first2=Steven D.\|last3=Trimble\|first3=Virginia\|isbn=978-0387200897 \|date=2004\|edition=2\|publisher=Springer\|pages=[https://archive.org/details/stellarinteriors00hans_446/page/n73 62]–5}}</ref><ref name=Seeds2012>{{cite book\|title=Foundations of Astronomy\|last1=Seeds\|first1=Michael A.\|last2=Backman\|first2=Dana E.\|pages=249–51\|date=2012\|edition=12\|publisher=[[Cengage Learning]]\|isbn=978-1133103769}}</ref><ref name=Karttunen2007>{{cite book\|title=Fundamental Astronomy\|url=https://archive.org/details/fundamentalastro00kart_346\|url-access=limited\|isbn=978-3540341437\|edition=5\|page=[https://archive.org/details/fundamentalastro00kart_346/page/n251 249]\|editor-first=Hannu\|editor-last=Karttunen\|editor2-first=Pekka\|editor2-last=Kröger\|editor3-first=Heikki\|editor3-last=Oja\|editor4-first=Markku\|editor4-last=Poutanen\|editor5-first=Karl Johan\|editor5-last=Donner\|publisher=Springer\|date=2007-06-27}}</ref>		During the [[red giant]] phase of [[stellar evolution]] in stars with less than 2.0 {{Solar mass}} the [[nuclear fusion]] of hydrogen ceases in the core as it is depleted, leaving a helium-rich core. While fusion of hydrogen continues in the star's shell causing a continuation of the accumulation of helium in the core, making the core denser, the temperature still is unable to reach the level required for helium fusion, as happens in more massive stars. Thus the thermal pressure from fusion is no longer sufficient to counter the gravitational collapse and create the [[hydrostatic equilibrium]] found in most stars. This causes the star to start contracting and increasing in temperature until it eventually becomes compressed enough for the helium core to become [[degenerate matter]]. This degeneracy pressure is finally sufficient to stop further collapse of the most central material but the rest of the core continues to contract and the temperature continues to rise until it reaches a point ({{val\|p=≈\|1\|e=8\|ul=K}}) at which the helium can ignite and start to fuse.<ref name=Hansen2004>{{cite book\|title=Stellar Interiors - Physical Principles, Structure, and Evolution\|url=https://archive.org/details/stellarinteriors00hans_446\|url-access=limited\|last1=Hansen\|first1=Carl J.\|last2=Kawaler\|first2=Steven D.\|last3=Trimble\|first3=Virginia\|isbn=978-0387200897 \|date=2004\|edition=2\|publisher=Springer\|pages=[https://archive.org/details/stellarinteriors00hans_446/page/n73 62]–5}}</ref><ref name=Seeds2012>{{cite book\|title=Foundations of Astronomy\|last1=Seeds\|first1=Michael A.\|last2=Backman\|first2=Dana E.\|pages=249–51\|date=2012\|edition=12\|publisher=[[Cengage Learning]]\|isbn=978-1133103769}}</ref><ref name=Karttunen2007>{{cite book\|title=Fundamental Astronomy\|url=https://archive.org/details/fundamentalastro00kart_346\|url-access=limited\|isbn=978-3540341437\|edition=5\|page=[https://archive.org/details/fundamentalastro00kart_346/page/n251 249]\|editor-first=Hannu\|editor-last=Karttunen\|editor2-first=Pekka\|editor2-last=Kröger\|editor3-first=Heikki\|editor3-last=Oja\|editor4-first=Markku\|editor4-last=Poutanen\|editor5-first=Karl Johan\|editor5-last=Donner\|publisher=Springer\|date=2007-06-27}}</ref>

Countercheck: delinked duplicate internal link

2023-12-23T18:43:34Z

delinked duplicate internal link

← Previous revision		Revision as of 18:43, 23 December 2023
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	The helium flash is not directly observable on the surface by electromagnetic radiation. The flash occurs in the core deep inside the star, and the net effect will be that all released energy is absorbed by the entire core, causing the degenerate state to become nondegenerate. Earlier computations indicated that a nondisruptive mass loss would be possible in some cases,<ref name="Deupree1984">{{cite journal\|last1= Deupree\|first1= R. G.\|title= Two- and three-dimensional numerical simulations of the core helium flash\|journal= The Astrophysical Journal\|volume= 282\|year= 1984\|pages= 274\|doi=10.1086/162200\|bibcode= 1984ApJ...282..274D\|doi-access= free}}</ref> but later star modeling taking neutrino energy loss into account indicates no such mass loss.<ref name="Deupree1996">{{cite journal\|last1= Deupree\|first1=R. G.\|title= A Reexamination of the Core Helium Flash\|journal= The Astrophysical Journal\|volume=471\|issue= 1\|date= 1996-11-01\|pages= 377–384\|doi= 10.1086/177976\|bibcode= 1996ApJ...471..377D\|citeseerx= 10.1.1.31.44\|s2cid=15585754 }}</ref><ref>{{Cite thesis \|bibcode = 2009PhDT.........2M\|title = Multidimensional hydrodynamic simulations of the core helium flash in low-mass stars\|last1 = Mocák\|first1 = M\|year = 2009 \|type=PhD. Thesis \|publisher=Technische Universität München}}</ref>		The helium flash is not directly observable on the surface by electromagnetic radiation. The flash occurs in the core deep inside the star, and the net effect will be that all released energy is absorbed by the entire core, causing the degenerate state to become nondegenerate. Earlier computations indicated that a nondisruptive mass loss would be possible in some cases,<ref name="Deupree1984">{{cite journal\|last1= Deupree\|first1= R. G.\|title= Two- and three-dimensional numerical simulations of the core helium flash\|journal= The Astrophysical Journal\|volume= 282\|year= 1984\|pages= 274\|doi=10.1086/162200\|bibcode= 1984ApJ...282..274D\|doi-access= free}}</ref> but later star modeling taking neutrino energy loss into account indicates no such mass loss.<ref name="Deupree1996">{{cite journal\|last1= Deupree\|first1=R. G.\|title= A Reexamination of the Core Helium Flash\|journal= The Astrophysical Journal\|volume=471\|issue= 1\|date= 1996-11-01\|pages= 377–384\|doi= 10.1086/177976\|bibcode= 1996ApJ...471..377D\|citeseerx= 10.1.1.31.44\|s2cid=15585754 }}</ref><ref>{{Cite thesis \|bibcode = 2009PhDT.........2M\|title = Multidimensional hydrodynamic simulations of the core helium flash in low-mass stars\|last1 = Mocák\|first1 = M\|year = 2009 \|type=PhD. Thesis \|publisher=Technische Universität München}}</ref>

	In a one solar mass star, the helium flash is estimated to release about {{val\|5\|e=41\|ul=J}},<ref name="Edwards19690">{{cite journal \| author=Edwards, A. C.\|title= The Hydrodynamics of the Helium Flash \| journal= Monthly Notices of the Royal Astronomical Society \| date=1969 \| volume=146 \|issue= 4 \| pages=445–472 \| bibcode= 1969MNRAS.146..445E\|doi = 10.1093/mnras/146.4.445 \| doi-access= free }}</ref> or about 0.3% of the energy release of a {{val\|1.5\|e=44\|ul=J}} [[type Ia supernova]],<ref name="Khokhlov1993">{{cite journal \| author1=Khokhlov, A. \|author2=Müller, E. \|author3=Höflich, P. \| title= Light curves of Type IA supernova models with different explosion mechanisms \| journal= Astronomy and Astrophysics \| date=1993 \| volume=270 \| issue=1–2 \| pages=223–248 \| bibcode= 1993A&A...270..223K}}</ref> which is triggered by an analogous [[Carbon detonation\|ignition of carbon fusion]] in a carbon–oxygen [[white dwarf]].		In a one solar mass star, the helium flash is estimated to release about {{val\|5\|e=41\|ul=J}},<ref name="Edwards19690">{{cite journal \| author=Edwards, A. C.\|title= The Hydrodynamics of the Helium Flash \| journal= Monthly Notices of the Royal Astronomical Society \| date=1969 \| volume=146 \|issue= 4 \| pages=445–472 \| bibcode= 1969MNRAS.146..445E\|doi = 10.1093/mnras/146.4.445 \| doi-access= free }}</ref> or about 0.3% of the energy release of a {{val\|1.5\|e=44\|ul=J}} [[type Ia supernova]],<ref name="Khokhlov1993">{{cite journal \| author1=Khokhlov, A. \|author2=Müller, E. \|author3=Höflich, P. \| title= Light curves of Type IA supernova models with different explosion mechanisms \| journal= Astronomy and Astrophysics \| date=1993 \| volume=270 \| issue=1–2 \| pages=223–248 \| bibcode= 1993A&A...270..223K}}</ref> which is triggered by an analogous [[Carbon detonation\|ignition of carbon fusion]] in a carbon–oxygen white dwarf.

	==Binary white dwarfs==		==Binary white dwarfs==

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	{{short description\|Brief thermal runaway nuclear fusion in the core of low mass stars}}		{{short description\|Brief thermal runaway nuclear fusion in the core of low-mass stars}}
	[[File:Helium flash.svg\|300px\|thumb\|right\|Fusion of helium in the core of low mass stars.]]		[[File:Helium flash.svg\|300px\|thumb\|right\|Fusion of helium in the core of low-mass stars.]]
	A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.		A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low-mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.

	Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches temperature of approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.		Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches temperature of approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.

← Previous revision		Revision as of 10:45, 11 May 2024
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	A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.		A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.

	Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.		Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches temperature of approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.

	However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}		However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}

← Previous revision		Revision as of 01:52, 22 April 2024
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	A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.		A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.

	~~High~~-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.		Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.

	However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}		However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}

	In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand. This consumes most of the total energy released by the helium flash,{{r\|End}} and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 2% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.<ref name=End>{{cite web \|url=http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html \|title=The End Of The Sun \|first=David \|last=Taylor \|website=[[Northwestern University]] \|quote=almost all the energy of the flash is absorbed by the titanic weight-lifting necessary to lift the core out of its white-dwarf condition.}}</ref>		In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand. This consumes most of the total energy released by the helium flash,{{r\|End}} and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 20% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.<ref name=End>{{cite web \|url=http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html \|title=The End Of The Sun \|first=David \|last=Taylor \|website=[[Northwestern University]] \|quote=almost all the energy of the flash is absorbed by the titanic weight-lifting necessary to lift the core out of its white-dwarf condition.}}</ref>

	==Red giants==		==Red giants==
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	This runaway reaction quickly climbs to about 100 billion times the star's normal energy production (for a few seconds) until the temperature increases to the point that thermal pressure again becomes dominant, eliminating the degeneracy. The core can then expand and cool down and a stable burning of helium will continue.<ref>{{Cite journal\| volume = 317\| pages = 724–732\| last = Deupree\| first = R. G.\|author2=R. K. Wallace\| title = The core helium flash and surface abundance anomalies\| journal = Astrophysical Journal\| date = 1987\|bibcode = 1987ApJ...317..724D\| doi = 10.1086/165319\| doi-access = free}}</ref>		This runaway reaction quickly climbs to about 100 billion times the star's normal energy production (for a few seconds) until the temperature increases to the point that thermal pressure again becomes dominant, eliminating the degeneracy. The core can then expand and cool down and a stable burning of helium will continue.<ref>{{Cite journal\| volume = 317\| pages = 724–732\| last = Deupree\| first = R. G.\|author2=R. K. Wallace\| title = The core helium flash and surface abundance anomalies\| journal = Astrophysical Journal\| date = 1987\|bibcode = 1987ApJ...317..724D\| doi = 10.1086/165319\| doi-access = free}}</ref>

	A star with mass greater than about 2.25 {{Solar mass}} starts to burn helium without its core becoming degenerate, and so does not exhibit this type of helium flash. In a very low-mass star (less than about 0.5 {{Solar mass}}), the core is never hot enough to ignite helium. The degenerate helium core will keep on contracting, and finally becomes a [[White dwarf#Stars with very low mass\|helium white dwarf]].		A star with mass greater than about 2.30 {{Solar mass}} starts to burn helium without its core becoming degenerate, and so does not exhibit this type of helium flash. In a very low-mass star (less than about 0.5 {{Solar mass}}), the core is never hot enough to ignite helium. The degenerate helium core will keep on contracting, and finally becomes a [[White dwarf#Stars with very low mass\|helium white dwarf]].

	The helium flash is ~~not~~ directly observable on the surface by electromagnetic radiation. The flash occurs in the core deep inside the star, and the net effect will be that all released energy is absorbed by the entire core, causing the degenerate state to become nondegenerate. Earlier computations indicated that a nondisruptive mass loss would be possible in some cases,<ref name="Deupree1984">{{cite journal\|last1= Deupree\|first1= R. G.\|title= Two- and three-dimensional numerical simulations of the core helium flash\|journal= The Astrophysical Journal\|volume= 282\|year= 1984\|pages= 274\|doi=10.1086/162200\|bibcode= 1984ApJ...282..274D\|doi-access= free}}</ref> but later star modeling taking neutrino energy loss into account indicates no such mass loss.<ref name="Deupree1996">{{cite journal\|last1= Deupree\|first1=R. G.\|title= A Reexamination of the Core Helium Flash\|journal= The Astrophysical Journal\|volume=471\|issue= 1\|date= 1996-11-01\|pages= 377–384\|doi= 10.1086/177976\|bibcode= 1996ApJ...471..377D\|citeseerx= 10.1.1.31.44\|s2cid=15585754 }}</ref><ref>{{Cite thesis \|bibcode = 2009PhDT.........2M\|title = Multidimensional hydrodynamic simulations of the core helium flash in low-mass stars\|last1 = Mocák\|first1 = M\|year = 2009 \|type=PhD. Thesis \|publisher=Technische Universität München}}</ref>		The helium flash is directly observable on the surface by electromagnetic radiation. The flash occurs in the core deep inside the star, and the net effect will be that all released energy is absorbed by the entire core, causing the degenerate state to become nondegenerate. Earlier computations indicated that a nondisruptive mass loss would be possible in some cases,<ref name="Deupree1984">{{cite journal\|last1= Deupree\|first1= R. G.\|title= Two- and three-dimensional numerical simulations of the core helium flash\|journal= The Astrophysical Journal\|volume= 282\|year= 1984\|pages= 274\|doi=10.1086/162200\|bibcode= 1984ApJ...282..274D\|doi-access= free}}</ref> but later star modeling taking neutrino energy loss into account indicates no such mass loss.<ref name="Deupree1996">{{cite journal\|last1= Deupree\|first1=R. G.\|title= A Reexamination of the Core Helium Flash\|journal= The Astrophysical Journal\|volume=471\|issue= 1\|date= 1996-11-01\|pages= 377–384\|doi= 10.1086/177976\|bibcode= 1996ApJ...471..377D\|citeseerx= 10.1.1.31.44\|s2cid=15585754 }}</ref><ref>{{Cite thesis \|bibcode = 2009PhDT.........2M\|title = Multidimensional hydrodynamic simulations of the core helium flash in low-mass stars\|last1 = Mocák\|first1 = M\|year = 2009 \|type=PhD. Thesis \|publisher=Technische Universität München}}</ref>

	In a one solar mass star, the helium flash is estimated to release about {{val\|5\|e=41\|ul=J}},<ref name="Edwards19690">{{cite journal \| author=Edwards, A. C.\|title= The Hydrodynamics of the Helium Flash \| journal= Monthly Notices of the Royal Astronomical Society \| date=1969 \| volume=146 \|issue= 4 \| pages=445–472 \| bibcode= 1969MNRAS.146..445E\|doi = 10.1093/mnras/146.4.445 \| doi-access= free }}</ref> or about 0.3% of the energy release of a {{val\|1.5\|e=44\|ul=J}} [[type Ia supernova]],<ref name="Khokhlov1993">{{cite journal \| author1=Khokhlov, A. \|author2=Müller, E. \|author3=Höflich, P. \| title= Light curves of Type IA supernova models with different explosion mechanisms \| journal= Astronomy and Astrophysics \| date=1993 \| volume=270 \| issue=1–2 \| pages=223–248 \| bibcode= 1993A&A...270..223K}}</ref> which is triggered by an analogous [[Carbon detonation\|ignition of carbon fusion]] in a carbon–oxygen white dwarf.		In a one solar mass star, the helium flash is estimated to release about {{val\|5\|e=41\|ul=J}},<ref name="Edwards19690">{{cite journal \| author=Edwards, A. C.\|title= The Hydrodynamics of the Helium Flash \| journal= Monthly Notices of the Royal Astronomical Society \| date=1969 \| volume=146 \|issue= 4 \| pages=445–472 \| bibcode= 1969MNRAS.146..445E\|doi = 10.1093/mnras/146.4.445 \| doi-access= free }}</ref> or about 0.3% of the energy release of a {{val\|1.5\|e=44\|ul=J}} [[type Ia supernova]],<ref name="Khokhlov1993">{{cite journal \| author1=Khokhlov, A. \|author2=Müller, E. \|author3=Höflich, P. \| title= Light curves of Type IA supernova models with different explosion mechanisms \| journal= Astronomy and Astrophysics \| date=1993 \| volume=270 \| issue=1–2 \| pages=223–248 \| bibcode= 1993A&A...270..223K}}</ref> which is triggered by an analogous [[Carbon detonation\|ignition of carbon fusion]] in a carbon–oxygen white dwarf.
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	=={{Anchor\|shell helium flash}}Shell helium flash==		=={{Anchor\|shell helium flash}}Shell helium flash==

	'''Shell helium flashes''' are a somewhat analogous but much ~~less~~ violent, nonrunaway helium ignition event, taking place in the absence of degenerate matter. They occur periodically in [[asymptotic giant branch]] stars in a shell outside the core. This is late in the life of a star in its giant phase. The star has burnt most of the helium available in the core, which is now composed of carbon and oxygen. Helium fusion continues in a thin shell around this core, but then turns off as helium becomes depleted. This allows hydrogen fusion to start in a layer above the helium layer. After enough additional helium accumulates, helium fusion is reignited, leading to a thermal pulse which eventually causes the star to expand and brighten temporarily (the pulse in luminosity is delayed because it takes a number of years for the energy from restarted helium fusion to reach the surface<ref name = "Wood"/>). Such pulses may last a few hundred years, and are thought to occur periodically every 10,~~000~~ to 100,000 years.<ref name = "Wood">{{Cite journal		'''Shell helium flashes''' are a somewhat analogous but much more violent, nonrunaway helium ignition event, taking place in the absence of degenerate matter. They occur periodically in [[asymptotic giant branch]] stars in a shell outside the core. This is late in the life of a star in its giant phase. The star has burnt most of the helium available in the core, which is now composed of carbon and oxygen. Helium fusion continues in a thin shell around this core, but then turns off as helium becomes depleted. This allows hydrogen fusion to start in a layer above the helium layer. After enough additional helium accumulates, helium fusion is reignited, leading to a thermal pulse which eventually causes the star to expand and brighten temporarily (the pulse in luminosity is delayed because it takes a number of years for the energy from restarted helium fusion to reach the surface<ref name = "Wood"/>). Such pulses may last a few hundred years, and are thought to occur periodically every 10,500 to 100,000 years.<ref name = "Wood">{{Cite journal
	\| volume = 247		\| volume = 247
	\| issue = Part 1		\| issue = Part 1

← Previous revision		Revision as of 01:50, 22 April 2024
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	A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.		A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.

	~~Low~~-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.		High-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.

	However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}		However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}

← Previous revision		Revision as of 05:07, 25 March 2024
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	A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.		A '''helium flash''' is a very brief [[thermal runaway]] [[nuclear fusion]] of large quantities of [[helium]] into [[carbon]] through the [[triple-alpha process]] in the core of low mass [[star]]s (between 0.8 [[solar mass]]es ({{Solar mass\|link=yes}}) and 2.0 {{Solar mass}}<ref>{{cite book\|type=lecture notes\|title=Stellar Structure and Evolution\|first=Onno\|last=Pols\|date=September 2009\|chapter-url=https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-url=https://web.archive.org/web/20190520071013/https://astro.uni-bonn.de/~nlanger/siu_web/ssescript/new/chapter9.pdf\|archive-date=20 May 2019\|chapter=Chapter 9: Post-main sequence evolution through helium burning}}</ref>) during their [[red giant]] phase. The [[Sun]] is predicted to experience a flash 1.2 billion years after it leaves the [[main sequence]]. A much rarer runaway helium fusion process can also occur on the surface of [[Accretion (astrophysics)\|accreting]] [[white dwarf]] stars.

	Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. ~~This~~ ~~increases~~ ~~the~~ ~~density~~ ~~and~~ ~~temperature~~ of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to ~~cause~~ helium fusion (or "helium burning") in the core.		Low-mass stars do not produce enough [[gravity\|gravitational]] pressure to initiate normal helium fusion. As the hydrogen in the core is exhausted, some of the helium left behind is instead compacted into [[degenerate matter]], supported against [[gravitational collapse]] by [[quantum mechanics\|quantum mechanical]] pressure rather than [[ideal gas law\|thermal pressure]]. Subsequent hydrogen shell fusion further increases the mass of the core until it reaches approximately 100 million [[kelvin]], which is hot enough to initiate helium fusion (or "helium burning") in the core.

	However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in ~~volume~~ of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction. This produces a flash of very intense helium fusion that lasts only a few ~~thousand years (instantaneous on astronomical scales)~~, but, in ~~a matter of~~ ~~seconds~~, ~~emits~~ energy at a rate comparable to the entire [[Milky Way]] galaxy.		However, a fundamental quality of degenerate matter is that increases in temperature do not produce an increase in the pressure of the matter until the thermal pressure becomes so very high that it exceeds degeneracy pressure. In main sequence stars, [[hydrostatic equilibrium\|thermal expansion]] regulates the core temperature, but in degenerate cores, this does not occur. Helium fusion increases the temperature, which increases the fusion rate, which further increases the temperature in a runaway reaction which quickly spans the entire core. This produces a flash of very intense helium fusion that lasts only a few minutes,{{r\|End}} but during that time, produces energy at a rate comparable to the entire [[Milky Way]] galaxy.{{r\|End}}

	In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand, ~~however,~~ ~~consuming~~ as ~~much~~ ~~energy as~~ the total energy released by the helium flash, and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 2% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.<ref>{{cite web \|url= http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html \|title= The End Of The Sun \|first= David \|last= Taylor \|website= ~~North~~ ~~Western~~ }}</ref>		In the case of normal low-mass stars, the vast energy release causes much of the core to come out of degeneracy, allowing it to thermally expand. This consumes most of the total energy released by the helium flash,{{r\|End}} and any left-over energy is absorbed into the star's upper layers. Thus the helium flash is mostly undetectable by observation, and is described solely by astrophysical models. After the core's expansion and cooling, the star's surface rapidly cools and contracts in as little as 10,000 years until it is roughly 2% of its former radius and luminosity. It is estimated that the electron-degenerate helium core weighs about 40% of the star mass and that 6% of the core is converted into carbon.<ref name=End>{{cite web \|url=http://faculty.wcas.northwestern.edu/~infocom/The%20Website/end.html \|title=The End Of The Sun \|first=David \|last=Taylor \|website=[[Northwestern University]] \|quote=almost all the energy of the flash is absorbed by the titanic weight-lifting necessary to lift the core out of its white-dwarf condition.}}</ref>

	==Red giants==		==Red giants==