Talk:Chandrasekhar limit

Super-Chandrasekhar mass supernovae

I have changed the "Champagne Supernova" section to "Super-Chandrasekhar mass supernovae" and I expanded it by mentioning other supernovae that are believed were originated by WDs having masses greater than the Chandrasekhar mass.
RickV88 (talk) 23:03, 5 January 2012 (UTC)

Quark star

I reverted an edit that added Quark star to the lead. It's not a thing, so it does not belong in the lead.

If the Chandrasekhar limit is involved in a theory that predicts quark stars, an edit to the body of the article with a reference would be great! Johnjbarton (talk) 17:13, 15 August 2023 (UTC)

Is it useful to characterise the Chandrasekhar limit as the point at which you get runaway electron capture?

Is the Chandrasekhar limit the point beyond which electrons get captured faster than beta decay occurs in white dwarfs? MathewMunro (talk) 16:18, 6 January 2024 (UTC)

I would expect only a weak, long term relationship between Chandrasekhar's model and beta decay. The competing forces in white dwarfs are gravity vs electron degeneracy pressure. If you add an electron from beta decay you change the energics a very tiny amount. White dwarfs are stable over cosmic time; beta decay rates for Iron are extremely low. Johnjbarton (talk) 17:12, 6 January 2024 (UTC)

You wrote: 'beta decay rates for Iron are extremely low'.

Granted, but regardless of whatever the rate of beta-decay may be, would it be fair to say that due to a sufficient density and kinetic energy, white dwarfs, for example in accreting binaries, once they reach the Chandrasekhar mass limit, start capturing electrons faster than they lose them due to beta decay, and that the net electron capture is what sets off an explosive/exponential growth of electron-degeneracy pressure-loss and consequent density increase and electron capture (I'm presuming electron capture rates in white dwarfs are higher at higher densities)? MathewMunro (talk) 10:45, 7 January 2024 (UTC)

If you have a source that says that, yes. Otherwise, no. For all practical purposes the beta decay is zero as is the growth. The capture of beta decay electrons would be governed by many factors (density, radius, decay energy, electron-collision cross section) but I don't think electron degeneracy is among them. In any case I see no way that this relates to the Chandrasekhar limit since you mention accreting binaries. Johnjbarton (talk) 16:14, 7 January 2024 (UTC)

Undoubtedly the complete picture is far more complex than I comprehend, nevertheless, numerous academic authors seem to express a similar conception to mine, for example:

1. 'If the central density exceeds a critical value, electron capture can cause a dramatic reduction in the pressure of degenerate electrons and can therefore induce collapse (accretion-induced collapse [AIC]) of the white dwarf (Nomoto & Kondo 1991)' via https://iopscience.iop.org/article/10.1086/308968/fulltext/50461.text.html ('The Role of Electron Captures in Chandrasekhar-Mass Models for Type Ia Supernovae', Brachwitz, Dean, Hix, Iwamoto, Langanke, Martínez-Pinedo, Nomoto, Strayer, Thielemann and Umeda, The Astrophysical Journal, The American Astronomical Society, 2000).

2. 'If the white dwarf’s mass increases above the Chandrasekhar limit, then electron degeneracy pressure fails due to electron capture and the star collapses into a neutron star' via https://www.sciencedirect.com/science/article/abs/pii/S1387647322000203 ('Relativistic models for anisotropic compact stars: A review', Kumar and Bharti, New Astronomy Reviews, 2022).

3. 'The result of removing electrons from a completely degenerate core is contraction. Contraction increases the density and along with it, the electron-capture rates. A runaway process ensues thusly and the core of the star' via https://www.aanda.org/articles/aa/full_html/2016/09/aa28321-16/aa28321-16.html ('Do electron-capture supernovae make neutron stars?', Jones, Röpke, Pakmor, Seitenzahl, Ohlmann and Edelmann, Astronomy & Astrophysics, 2016).

4. 'Weak reactions, specifically electron-capture and beta-decay, are central to the evolution of accreting degenerate ONeMg cores. The reduction in electron fraction (and corresponding reduction in pressure) due to electron captures accelerates the contraction of the cores and the entropy generation from these electron captures can directly ignite thermonuclear reactions.' via https://academic.oup.com/mnras/article/453/2/1910/1153861 ('Thermal runaway during the evolution of ONeMg cores towards accretion-induced collapse', Schwab, Quataert and Bildsten, Monthly Notices of the Royal Astronomical Society, 2015). MathewMunro (talk) 22:35, 7 January 2024 (UTC)

The review 2) "Relativistic models for anisotropic compact stars: A review" looks great as a source. It's a review with quite a bit of introductory material and almost 400 references.

However, your quote is out of context. The context is Neutron stars created by binary accretion. The article does not contain the word "beta".

The other examples: 1) about accretion-induced collapse 3) as the title says its about electron-capture supernovae 4) does treat the competition of electron capture and beta decay in the dynamics.

In the introduction of #4 the authors explain the circumstances of their studies: various ways in which a white dwarf (WD) core can be compressed, leading to a change in the WD stability. So these are not WDs but binaries or super giant stars where the outer and inner regions are acting like a binary.

So the subject that you are describing seems to be Electron capture supernova which redirects to Supernova#Electron-capture_supernovae. Note that electron capture supernova are normally expected to be above the Chandrasekhar limit and remain speculative.

I think it would be reasonable to have a short section here on exceeding the Chandrasekhar limit by accretion based on the reivew. The key bit for this article is that a WD in the presence of other matter might get over the limit in a second try so to speak. I don't think the electron capture/beta decay competition is notable as only one theory paper mentions it. Johnjbarton (talk) 00:08, 8 January 2024 (UTC)

My point is more the common theme among them:

1. 'electron capture can cause a dramatic reduction in the pressure of degenerate electrons'.

2. 'electron degeneracy pressure fails due to electron capture'.

3. 'Contraction increases the density and along with it, the electron-capture rates'.

4. 'electron captures accelerates the contraction of the cores'.

Beta-decay is only relevant in that it is a reversal of electron capture. What's really important is NET electron capture, because electron capture that's offset by beta decay wouldn't cause the loss of pressure they all refer to. I think they all clearly mean net electron capture when they talk about electron capture even if they don't all explicitly mention beta decay as (4) does.

One important detail I missed in the initial formulation of my point was that depending on the existing composition of the star, it may either lead to direct collapse into a neutron star, or it may facilitate the fusion of heavier elements. MathewMunro (talk) 04:24, 8 January 2024 (UTC)

But my point is that none of this matters unless the WD is in a circumstance where it can acquire mass. Where are these electrons in "electron capture" coming from? They are coming from outside the WD. So I guess beta decay is a small correction. The big effect is compression from added mass. That is why all of the refs talk about accretion and only one mentions beta decay in an appendix. Johnjbarton (talk) 16:35, 8 January 2024 (UTC)

The fact that white dwarf supernovas that occur when the white dwarf crosses the Chandrasekhar limit only occurs from accretions (and mergers) is all well known and not disputed. But why does the extra mass cause a run-away chain reaction? Is it not the positive feedback of loss of electron degeneracy pressure causing higher density causing faster capture of electrons (in addition to igniting the fusion of heavier elements)? That's my (refined) point.

'The big effect is compression from added mass'. Possibly. It's certainly a major factor independent of electron capture. But the references I cited ALL mention compression from loss of electron degeneracy pressure too. And the mass gain is gradual, whereas the supernova is sudden. MathewMunro (talk) 20:09, 8 January 2024 (UTC)

I don't think the electron capture is independent of the mass addition. WD are stable. Something has to change to create collapse: added mass or remove heat. If you add mass, gravity increases (compression), changing the electron capture rate.

From the review #3:

• "If the white dwarf’s mass increases above the Chandrasekhar limit, then electron degeneracy pressure fails due to electron capture and the star collapses into a neutron star. In case of certain binary stars such as white dwarf star, mass is transferred from the companion star onto the white dwarf star, eventually pushing it over the Chandrasekhar limit. Electrons react with protons to create neutrons and thus the required pressure is not longer supplied to resist gravity, causing the star to collapse. With a further increase in density, the remaining electrons react with the protons to form more neutrons."

Since this article is about the limit, this kind of material fits well. Johnjbarton (talk) 00:17, 9 January 2024 (UTC)

'WD are stable. Something has to change to create collapse: added mass or remove heat.' - Agreed, up to the Chandrasekhar limit.

'I don't think the electron capture is independent of the mass addition.' - Your quote from reference #3 does not exactly support that. Once the WD exceeds the Chandrasekhar limit, then it no longer needs additional mass to self-generate electron capture - the Chandrasekhar limit is akin to a critical mass in an atomic bomb. Once it's exceeded, 'Electrons react with protons to create neutrons and thus the required pressure is not longer supplied to resist gravity, causing the star to collapse'.

'this kind of material [the quote from refernece #3] fits well.' - Agreed. MathewMunro (talk) 08:27, 9 January 2024 (UTC)

"Once the WD exceeds the Chandrasekhar limit then it no longer needs additional mass..." sure, that is why the limit is interesting. Johnjbarton (talk) 18:01, 9 January 2024 (UTC)

White dwarfs are usually made of carbon and oxigen

Citation: "...the stars' core compresses further allowing the helium and heavier nuclei to fuse ultimately resulting in stable iron nuclei, a process called stellar evolution. The next step depends upon the mass of the star."

This gives the impression that there is always fusion up to iron. However stellar evolution depends on the mass. In most cases, stars do not have enough mass for fusion up to iron. Wassermaus (talk) 05:47, 5 December 2024 (UTC)