What will happen if a white dwarf star has mass higher than the Chandrasekhar limit, i.e. 1.4 times the mass of the Sun?
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2$\begingroup$ Depends. $\zeta$ Puppis has a mass that is more than 20 times the sun's mass, so there must be something more than just the "1.4 times the mass of the sun" limit you are suggesting. $\endgroup$– Kyle KanosSep 29, 2014 at 18:44
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1$\begingroup$ Changed the question to ask about a WD exceeding the Chandrasekhar limit. atprra, if you think this changes the intent of your question, please roll back the edit. $\endgroup$– Kyle OmanSep 29, 2014 at 22:31
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1$\begingroup$ @Qmechanic This question is not a duplicate (of the question indicated as such above) and should be reopened. It asks specifically what happens to a white dwarf as its mass increases. The answer would comprise of a discussion of GR instabilities, electron capture instabilities and the production of type Ia SNe. $\endgroup$– ProfRobOct 13, 2014 at 21:50
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$\begingroup$ Hi @Rob Jeffries. I'm a bit tired now. Could I ask you to lobby for a reopening in our chat room? $\endgroup$– Qmechanic ♦Oct 13, 2014 at 21:54
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$\begingroup$ see also astronomy.stackexchange.com/a/14747/2531 $\endgroup$– ProfRobOct 15, 2021 at 7:30
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3 Answers
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Let's assume you just add mass to a cold, completely degenerate white dwarf.
Now one possibility is that the added matter undergoes fusion reactions on the surface, resulting in mass loss and a Nova outburst. But let's ignore this and assume the added matter "sticks".
If we consider an ideal electron-degenerate carbon white dwarf, then its " Chandrasekhar limit" is either governed by a GR instability at finite density, or by the initiation of electron-capture reactions onto carbon nuclei. The two have very similar density thresholds $(\sim 4\times 10^{13}$ kg/m$^3$), and this sets the real Chandrasekhar limit to be about $1.39 M_{\odot}$.
If the WD mass exceeds this, then either it will collapse and initiate electron capture, or electron-capture will initiate a collapse, since electrons are being removed from the gas and it is the pressure of those electrons that prop the star up.
The final outcome will probably be a type Ia supernova, where the density and temperature in the collapsing WD become high enough to ignite carbon fusion reactions. Because the material is degenerate and degeneracy pressure does not depend on temperature, the reactions can "runaway". The amount of energy released when fusing the carbon exceeds the gravitational binding energy of the white dwarf and the whole thing explodes leaving no remnant (a back-of-the-envelope calculation is here).
An alternative idea is that electron capture proceeds so rapidly that there is insufficient time for enough energy to be liberated by carbon fusion to blow the star part (e.g. Metzger et al. 2009). The outcome then will most likely be an "underpowered" supernova that leaves behind a neutron star remnant. This is known as "accretion-induced collapse". This scenario is more likely for a white dwarfs that exceed the mass limit by merger with another white dwarf or by accretion onto a white dwarf with a greater oxygen content, because oxygen is harder to ignite than carbon (e.g. Tauris et al. 2013).
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According to Wikipedia
The Chandrasekhar limit is the maximum mass of a stable white dwarf star. The limit was first published by Wilhelm Anderson and E. C. Stoner, and was named after Subrahmanyan Chandrasekhar, the Indian-American astrophysicist who improved upon the accuracy of the calculation in 1930, at the age of 19.
White dwarfs with masses greater than the limit undergo further gravitational collapse, evolving into a different type of stellar remnant, such as a neutron star or black hole.
Also read this nice lecture.
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$\begingroup$ Whilst this may be possible, the more usual outcome is likely to be a type Ia supernova and no remnant. $\endgroup$– ProfRobSep 12, 2015 at 19:57
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Above the Chandrashekhar limit you would obtain a neutron star: https://en.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E2%80%93Volkoff_limit
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$\begingroup$ Zeta Puppis is an extreme blue supergiant, one of the most luminous stars in the Milky Way. That is a star with 22.5 solar masses.. not a white dwarf or a neutron star but a type O star. $\endgroup$– JasperSep 29, 2014 at 18:45
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2$\begingroup$ I know what it is, but your answer says that anything above the Chandrasekhar limit would make a neutron star which is demonstrably false. The question also says nothing of white dwarfs or neutron stars or anything, it just says "a body." $\endgroup$ Sep 29, 2014 at 18:47
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2$\begingroup$ @Kyle: if you are not satisfied with this reasoning, you might also want to change the wikipedia page: en.wikipedia.org/wiki/Chandrasekhar_limit $\endgroup$– JasperSep 29, 2014 at 18:49
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1$\begingroup$ My issue is with your false statement; you claim that any object with a mass above the Chandrasekhar limit would become a neutron star, this is observably false. The Wikipedia article covers some details that are necessary for your answer to be worth anything (and your comments touch upon the details). $\endgroup$ Sep 29, 2014 at 18:54