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In my astronomy class I learned that a only low-mass stars (< 0.5 Msun) will contract, and then become degenerate, until it is a white dwarf. However, we also learned about the Chandrasekhar limit, which states white dwarfs have a maximum mass of 1.4 Msun.

If the starting star has less than 0.5 Msun, how does the resulting white-dwarf reach up to 1.4 Msun?

Am I perhaps wrong in my assumption that the mass of the resulting white-dwarf depends on the mass of the original star?

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closed as off-topic by Donald.McLean Mar 14 '16 at 13:23

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  • $\begingroup$ Nb You have put an identical question on Physics SE, which I have answered. This question should be closed. $\endgroup$ – Rob Jeffries Mar 14 '16 at 7:11
  • $\begingroup$ See identical duplicate physics.stackexchange.com/questions/243298/… $\endgroup$ – Rob Jeffries Mar 14 '16 at 7:14
  • $\begingroup$ This question has been posted on multiple sites. Cross-posting is strongly discouraged; see the help center and community FAQ for more information. $\endgroup$ – Donald.McLean Mar 14 '16 at 13:23
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    $\begingroup$ I don't think this question should be closed. Ignoring the cross-posting, this question is definitely about astronomy and is not off-topic. I would say better suited to here than Physics SE! $\endgroup$ – FJC Mar 14 '16 at 13:42
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    $\begingroup$ @FJC For questions that are on-topic on two sites, the user gets to pick. By accepting the answer on Physics, they have de-facto picked that site. $\endgroup$ – Donald.McLean Mar 14 '16 at 13:52
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You were taught wrong. Stars of up to about 8 solar masses will end up as white dwarfs. But it is only their cores that become degenerate and end up as the white dwarf. The rest of the envelope is lost during the giant phase due to a dense wind.

There is a non-linear, but probably monotonic, relation between the initial progenitor and final white dwarf masses (see below, from Kalirai 2013) - the Sun will likely end as a 0.5 solar mass white dwarf, but in normal stellar evolution, degenerate white dwarf stars can only be produced up to about 1.25 solar masses by the most massive progenitors. Any more massive than this and it is likely that the core does not become degenerate before igniting and burning through the heavier nuclear fuels. The most massive, probably single, white dwarf known is "WD 33" in the cluster NGC 2099 and has a mass of $1.28^{+0.05}_{-0.08}\ M_{\odot}$, is likely made of an O/Ne mixture, and had an estimated progenitor mass on the main sequence of $>3.5\ M_{\odot}$ (Cummings et al. (2016).

In order to get a more massive white dwarf, up to the Chandrasekhar mass (about 1.38 solar masses for a C/O or O/Ne white dwarf in general relativity), it almost certainly needs to accrete mass from a close binary companion or be the result of some sort of merger.

This is the leading candidate to explain type Ia supernova.

Initial final mass relation

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From these 2 sites: whitedwarf.org and imagine.gsfc.nasa.gov both states that stars less than 8 times the solar masses would eventually become a white a white dwarf. So, depending on the mass of the star, a white dwarf having 1.4 solar masses is possible.

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  • $\begingroup$ According to current models and empirical measurements it does not appear to be possible to produce white dwarfs more massive than 1.25 solar masses through normal, single star evolution. $\endgroup$ – Rob Jeffries Mar 15 '16 at 7:04

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