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What's the most massive white dwarf in the MW?

  1. Dec 14, 2015 #1
    I'm curious. I want to model it to understand stellar evolution better. Does anyone know what the most massive single white dwarf is?
     
  2. jcsd
  3. Dec 14, 2015 #2
    We can't see every star in the galaxy so there can be no certain answer.
    However, white dwarfs do have an an upper limit to their mass known as the chandrasekar limit.
    If a white dwarf exceeds that mass it will become unstable and will detonate - a type 1a supernova.
    https://en.wikipedia.org/wiki/Chandrasekhar_limit
     
    Last edited: Dec 14, 2015
  4. Dec 14, 2015 #3
    Ok
     
  5. Dec 14, 2015 #4
    Usually this happens when a white dwarf is robbing material from a binary companion star.
    It must have happened many times in the Milky Way, though only a few such supernovae have been visible to us.
    We see this kind of supernova quite a lot when observing galaxies in general, and not just our own one.
     
  6. Dec 14, 2015 #5

    Chronos

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    RE-J0217-853 discovered by ROSAT was reported in 1998 is the current record holder with a mass of 1.35 solar [re: http://adsabs.harvard.edu/abs/1998AAS...191.1511B]. This is very near the Chandrasekhar mass limit. It is rapidly stealing mass from its companion star and is expected to reach the critical mass limit within about 4 million years. It is also a recurrent nova with a recurrence time of less than a year. White dwarfs are very difficult to detect beyond the MW for obvious reasons, although a few are known to exist. Most notable among these is probably RX J0045.4+4154 in the Andromeda Galaxy with a mass of slightly over 1.3 solar. It too is a recurrent nova feeding off a companion star with a period of right at 1 year .
     
  7. Dec 14, 2015 #6

    Chronos

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    Another factor to consider is there are two mechanisms for SN-1a production. One is the single degenerate model in which a white dwarf gains mass at the expense of a massive companion star. The other is the double degenerate model where a close binary white dwarf system suffers orbital decay via gravitational radiation [think Hulse-Taylor] and the two stars merge. The peak luminosity can obviously vary between these two models - which injects some doubt as to their reliability as standard candles. Another complication is the core composition of a white dwarf supernova progenitor. A white dwarf with an oxygen-neon core could, in theory, merely collapse to form a neutron star, or black hole as it would be unable to undergo carbon fusion. For futher discussion see http://astrobites.org/2015/04/07/super-bright-supernovae-are-single-degenerate/.
     
  8. Dec 14, 2015 #7
    Carbon and carbon/oxygen white dwarfs detonate, because there is a suitable reaction for runaway fusion explosion.

    I'm not sure this is true for oxygen/neon dwarfs and such. If runaway fusion isn't possible, then exceeding Chandrasekhar limit makes WD collapse into a neutron star, no supernova.
     
    Last edited: Dec 14, 2015
  9. Dec 14, 2015 #8
    Yes I have heard of that possibility of a direct collapse with no supernova, though am uncertain if this kind of occurance has been observed.
    I guess there would be a brief helium flash due to fusion in the envelope of material acquired from the companion, but that's about all we would see.
     
  10. Dec 15, 2015 #9
    About 1.38 times the mass of the sun is the largest for any galaxy; any bigger and it would explode.
     
  11. Dec 15, 2015 #10
    Is that value applicable to a nonrotating white dwarf, or a rapidly rotating one?
     
  12. Dec 16, 2015 #11
    Need an astrophysicist for that one, I have no idea. Is it possible for a white dwarf to not rotate? Usually highly compressed objects rotate like a bat out of hell to conserve angular momentum as it got crushed.
     
  13. Dec 18, 2015 #12

    Chronos

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    In http and //arxiv.org/abs/astro-ph/0301539, White Dwarf Rotation: Observations and Theory, the author notes:
    ..."Rotation could provide another “force” that could support the star, increasing the maximum mass for an electron degenerate configuration. Thus the hope was, in part, that by finding white dwarfs rotating at sufficiently high velocities, physics at the interface between classical and modern could be tested. One of the earliest efforts to explore this connection was by Ian Roxburgh (Roxburgh 1965), who showed that the maximum mass of a white dwarf could be increased by about 5% if rotating at near critical velocity of over 2000 km/s. As limits on rotation velocities of single white dwarfs began to be measured in the 1970s, it became apparent that they were rotating at much smaller velocities than that."
     
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