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Thread: AR Scorpii

  1. #1
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    AR Scorpii

    Wikipedia article:
    https://en.wikipedia.org/wiki/AR_Scorpii
    Quote: The pulsar is about the same size as Earth.

    Is that an error? If so could someone here correct it?
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

  2. #2
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    Quote Originally Posted by Tom Mazanec View Post
    Wikipedia article:
    https://en.wikipedia.org/wiki/AR_Scorpii
    Quote: The pulsar is about the same size as Earth.

    Is that an error? If so could someone here correct it?
    In my opinion it would have been better to say that the white dwarf is about the size of the Earth. From the overall article it appears that the author is using "pulsar" to mean the whole system, not just the white dwarf.

  3. #3
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    Quote Originally Posted by Hornblower View Post
    In my opinion it would have been better to say that the white dwarf is about the size of the Earth. From the overall article it appears that the author is using "pulsar" to mean the whole system, not just the white dwarf.
    That's the problem with wikis in general - I'd guess at least two different authors, thinking about two different things, are responsible for the potential confusion.

    But, yes - someone is pointing out that a one-solar-mass white dwarf is about the size of the Earth.

    Grant Hutchison

  4. #4
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    The problem is a nonstardard use of the term "pulsar," but this problem runs throughout the short article. The author here seems to count as a "pulsar" anything that produces a periodic and spiky radio signal, but for most astronomers, a pulsar has to be a neutron star! Here we have a white dwarf and a red dwarf doing it, so this system would not normally be considered a pulsar at all, so also not a binary pulsar. But this really depends on how one likes to name objects, either by what they are are or just what observable aspects they present. There is also a common problem in astronomy vocabulary as to whether or not a binary system is a single entity or two separate entities. So when one uses the term "binary pulsar", is the "pulsar" whichever star is the neutron star, or is it both objects taken together? The nomenclature is always a bit ambiguous about that, because astronomers talk about "a binary star", and also "two stars in a binary," with no apologies to the fact that these are two very different ways to talk about a binary system.

    So I actually don't see anything particularly wrong about giving the size of "the pulsar" while meaning the star that is the source of the radio (rather than the other star that is reprocessing it, or the whole system), except that I've never seen a white dwarf counted as a "pulsar" at all. Neutron stars are so small that the nuclei, rather than just the electrons, are getting pretty relativistic, so that's more like the size of a city on Earth. The value of "binary pulsars" (and why they led to a Nobel prize) is that their gravity scale is so great it can be used to test general relativity, but a "white dwarf binary pulsar" would not be of interest in that context because the gravity is so much weaker, it probably should not even be classified similarly. Still, ambiguous terminology in astronomy is really pretty common, so we probably can't even fault the author-- it could be that as more "white dwarf pulsars" are detected, the term "pulsar" may come to no longer be restricted to neutron stars, though I think it is kind of silly to name things by what they look like instead of by what they are (welcome to astronomy nomenclature).
    Last edited by Ken G; 2019-Oct-17 at 11:41 AM.

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