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US 708: Hypervelocity Star Ejected by Supernova Breaks G.S.R

  1. Mar 7, 2015 #1
    News Story
    US 708: Hypervelocity Star Ejected by Supernova Breaks Galactic Speed Record

    I recently posted about a link about a hypervelocity globular cluster. Today a story comes out discussing the fastest known hypervelocity star. SDSS J093320.86+441705.4

    It is a white dwarf star apparently ejected by a supernova.

    I used Galaxy Zoo tools to get this information and thought it might be good to share it with you, for fast reference.

    Here is the location: 09 33 20.85 +44 17 05.8
    See http://skyserver.sdss.org/dr8/en/tools/explore/obj.asp?id=1237657629516759131 and click on the spectrum, or image, or SMBAD etc. Have fun!

    SIMBAD hypervelocity star.png DR8 Hypervelocity star..png

    Last edited: Mar 7, 2015
  2. jcsd
  3. Mar 8, 2015 #2


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    1200 km/s? Someone give that star a speeding ticket!
  4. Mar 10, 2015 #3
    I read the NY Times article on this story [http://www.nytimes.com/2015/03/10/s...xy-got-an-unusual-start.html?ref=science&_r=0 ] and was a bit confused by part of its description of what took place.

    Excerpt follows:

    "Once the orbit of these two stars began to tighten, helium from the red giant was transferred to the white dwarf, according to a study published in Science. Eventually, the helium ignited, causing the white dwarf to explode."
    I get how helium gets drawn to the white dwarf. I get how the helium can achieve nuclear ignition. How does this ignition of helium cause the white dwarf to 'explode'? I could see how it might make it look like an intermittently bright nova/binary. Maybe I just am lacking knowledge of some energy thresholds? I am not taking specific issue with anything, just asking for a little guidance on the particular mechanism.

  5. Mar 10, 2015 #4


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    The accumulation of helium can indeed create normal novas, which don't blow up the entire star, but over time the mass of the white dwarf increases until it approaches the
    Chandrasekhar limit. Just prior to passing it, a runaway fusion reaction of carbon and oxygen is initiated in the core that blows the entire star apart. See the following link.

  6. Mar 10, 2015 #5
    Article read. Very enlightening :) That absolutely and clearly explained what I sought to understand.

    Thank you.

  7. Mar 11, 2015 #6
  8. Mar 11, 2015 #7


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    That star would be experiencing a time dilatory factor of almost one part in a million!

    If could go orbit that star, I'd live 5 full minutes longer than on Earth! :woot:
  9. Mar 12, 2015 #8
    But your clock on the US-708-earth would tick more slowly than here, so you'd still accumulate the same number of seconds, and your life, as you live it, would not be any longer. But of course, the supernova would have ended it anyways!

    Ignoring all that, and playing here a bit, I wonder what sky-gazers would see. Is the positional change enough to alter what constellations we would see?
  10. Mar 12, 2015 #9


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    If you're talking about going to the star, then absolutely. Constellations would change drastically.
  11. Mar 12, 2015 #10
    I almost changed the wording, afraid that would be the take.
    No... I meant to say: I wonder if the velocity of the star (and its imaginary earth) would be great enough for astronomers, living on US-708's 'earth', to notice constellations changing over time, or notice some stars (close ones) shift position in their heavens, over the lifetime of the observer. We'd spoken of what the night sky would look like like from a globular cluster. What would the night sky look like to a resident on a hypervelocity star's planet? It is just a 'for-fun' question.

    But now, as I think even more about it, if the star is outside the Milky Way, there might be few, if any constellations, as they are composed of MW stars.

    And on yet another edit.... I am not sure how many halo stars there might be out there, or how dense they'd be. Hmmmm, this is getting interesting, to me, at least.
    Last edited: Mar 12, 2015
  12. Mar 12, 2015 #11


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    I think that depends on if there are any stars close enough to be visible by the naked eye, and if those visible stars are also close enough for the motion to be noticeable. It would almost certainly be noticeable using cameras and large telescopes. Even here on Earth we have a few stars whose proper motion is noticeable over the course of a single year, Barnard's Star being the most noticeable, with more than 10 arc-seconds of proper motion per year. I could use my own personal equipment to measure its proper motion every year if I wanted to.
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