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Space Science

Why LIGO's Black Holes Probably Didn't Come From a Single Star 46

An anonymous reader writes: Ever since LIGO first announced the direct detection of gravitational waves from two merging black holes, the physics and astronomy community has been struggling to understand an unexpected phenomenon that appears to have come along with it: a short-period gamma ray burst. Arriving just 0.4 seconds after the gravitational waves did, the Fermi satellite's detection doesn't line up with models of black hole mergers. It's thought that short-period GRBs originate from neutron star-neutron star mergers, and so seeing this has led to speculation of new physics, including from Avi Loeb at Harvard that perhaps LIGO's twin black holes came from inside the same star. However, this explanation is exceedingly unlikely, and there are a number of astrophysical explanations that don't require new physics like Loeb's explanation would.
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Why LIGO's Black Holes Probably Didn't Come From a Single Star

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  • by Framboise ( 521772 ) on Friday February 26, 2016 @06:33AM (#51590315)

    On scientific matter Forbes is really not the appropriate source.

  • by Anonymous Coward

    The last link goes to StartsWithABang.

  • Millisecond pulsars (Score:2, Informative)

    by Anonymous Coward

    There are millisecond pulsars, which are pulsars with a frequency above 1 Hz. The fastest rotating pulsar is PSR J1748-2446ad, with a frequency of 716 Hz. It's estimated that at the surface of the pulsar, at its equator, moves at 24% of the speed of light. It's pretty remarkable, but it's hardly the only millisecond pulsar. Now imagine if during the course of a star's death it became asymmetrical enough that the rotation caused it to develop a dumbbell shape. That could conceivably lead to binary neutron st

  • by Zorpheus ( 857617 ) on Friday February 26, 2016 @07:52AM (#51590497)
    It is not clear yet if there was really a Gamma Ray Burst detected. Other articles say that it was probably a fluke of the detector.
  • Why can't a single massive star collapsing into a black hole not trigger gravitational waves, why does it take two? Surely it's just the mass involved that's the important factor here?
    • Re: (Score:3, Informative)

      by Anonymous Coward

      Sources of Gravitational Waves [ligo.org]

      "In general, any acceleration that is not spherically or cylindrically symmetric will produce a gravitational wave. Consider a star that goes supernova. This explosion will produce gravitational waves if the mass is not ejected in a spherically symmetric way, although the center of mass may be in the same position before and after the explosion. Another example is a spinning star. A perfectly spherical star will not produce a gravitational wave, but a lumpy star will."

      "There

    • Why can't a single massive star collapsing into a black hole not trigger gravitational waves

      It's not just a matter of producing the waves you need to produce a large enough amplitude that you can detect it. Planets orbiting stars should in theory produce gravitational waves too but the masses and accelerations involved create such a tiny amplitude at such a low frequency that even within the solar system we can't detect that source.

    • by ceoyoyo ( 59147 ) on Friday February 26, 2016 @11:39AM (#51591589)

      The signal they detected has a quickly increasing frequency and amplitude, then a ringdown. You can't get that with a supernova, but it fits well what's expected from a couple of black holes spiraling together and merging. Thriip.

  • What effect do extremely strong gravity waves have on matter? They are saying that the energy released from this even was equal to 3 suns being converted directly into energy- that is just mind boggling...
  • by jeffb (2.718) ( 1189693 ) on Friday February 26, 2016 @08:28PM (#51595819)

    This boggles my mind, too -- that much energy radiated away as gravitational waves in a fraction of a second.

    I have some referents for electromagnetic radiation -- I know what, say, a kilojoule of light is like, and what it can do when radiated over a few seconds or a few milliseconds. But what would it be like to have your body exposed to a gravitational wave pulse carrying several kilojoules, or megajoules, or terajoules? Would you even notice?

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