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Center of the Milky Way Has Thousands of Black Holes, Study Shows (npr.org) 64

New submitter xonen shares a report from NPR: For decades, scientists have thought that black holes should sink to the center of galaxies and accumulate there. But scientists had no proof that these exotic objects had actually gathered together in the center of the Milky Way. Isolated black holes are almost impossible to detect, but black holes that have a companion -- an orbiting star -- interact with that star in ways that allow the pair to be spotted by telltale X-ray emissions. The team searched for those signals in a region stretching about three light-years out from our galaxy's central supermassive black hole. What they found there: a dozen black holes paired up with stars. Finding so many in such a small region is significant, because until now scientists have found evidence of only about five dozen black holes throughout the entire galaxy. What they've found should help theorists make better predictions about how many cosmic smashups might occur and generate detectable gravitational waves. The study has been published in the journal Nature.
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Center of the Milky Way Has Thousands of Black Holes, Study Shows

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  • Well (Score:2, Funny)

    by Anonymous Coward

    That sucks.

  • by Roger W Moore ( 538166 ) on Saturday April 07, 2018 @04:02AM (#56396847) Journal
    This is a very interesting result since it may have implications for Dark Matter. There is a gamma ray 'haze' around the central core of the galaxy that has caused some interest because without what used to be thought of as an unfeasibly large number of pulsars it would be impossible to produce from known astrophysical and so the thought was that it could be due to Dark Matter annihilations. However, if there is a far higher population of BHs than originally thought presumably this also means there should be a lot more pulsars and, if so, then this haze could be just from all these pulsars.
    • by Anonymous Coward

      Black Holes supposedly suck in everything --- will it drag the dark matter in, as well?

      • by Anonymous Coward on Saturday April 07, 2018 @07:47AM (#56397165)

        This isn't really true. Black holes do not suck things in. The natural behavior of an object interacting with a black hole is to form a stable orbit around it, just as it would around a star. To actually fall in, even on purpose, would take an enormous delta-v.

        The only way anything falls in is:
        1. If it's on a direct collision course
        2. If it enters an accretion disc, that has some sort of viscosity
        3. If it gets close enough that the gravity waves radiated from the pair are significant

    • by jfdavis668 ( 1414919 ) on Saturday April 07, 2018 @07:17AM (#56397113)
      Current observations are leaning that way. As they refined the data, it appears lumpy, not smooth. As if made by many point sources. Looks like large numbers of neutron stars, and not dark matter.
    • by HiThere ( 15173 )

      Sorry, unless you are proposing that these were primordial black holes that doesn't work, because it would throw off the Lithium balance detected in cosmic dust clouds.

      Dark matter has to either be non-baryonic, or it has to have removed itself from interactions before the first stars lit up. (I'm not sure of the details here...it could be that it needs to remove itself before symmetry breaking. Back when I was reading about this primordial black holes weren't believed in [and I'm not sure they are now] so

      • Sorry - I clearly not did explain myself well enough. The implication is that if there is a large population of pulsars then the galactic, gamma ray haze, which some are claiming is evidence of Dark Matter annihilating, could instead be explained by a very large number of pulsars in the galactic centre. The reason that pulsars have typically been excluded as an explanation is that you would need so many but the evidence here seems to suggest that there might actually be that many.

        While primordial BHs as
    • Enlighten me...or endarken me. IIUC, the mass of the galaxy can be inferred in two ways: from the number (and mass) of the visible stars it contains, and from the speed with which stars in galaxies orbit the center of the galaxy. The two numbers are an order of magnitude different, and the existence of dark matter is an inference from this difference. But if black holes were much more common in galaxies than we think, could they be the entire explanation for the discrepancy?

  • by Anonymous Coward

    It's nice to confirm that these exist, because that means that we'll get to listen to extreme mass ratio inspirals [wikipedia.org] as they fall into the central supermassive black hole. It produces a strong gravitational signal that's audible for a very long time, allowing high-precision tests of general relativity.

  • by Gravis Zero ( 934156 ) on Saturday April 07, 2018 @05:23AM (#56396975)

    You know, I told my precious star to stop hanging out with those no good singularity but did she listen? NOOOooo. She said, "he's just in my orbit" but then was consumed by him talking about "singularity this" and "singularity that" all the time. Before you know it you walk in on her are kissing that beatnik's event horizon, she goes critical and now is just like that jerk! That's when she starts merging with him in public for everyone to see! I know she has always had a warped perspective of time and space but this is on a whole new level!

    Parents, you've been warned! ;)

  • ...that carries weight.
  • Of course! That's where we keep them!
  • by Michael Woodhams ( 112247 ) on Saturday April 07, 2018 @09:58AM (#56397413) Journal

    I was having troubles seeing how this could work. Unless you are very close indeed, a 5 solar mass black hole interacts with other stars in exactly the same way as a 5 solar mass star, as the only force in action is gravity. So how can these stellar mass black holes gather near the galactic core?

    The first sentence of the paper is: "The existence of a ‘density cusp’—a localized increase in number—of stellar-mass black holes near a supermassive black hole is a fundamental prediction of galactic stellar dynamics".

    I looked up the reference for this (Bahcall and Wolf, http://adsabs.harvard.edu/doi/... [harvard.edu]). It is late at night and decades since I studied stuff like this, so mostly I'm going on that paper's abstract plus a bit of background knowledge.

    The important assumption of Bahcall and Wolf is that the stars are much less massive than the small black holes (SBH), which are much less massive than the galactic black hole (GBH). (My error was in not considering this.) Now when you have a mixture of stars and SBHs near the GBH, they are zipping around and sometimes have close encounters where they gravitationally interact. These interactions on average will shift kinetic energy from the higher energy object to the lower energy object. Due to the mass difference, this means in a SBH/star interaction, the SBH will (more often than not) transfer energy to the star, so it will slow and fall deeper into the gravitational well of the GBH.

    A good analogy is a gas with heavy and light molecules. The heavy molecules will move more slowly and at the bottom of the container the gas will be richer in heavy molecules compared to at the top of the container.

  • I know their orbit must be stable, but I'm wondering why it stay that stable.

    Couldn't one of the black hole suck something big one time, gain a lot of gravity pull of collapse the whole thing?

    • by HiThere ( 15173 )

      Stable is a relative term. It depends on how long a period of time you are considering. And near depends on what scale you are using also.

      If Einstein is correct, their orbits cannot be stable in the long term, but they may well be stable enough to last until the Milky Way merges with Andromeda.

      This is because "near" is quite relative. Here it probably means within a few hundred light years. I suppose they might be as closely packed as within a closed globular cluster, in which case they'd average only a

  • The small black hole is very close to a super massive black hole that bends everything including light. So the radiation from the small black hole will take all sorts of weird twists and turns and whatever escapes from the gravitational well of the super massive black hole will be at a strange angle. On the receiving end we see many apparent black holes, how many are real, how many are ghost images?

    I have looked through glass crystals and through small diamonds. It will show many dozen windows, but I know

    • IIUC, we don't *see* black holes, we infer their presence. Which I assume is not affected by ghost imaging.

  • Shouldn't it be more? What is the percentage of stars that produce a black hole at their deaths? Shouldn't our galaxy have thousands and thousands (or more) out of billions of star deaths?

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