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New Research Reveals Hundreds of Undiscovered Black Holes (phys.org) 75

An anonymous reader quotes a report from Phys.Org: New research by the University of Surrey published in the journal Monthly Notices of the Royal Astronomical Society has shone light on a globular cluster of stars that could host several hundred black holes, a phenomenon that until recently was thought impossible. Globular clusters are spherical collections of stars which orbit around a galactic center such as our Milky-way galaxy. Using advanced computer simulations, the team at the University of Surrey were able to see the un-see-able by mapping a globular cluster known as NGC 6101, from which the existence of black holes within the system was deduced. These black holes are a few times larger than the Sun, and form in the gravitational collapse of massive stars at the end of their lives. It was previously thought that these black holes would almost all be expelled from their parent cluster due to the effects of supernova explosion, during the death of a star. It is only as recently as 2013 that astrophysicists found individual black holes in globular clusters via rare phenomena in which a companion star donates material to the black hole. This work, which was supported by the European Research Council (ERC), has shown that in NGC 6101 there could be several hundred black holes, overturning old theories as to how black holes form.
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New Research Reveals Hundreds of Undiscovered Black Holes

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  • grit (Score:5, Funny)

    by bloodhawk ( 813939 ) on Saturday September 10, 2016 @05:40AM (#52861435)
    hundreds of black holes all at once? or is it just grit on the scanner scope?
    • Grit does not emit x ray on a constant basis. And it did, then it would isotropically do it , so we would see black hole everywhere no matter the orientation of our observation instrument ;).
      • by Anonymous Coward
        Whoosh
    • It could have been a sneeze that congealed on the scanner scope

    • Re: grit (Score:5, Funny)

      by tysonedwards ( 969693 ) on Saturday September 10, 2016 @08:04AM (#52861755)
      The thing about space - the color of space... your normal space color - is its black. And the thing about black holes, is they're black. So how are you going to see them?
      • Supposedly we could see a black hole against a nebular or, if nearby, against a starry background. Because of lensing, stars close to the limb of the hole would appear to skitter around the edge.

      • Re: grit (Score:4, Insightful)

        by ClickOnThis ( 137803 ) on Saturday September 10, 2016 @10:51AM (#52862463) Journal

        The thing about space - the color of space... your normal space color - is its black. And the thing about black holes, is they're black. So how are you going to see them?

        You "see" them by observing what they do to the stuff around them. X-ray emissions caused by charged particles being accelerated towards them. Lensing effects due to light being bent by their strong gravitational fields. Binary-star systems with an invisible companion that is too massive to be anything but a black hole. And so on.

      • Duh - with a flashlight!
  • by Anonymous Coward on Saturday September 10, 2016 @06:29AM (#52861515)
  • Did they detect the one in my wallet?

  • by TMB ( 70166 ) on Saturday September 10, 2016 @09:35AM (#52862129)

    This is definitely very cool, but "reveals" is a strong word. They've demonstrated that it's a plausible explanation for the puzzling distribution of stars in this cluster, but there are still other explanations that have not been ruled out.

    What's puzzling about the cluster is that the stars appear well-mixed -- the high mass stars follow the same distribution as the lower mass stars. That's weird because globular clusters should undergo mass segregation, where the high mass stars slowly congregate towards the center while the lower-mass stars migrate towards the outside (interestingly, this is because self-gravitating systems have negative heat capacity, which is a concept that tends to freak out non-astronomers). And we indeed see that most clusters are mass-segregated.

    So why do black holes help? They form from the most massive stars, which died early, and they end up being significantly more massive than the lower-mass stars that are left. So if there are lots of black holes, then the effect of mass segregation is to make the *black holes* congregate towards the center. In other words, mass segregation is still happening, but it's operating on black holes (which we can't see, so we don't notice its effect) instead of stars (which we can see).

    There are other ways you can explain this, though. If there's a massive-enough intermediate-mass black hole at the cluster center, that makes the process of mass segregation take longer, so it might not have had time to make any significant change. A sufficiently large fraction of binary stars within the cluster could have a similar effect (i.e. make the mass segregation timescale much longer). Or, more speculatively, you could posit that there was some dynamical event that happened to the cluster since its formation that mixed the stars, so mass segregation has not had as long to operate as we assume. So their explanation is a plausible interesting one that they have demonstrated can indeed cause the desired effect, which is really cool! But these other options also need to be investigated.

    • Good summary. You read the original paper I see. I was going to prepare a summary myself, but you beat me to it, and I don't think I can improve upon it.

    • Or, more speculatively, you could posit that there was some dynamical event that happened to the cluster since its formation that mixed the stars, so mass segregation has not had as long to operate as we assume.

      Would the accretion of the globular cluster (or mini-galaxy) into the Milky Way be an appropriate event? Or the crossings of the globular cluster through the disc-plane of the Milky Way?

      Thanks for the summary. My reading left considerable doubt over the models of the strength of "kick" that black ho

    • Could all of these black holes be the "dark matter" that they are looking for?

  • by burtosis ( 1124179 ) on Saturday September 10, 2016 @09:53AM (#52862217)
    Some novae occur though a gentle accretion process, such as a burnt out star with a companion, and some occur through expending all of thier fuel and the lack of thermal pressure causes collapse. Rarely one can be created through a merger of two stars but it's not exactly the same thing. In the first two cases it's not very clear [sciencedaily.com] what causes this but there is some evidence the process is not always symmetrical. A supernova often expends as much energy over a few hours to days as the star previously expended in its lifetime. Much of the material is blown off at up to 10% light speed. With the release of so much energy, even a very small deviation from being spherical can provide enough velocity on the black hole to exceed the pull of the gravity in these small globular clusters. So the result of the simulation is interesting and points the way forward for follow up observation.
  • Would this not instead suggest, previously undiscovered? If they have been discovered, they are not undiscovered.

We cannot command nature except by obeying her. -- Sir Francis Bacon

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