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Space Science

Black Hole Found Inside Globular Cluster 73

Posted by CowboyNeal from the not-so-creamy-centers dept.
acidrain writes "Contrary to the prediction of some computer models, scientists have found a black hole resting peacefully in a dense nest of stars called a globular cluster. Previously discovered black holes are either similar in size to a large star, or super massive holes which are millions of times bigger than a star is able to remain stable. This finding indicates there may be an intermediate size range of holes residing within these star clusters."
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Black Hole Found Inside Globular Cluster More

Black Hole Found Inside Globular Cluster

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  • How many black hole discoveries do we need to announce before they no longer become news? Are the previous announcements falling into the gravity well of a collapsed star or something?

  • Previously discovered black holes are either similar in size to a large star, or super massive holes which are millions of times bigger than a star is able to remain stable.
    Er, what is measured here, when they say: "as large as a star" or even larger? I thought, black holes were singularities without any spacial extension?

    • Re: (Score:2, Informative)

      by odasnac ( 570543 )
      IANAAP, but i think it refers to the size of its event horizon [wikipedia.org]; it could refer to its mass, but from what i understand mass and event horizon size are pretty well directionally proportional.

    • Large by mass (Score:5, Informative)

      by MillionthMonkey ( 240664 ) on Saturday January 06, 2007 @01:58PM (#17489202)
      The singularity is a point but the Schwarzchild radius around it is directly proportional to mass. One earth mass is equivalent to something like a few cm of Schwarzchild radius.

      Inside the Schwarzchild radius everything falls into the hole regardless of velocity, no exceptions.
      • The singularity is a point but the Schwarzchild radius around it is directly proportional to mass. One earth mass is equivalent to something like a few cm of Schwarzchild radius.

        Inside the Schwarzchild radius everything falls into the hole regardless of velocity, no exceptions.


        aka, its event horizon
      • I just read "Schwarzchild anus" :(
      • So where is the schwarzchild radius emitted from? and why aren't we all falling into 3cm holes of doom?

        • Re: (Score:2, Informative)

          by Ambitwistor ( 1041236 )
          The Schwarzschild radius isn't "emitted" from anything. It is simply a location in space, or rather a distance that defines a location. You can define a Schwarzschild radius for any object, even yourself. A black hole (roughly speaking) is a body whose matter has all collapsed into a region smaller than its own Schwarzschild radius. The Earth is not a black hole, because its matter is not contained within a region a centimeter across. Anyway, at a distance of 1 (current) Earth radius, a cm-sized black
    • Er, what is measured here, when they say: "as large as a star" or even larger?


      I read it as mass, though I suppose it might be volume within or diameter of the event horizon. Or something else. "Size" isn't really clear here.
  • I didn't think black holes rest easily when material crosses the event horizon to be shredded violently into atomic pieces. If there was a black hole in the neighborhood, I don't think anyone would rest easily.
  • This finding indicates there may be an intermediate size range of holes

    Much like the modern workplace.

  • warning required? (Score:4, Funny)

    by PTBarnum ( 233319 ) on Saturday January 06, 2007 @02:00PM (#17489216)
    The important question is, does this black hole have a warning label?

    WARNING: do not drop spaceship keys into black hole

  • I wonder if time is dilated there... (Score:5, Interesting)

    by Progman3K ( 515744 ) on Saturday January 06, 2007 @02:23PM (#17489418)
    If you lived on a planet of the star closest to the black hole, would the passing of your time be measurably different from ours?
    • Wouldn't that at least depend on the velocity sucking my solar system into the hole (in relation to that of the observer - you get it) ?
      • The article says the black holes are "resting" inside the globular cluster, so that is my question; is/are there possibly (a) solar system(s) near the black hole that are stable?

        For that matter, if they are being pulled into the black hole, how long can a solar system keep its planet(s) orbiting in such a situation? How long could life continue in such a place?

        I'm not a physicist, but I'm sure time passes relatiely (to us) slower in such a place.
        • Just because there is a black hole in the cluster, doesn't mean that the stars are going to fall in. They could be in a stable orbit around the black hole.
          • They could be in a stable orbit around the black hole.

            Considering that the density of stars in a globular cluster and the galactic center would be quite similar, I would imagine that in time-lapse it would look something like this:
            http://video.google.com/videoplay?docid=4684576261 095940634&q=%22galactic+center%22&hl=en [google.com]

            The article says that contrary to the prediction of some computer models.... There it is, some computer models. Obviously, not everything was factored in these simulations. Also,
            • Oops, sorry about the italics, I messed up the html code. Here it goes again:

              The article says that contrary to the prediction of some computer models.... There it is, some computer models. Obviously, not everything was factored in these simulations. Also, the article says that the black hole detected is calculated to contain 400 solar masses.
              Elsewhere in this thread someone mentioned that since a black hole was detected in the second cluster they looked at, it's a fifty-fifty proposition as of now. I would
        • As far as I remmember, black hole have the same mass as the collapsing star (before starting slowly to dissipate). Thus the same gravity as the as the star would be felt at the same distance. There is albeit a difference, within the schwarschild radius, the gravity pull is enough to pull everything without possible escape even light. Normally this radius smaller than the radius of the star itself before collapsing, if the mass would be at a point. In other word if the sun was to suddenly transform in black

          • Re:Black hole do not change their mass (Score:5, Interesting)

            by SuiteSisterMary ( 123932 ) <slebrunNO@SPAMgmail.com> on Saturday January 06, 2007 @04:04PM (#17490506) Journal

            (note: this is from memory)

            Our sun is defined as 'one solar mass.'

            Very basically, a star's tendancy to collapse in on itself is countered by the fact that it's a big old nuclear fireball. As it runs out of hydrogen to burn, it starts to collapse in on itself again, until it starts burning helium. Once the helium is gone, it starts to collapse again.

            Any given star of less than 1.4 solar masses will stop collapsing and turn into a white dwarf, due to the fact that it's gravity isn't enough to overcome the repulsion of electrons. (If this white dwarf gets some new material, say, by having a red giant close enough that it can gather material from it, it will explode, giving us a supernova.)

            Any given star of greater than 1.4 solar masses but less than 3 solar masses will overcome this, but get halted by inability to squish neutrons together.

            Anything bigger than 3 solar masses will overcome neutron degeneracy, and collapse even further into a black hole.

          • Re: (Score:2)

            by sco08y ( 615665 )
            Due to Hawking radiation black holes *do* eventually lose mass and "evaporate." This happens quite quickly for small black holes and it's plausible that we could witness a nearby black hole evaporate.

        • Re:I wonder if time is dilated there... (Score:5, Funny)

          by rufty_tufty ( 888596 ) on Saturday January 06, 2007 @03:45PM (#17490316) Homepage
          "The article says the black holes are "resting" inside the globular cluster"

          Next you'll be telling me its pining for the fyords!

    • Re:I wonder if time is dilated there... (Score:5, Informative)

      by shma ( 863063 ) on Saturday January 06, 2007 @03:01PM (#17489794)
      According to General Relativity, the passage of time at a location depends on the gravitational field there. So, for instance, if the sun were to collapse into a black hole, there would be no change in the passage of time here. You would have to pass within a few Schwarzschild radii to see an effect (The Schwarzschild radius for the sun is about 3 kilometers, while Earth is 150 million km from the sum)
    • The short answer is no — if your sun were close enough to the black hole to have a significant time dilation, the tidal forces on your sun (and planet) would rip it apart.

      But at least we would get to see it in slow motion.

    • Re:I wonder if time is dilated there... (Score:4, Informative)

      by MillionthMonkey ( 240664 ) on Saturday January 06, 2007 @03:12PM (#17489926)
      If you lived on a planet of the star closest to the black hole, would the passing of your time be measurably different from ours?

      Measurably but imperceptibly different from ours. But for the planet, no different than before. The gravity along a planet's orbit would be unchanged by the star's collapse. If it survives the red giant phase or the explosion, a planet's orbit won't be expected to change. By me, anyway.

      The interesting spacetime effects that we associate with black holes take plase close to the singularity at the center, in regions of space that were formerly buried under the original star's surface. It would be hard to explain how you could find a planet bound in a stable orbit in there now. In the absence of gravity from a third body, things will either strike the singularity or take a mostly hyperbolic trajectory past it.

      And be careful what you mean when you say "would the passing of your time be measurably different from ours" because some people take that to mean that you'll look down at your watch and see the hands moving faster or slower than usual. You'll always experience proper time for your reference frame, which basically means you'll never see that. The difference is with clocks far away from the black hole, which tick more quickly than clocks closer to it.
      • Thanks, that's a really clear answer.

        When I wrote "would the passing of your time be measurably different from ours" I meant for an observer comparing both places. I should have been more precise.

        I guess the real answer (which you pointed out) is that you would have to be within the space the star itself used to occupy for relativistic effects to manifest (for an observer, again). And even then, your answer seems to say that at that point, there is no more comparison possible because no information could ex
        • Close. IANAP, but let me try.

          Those relativistic effects you're talking about would manifest if the object is massive enough, and the orbiting object is close enough. Something like that happens to mercury, but the effect is not that big.

          So, for these effects to manifest, it is not necessary for the orbiter to be inside within the space used to be occupied by the star. If a star collapses and the orbiting planet remains in the same orbit, the relativistic effects will be the same as they were (under the same
    • No different than before, because the gravitational field of a sphere outside of that sphere is equal to the graviational field of all the mass concentrated at a point. So the graviational effect of the star/black hole on the planet would be unchanged.
    • Not measurably, no.. at least, not until we send something there to measure it with.
      • Not measurably, no.. at least, not until we send something there to measure it with.


        Wouldn't the measurement results be skewed by the act of measuring?
  • "People have seen stellar-sized black holes that form from [an exploded] star, and then there are the super-massive black holes at the centres of galaxies that are millions of times the mass of our Sun - but there's nothing in between.

    That's what we've seen because that's where we've gone looking. You'd expect holes to form from supernovas, so you look at the center of planetary nebulae, where stars used to live before they exploded. You'd expect them to form at galactic centers, so you look there to find
    • If you don't look for something in a particular place, you won't find it there. This is so obvious that Heisenberg called it his Duh! Principle (little-known fact). The corollary of this principle is you won't know if something is in a particular place until you look for it there. This led Heisenberg to develop his Uncertainty Principle, and social studies has never been the same since.
  • So THAT'S where I left that thing, I'd been looking all over for it!
  • if it's in a cluster of stars that's really old, it's probably had time to suck up several and normally I don't think we'd be able to tell if say it ate five stars and got 5x bigger (well the event horizon goes out further, it doesn't actually get bigger) but if I remember correctly, gravity increases exponentially when mass is added, which is why the moon at 1/3 the size has 1/6 the gravity as earth so if it sucked up 5 stars, it would look like a couple hundred times larger and be quite noticeable.
  • "Globular clusters, which are found in the halo of a galaxy, contain considerably more stars and are much older than the less dense galactic, or open clusters, which are found in the disk." - http://en.wikipedia.org/wiki/Globular_cluster [wikipedia.org] What this makes me wonder is how the Globular Cluster, being much older than other galactic structures neither spins, nor contracts into itself. I would think that a Black Hole at the center would gobble the stars closest to it, increasing its gravitational attraction so

  • The following article has a little more info than the original (and a dodgy artist's impression of a stellar-mass black hole):

    Black hole boldly goes where no black hole has gone before [spaceflightnow.com]

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