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Space Science

Spinning Black Hole's Edge Rotates At Nearly the Speed of Light 227

Posted by Soulskill
from the you-must-be-this-tall-to-ride-the-black-hole dept.
astroengine writes "Astronomers have directly measured the spin of a black hole for the first time by detecting the mind-bending relativistic effects that warp space-time at the very edge of its event horizon. By monitoring X-ray emissions from iron ions (iron atoms with some electrons missing) trapped in the black hole's accretion disk, the rapidly-rotating inner edge of the disk of hot material has provided direct information about how fast the black hole is spinning. Astronomers used NASA's Nuclear Spectroscopic Telescope Array (NuSTAR) — that was launched into Earth orbit in June 2012 — and the European observatory XMM-Newton measured X-ray radiation as a tool to directly infer the spin of NGC 1365's black hole. 'What excites me is the fact that we are able to do this for the very massive black holes at the centers of galaxies but we can also make the same measurement for black holes in our galaxy ... black holes that resulted from the explosion of a star ... The fact we can extend this from billions of solar masses to 10 solar masses is pretty cool,' Fiona Harrison, professor of physics and astronomy at the California Institute of Technology, Pasadena, Calif., and principal investigator of the NuSTAR mission, told Discovery News."
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Spinning Black Hole's Edge Rotates At Nearly the Speed of Light

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  • by Anonymous Coward on Wednesday February 27, 2013 @04:28PM (#43027803)

    i love how this summary explains what an ion is, but assumes i know the definitions of black hole, x-ray, and solar mass. great writing, folks!

    • Ion not an astrophysicist, but ... I did like the way they explained angular momentum. I think everyone sort of knows what a black hole is by now; who hasn't had an x-ray? and mass is just high school chemistry, if not junior high.
      • by vux984 (928602) on Wednesday February 27, 2013 @05:20PM (#43028297)

        I think everyone sort of knows what a black hole is by now; who hasn't had an x-ray? and mass is just high school chemistry, if not junior high.

        Ions are elementary chemistry as well, and are covered early on in school, grade 7 or 8 at the latest I think. Acids and bases, potato batteries, etc.

        And knowing what an "x-ray exam" is doesn't tell you anything about what an x-ray actually is, nor what they are doing near black holes.

      • You're obviously not from the deep southern United States.

        Mass is at least college level, maybe graduate level.

        • Re: (Score:3, Funny)

          by Anonymous Coward

          No no, a mass is what happens in a Church you heathen.

      • by Nyder (754090)

        Ion not an astrophysicist, but ... I did like the way they explained angular momentum. I think everyone sort of knows what a black hole is by now; who hasn't had an x-ray? and mass is just high school chemistry, if not junior high.

        Mass is chemistry? damn public school education.

    • Re: (Score:2, Funny)

      by oodaloop (1229816)
      Of course, it doesn't define accretion, earth, relativistic, radiation, mass, electron, or spin either. If you don't know anything about physics, go post on 4chan or something.
      • by nedlohs (1335013) on Wednesday February 27, 2013 @05:15PM (#43028259)

        That's the point. It wastes a bunch of words explaining what an ion is.

        If you don't know what an ion is the rest of the words are going to make any sense anyway.

    • by alen (225700)

      didn't graduate high school

      or did you go to school before the big bang?

    • Re: (Score:2, Interesting)

      by Anonymous Coward

      i love how this summary explains what an ion is, but assumes i know the definitions of black hole, x-ray, and solar mass. great writing, folks!

      I love how that part of the summary is plagiarized from the page one of the first article linked and the link takes you to page two!

    • by Idbar (1034346)
      It seems like you got caught in the mind-bending relativistic effects of the summary.
    • by 140Mandak262Jamuna (970587) on Wednesday February 27, 2013 @05:02PM (#43028135) Journal
      Till I read the summary I thought ion is a iron with the letter r removed. Now I know what is removed is not r but electrons. Got it.
    • by K. S. Kyosuke (729550) on Wednesday February 27, 2013 @05:12PM (#43028223)

      i love how this summary explains what an ion is, but assumes i know the definitions of black hole, x-ray, and solar mass. great writing, folks!

      You forgot "space-time", "event horizon" and "accretion disk".

      I'm also astounded by the discovery of black holes resulting from an explosion of a star. So far I thought that a black hole is a result of an implosion of a star. This is a major new discovery!

      • Re: (Score:3, Informative)

        by voidphoenix (710468)
        It's both, iirc. Star goes supernova, the remnants collapse into a black hole.
      • by smpoole7 (1467717) on Wednesday February 27, 2013 @06:43PM (#43028861) Homepage

        > I'm also astounded by the discovery of black holes resulting from an explosion of a star.

        Really massive stars (greater that 250 solar masses -- i.e., 250 times as massive as our own Sun) most assuredly do explode, and *very* violently, leaving behind a black hole. It's believed that this is a key source for gamma ray burst events. It's also thought that many of the first stars in the universe, not long after the Big Bang, exploded this way, spewing jets of metals at relativistic speeds.

        To be fair to you, it's now known that there are actually several different types of supernova. Some core collapses do occur without a big earthshattering "kaboom." The really massive stars explode due to photodisintegration, and result in a hypernova -- a ridiculously intense, you-don't-want-to-be-within-a-hundred-light-years kind of thingie. :)

        http://en.wikipedia.org/wiki/Photodisintegration [wikipedia.org]

        http://en.wikipedia.org/wiki/Supernova [wikipedia.org]

    • by Artraze (600366)

      And relativistic effects and thus why any of this is even mildly interesting. I guess they explained accretion disc too, though, so that's something.

      But beyond that, what I find most awesome about it is that it's completely unnecessary for understanding anything about this. They could've said "X-ray emissions from walruses (large flippered marine mammals) trapped in the black hole's accretion disk" and it wouldn't have really made any difference to 99+% of the audience, aside from causing us to wonder why

    • by PhxBlue (562201)
      Probably so folks wouldn't think it was a typo, e.g., iron iron.
  • by ShanghaiBill (739463) * on Wednesday February 27, 2013 @04:37PM (#43027887)

    Have they shown that the black hole is rotating near c, or just that the accretion disk is rotating near c at the event horizon? The accretion disk and the black hole are not necessarily spinning in sync. If they mean the accretion disk, then, like DUH: if it wasn't rotating near c, it would fall straight in and there wouldn't be a disk.

     

    • by Anonymous Coward on Wednesday February 27, 2013 @05:00PM (#43028109)

      By monitoring X-ray emissions from iron ions (iron atoms with some electrons missing) trapped in the black hole's accretion disk, the rapidly-rotating inner edge of the disk of hot material has provided direct information about how fast the black hole is spinning.

      So the summary indicates that measuring the accretion disk somehow tells them exactly how fast the non-emitting portion is spinning.

      The useful answer is in the link from the above quote:

      Risaliti and his colleagues measured X-rays from the center of NGC 1365 to determine where the inner edge of the accretion disk was located. This Innermost Stable Circular Orbit - the disk's point of no return - depends on the black hole's spin. Since a spinning black hole distorts space, the disk material can get closer to the black hole before being sucked in.

      So they calculated the spin of the black hole by comparing the observed orbit to the calculated orbits possible from the calculated mass based on observable gravitic effect on nearby objects. Yes, there's uncertainty there, but until someone discovers a new detail in astronomy, that's as accurate as we can get.

    • Have they shown that the black hole is rotating near c, or just that the accretion disk is rotating near c at the event horizon? The accretion disk and the black hole are not necessarily spinning in sync. If they mean the accretion disk, then, like DUH: if it wasn't rotating near c, it would fall straight in and there wouldn't be a disk.

      I realize this is /., but did you not even read the first sentence of the summary?

      Astronomers have directly measured the spin of a black hole for the first time

      It's not that someone has discovered or theorized about it. They actually measured it. Which I find to be pretty damn interesting.

  • Could the near light speed rotation of the SMB be equivalent in some way to having extra mass at the core of the galaxy? In other words, does this change how much dark matter there must be?
    • Apologies for self-replying...
      .

      In other words, if a lot of SMB material is moving at close to the speed of light, then this would cause a significant mass increase due to this relativistic effect and so the overall mass of the SMB would be significantly higher...helping to explain the current rotational speed of the stars around the center.

      • In addition to what the AC said below, it's my understanding that the galaxy rotation problem is a matter of mass distribution, rather than just plain missing mass. Adding more mass to the black hole in the center would make all the stars orbit more quickly, but it wouldn't affect the relative rotational speed from one star to another. In a system where most of the mass is clustered in the center, the outer orbits should have a lower rotational velocity - simply changing the amount of mass at the center w
        • by jkflying (2190798)

          How about a bunch of black holes which are distributed around the edge of the galaxy?

        • Lots of ideas here. Why don't you run the numbers? Turns out if you do neither of these get close to explaining galatic rotation or other "dark matter" stuff. The facts are that from what we observe, the best explanation/theory right now is dark matter.
          • ?

            What I was describing was a layman's perspective of dark matter. Or are you saying that dark matter doesn't explain galactic rotation or other "dark matter" stuff? Not snark, I honestly can't tell.

            • by Chris Burke (6130)

              What you said was quite correct.

              I'm not sure what they were saying. I think maybe they meant to reply to justthinkit who was actually proposing an alternative?

      • then this would cause a significant mass increase due to this relativistic effect.

        Sorry no. Relativistic mass increase is not the same as rest mass. So no, when get a particle close enough to the speed of light and it stops accelerating. Its local gravity is determined by its rest mass not its relativistic mass.

        • by Chris Burke (6130) on Wednesday February 27, 2013 @08:47PM (#43029873) Homepage

          Its local gravity is determined by its rest mass not its relativistic mass.

          No. Gravity is determined by the stress-energy tensor, and the energy component is total energy, aka relativistic mass (literally, they're the same thing). Relativistic mass is the gravitational mass is also the inertial mass.

          A proton's mass -- the ratio between its acceleration and the force exerted by an electric field -- is much higher than the intrinsic mass of the quarks that make it up. It's the kinetic energy of those quarks held together by the Strong Nuclear Force that gives a proton 90% of its mass. The Higgs Field only explains that last 10%.

          Similarly the gravity of the sun is far greater than just the intrinsic mass of the quarks and electrons inside it. It's the sum of all energy in the sun.

          If you an accelerate an object it gains energy, and therefore (E=mc^2) relativistic mass, and also therefore increased gravity.

          Oh, and yes, this means photons have gravity. Not are affected by gravity (though of course they are) but exert it.

    • by Anonymous Coward on Wednesday February 27, 2013 @05:13PM (#43028237)

      No. Black holes are not dark matter. Well, I mean, yeah, they are dark. Like black dark. Like "how much more dark could they be? None, none more dark." But they are normal matter, not dark matter. The mass of (nearby) galactic core black holes is easily measured by measuring the speed of closely orbiting stars. Their velocity is entirely dependent on the mass inside their orbit, so no need to invoke dark matter.

  • by 140Mandak262Jamuna (970587) on Wednesday February 27, 2013 @04:55PM (#43028065) Journal
    In my limited understanding of these things, (mostly from articles meant for mass consumption, not scholarly journal papers), I imagine a black hole to be so massive not even light can escape its gravitational pull. Which technically means the escape velocity is the speed of light. So anything at the event horizon should be at the speed of light. This is of course, a naive view. The escape velocity is based on Newtonian, not Relativistic, physics.
    • Only if that thing is orbiting at the event horizon, what is another way to say that nothing can orbite there. If the object is just falling, it can be slower.

    • by ceoyoyo (59147)

      No, what you said is insightful. IIRC, anything freely falling into a black hole from infinity would arrive at the event horizon travelling at the speed of light. You're also perfectly free to calculate an escape velocity based on relativity. But this measurement is an (indirect) measurement of the rotation (or at least the angular momentum) of the black hole, not the accretion disk.

      • by meglon (1001833)
        Yeh, the article seems to imply it's a direct measurement, when it's not. And i agree, the OP made a very insightful comment on what can be a really tough thing for a lot of people to grasp.... and me without mod points /sigh.
    • by rocket rancher (447670) <themovingfinger@gmail.com> on Wednesday February 27, 2013 @09:04PM (#43030035)

      In my limited understanding of these things, (mostly from articles meant for mass consumption, not scholarly journal papers), I imagine a black hole to be so massive not even light can escape its gravitational pull. Which technically means the escape velocity is the speed of light. So anything at the event horizon should be at the speed of light. This is of course, a naive view. The escape velocity is based on Newtonian, not Relativistic, physics.

      In Einstein's theory of general relativity, the Newtonian concept of mass doesn't really exist, being spread out over the Einstein curvature tensor on one side of the general relativity equation and the stress energy tensor on the other. Calculating the radius of a gravitational field where the escape velocity is equal to c is straight forward in both Newtonian mechanics and general relativity, and produce the same value, the so called event horizon (Scharzschild radius, technically) but something interesting happens when the gravitational field is generated by a rotating object -- it drags spacetime around with it. [wikipedia.org] This would cause the orbital plane of an object to precess, something that Newtonian mechanics completely misses but was predicted nearly a century ago when people first started exploring solutions to Einstein's equations. Being able to directly arrive at the rotational rates of a wide variety of blackholes (which is what this announcement is all about) means that both frame-dragging and the no-hair conjecture concerning the characterizability of blackholes with just three Newtonian values -- mass, charge, and angular momentum -- can in principle now be studied more rigorously.

  • Not a physicist of any kind, but I had thought that information could not cross the event horizon? If that is true, then how can we construe that the speed of matter near the event horizon indicate the speed of rotation of the black hole? Wouldn't it only indicate the speed of that particular matter? Educate me if I'm wrong!
    • by ceoyoyo (59147)

      You can measure a few properties of black holes. Their mass, charge and angular momentum. All three of these can be observed by the effects they have on nearby matter. The article isn't precisely clear, but I think they're measuring angular momentum by looking at the effect frame dragging has on absorption spectra in the accretion disk.

    • A spinning black hole is distinct because the way space time is draged with the spinning. Basically the only 2 properties left with a black hole is mass and spin.
  • TFA mentions a fact that I'd read about before, that the black hole's rate of rotation increases as it collapses due to the conservation of momentum. But since no matter can actually mover faster than the speed of light, is the collapse limited by this maximum rotation rate? Would the black hole cease collapsing when the rotation rate neared the speed of light?
    • Matter speeds up as the black hole collapses because it moves toward the center of gravity, trading potential energy for kinetic. There's no (practical) limit to the amount of kinetic energy a piece of mass can have, if I have a baseball moving at 99.99999999% the speed of light, I can continue to accelerate that baseball to my heart's content. Though it's acceleration will appear, to an outside observer, to slow down, a baseball's energy will continue to climb at the same rate. The same is true for the

  • If I were to build a disc with its inner ring located near (but not inside) the event horizon of this black hole, and an outer ring located a few million kilometers away, at what speed would the outer section of the disc spin? What would happen along that outer edge?

    • Re: (Score:3, Informative)

      by bughunter (10093)

      It would be ripped to shreds by tidal and frame dragging forces, heated to millions of degrees by frictional heating, emit some very lively photons, and the resulting plasma would become part of the accretion disc.

      And this is assuming you could even get it in place without the same result befalling the construction crew, their equipment, and raw materials.

      • by bughunter (10093)

        Oh, and also, you'd never live to see the completion of the object because time dilation caused by the mass of the singularity would cause all motion near the event horizon to slow to a virtual stop, as seen by an observer at a reasonably safe distance.

        Of course, you can always go visit it yourself to check on the progress... we won't wait for you, though.

        • by PhxBlue (562201)

          Oh, and also, you'd never live to see the completion of the object because time dilation caused by the mass of the singularity would cause all motion near the event horizon to slow to a virtual stop, as seen by an observer at a reasonably safe distance.

          So, kind of like a government contract, then?

          • by meglon (1001833)
            Like a government contract given to a private company, yep.
            • The only thing slower than a contract given to a private company is a task order given to another government agency.

              "What, you mean you guys gave me money to do something, and the closest intersection point between our two offices is at the Cabinet level? Yeah, I'll get right on that."

              • by meglon (1001833)
                Government bureaucracy is cliche, but at least it's usually not near as expensive as doing all the same things, for the same costs, minus the profit and fraud that private companies bring to the mix.
    • by bryonak (836632)

      If I were to take a very long, very rigid (say: diamond) stick with me on one end and someone else sitting on the moon on the other end, then by pushing the stick a bit back and forth we could communicate via the Morse alphabet (ignoring orbital movement, wind drag, etc. for a moment). You'd obviously need something even more rigid (and stronger) than diamond, but keep in mind that light takes some 1.3 seconds for that distance, so this is the maximum speed information can be transmitted with.

      This means tha

  • Are they sure they're not seeing the light-speed reflections of another source? If I shine a laser at the moon and wiggle it, I can make the dot "move" really fast.
  • If the matter on the outer edge of the disc is spinning near the speed of light, and if that matter is gravitationally bound to the rest of the disc and the black hole itself, then eventually the outer edge of the disc should act as a brake on the entire black hole's spin rate (because it can't exceed c). If it were to experience additional imparted momentum, what would happen to spacetime at the edge? I'm curious what the frame-dragging implications of this are.

    Is this simply a matter of the amount of ene

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