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Space

Black Hole's "Point of No Return" Found 130

Posted by samzenpus
from the not-coming-back dept.
dsinc writes "Using a continent-spanning telescope, an international team of astronomers has peered to the edge of a black hole at the center of a distant galaxy. For the first time, they have measured the black hole's 'point of no return' — the closest distance that matter can approach before being irretrievably pulled into the black hole. According to Einstein's theory of general relativity, a black hole's mass and spin determine how close material can orbit before becoming unstable and falling in toward the event horizon. The team was able to measure this innermost stable orbit and found that it's only 5.5 times the size of the black hole's event horizon. This size suggests that the accretion disk is spinning in the same direction as the black hole. The observations were made by linking together radio telescopes in Hawaii, Arizona, and California to create a virtual telescope called the Event Horizon Telescope, or EHT. The EHT is capable of seeing details 2,000 times finer than the Hubble Space Telescope."
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Black Hole's "Point of No Return" Found

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  • Editors (Score:5, Informative)

    by Anonymous Coward on Sunday October 14, 2012 @10:20AM (#41649141)

    What in the name of everything you hold holy were you thinking when posting this?

    Sure, the news is interesting, but while we're getting used to spelling errors and broken links on the front page, a blatantly mis-formatted link is something new, I think.

  • That link cleaned up (Score:5, Informative)

    by madcarrots (308916) on Sunday October 14, 2012 @10:23AM (#41649161)

    If you're too lazy to cut and paste. :)

    http://news.harvard.edu/gazette/story/2012/10/point-of-no-return-found/ [harvard.edu]

  • by Anonymous Coward on Sunday October 14, 2012 @10:37AM (#41649261)

    The Event Horizon concerns massless particles (e.g. light) , the Stable Orbit massive.

  • by madcarrots (308916) on Sunday October 14, 2012 @10:37AM (#41649263)

    as i understand it, the Event Horizon is the singularity limit from which light cannot escape. the Innermost Stable Orbit is the closest distance a physical object in space can orbit the black hole without being sucked into it.

  • Re:Unstable? (Score:4, Informative)

    by mbone (558574) on Sunday October 14, 2012 @11:47AM (#41649685)

    In Newtonian gravity, 2-body orbits are stable, unless there is drag or some other non-gravitational force.

    In General Relativity, orbiting bodies emit gravitational radiation, which carries away orbital energy, and so no orbit is truly stable. However, this only really becomes important near a neutron star or (even more so) near a black hole, where the gravitational radiation energy loss can be significant, and objects can spiral into each other fairly rapidly.

    Of course, in either theory, the question of the stability of 3 or more body orbits is very complicated, and still an open area of research, but suffice it to say that N >2 body orbits need not be stable, although ejection of orbiting material is more likely than capture by the central body.

  • by Anonymous Coward on Sunday October 14, 2012 @11:58AM (#41649761)

    Nonsense. Light can fall into a stable orbit too! And light, because it's moving, has mass too.

    Maybe you meant matter, when talking about the stable orbit.

    Ugh. No. Photons have no mass. They have momentum. Relativistic mass isn't actually mass, and in fact, physicists have been trying to get rid of the term, because of the confusion it causes.

    Point of no return = distance below which no stable orbit can exist. If you have thrust, you can actually get out of the "point of no return", it's further away than the event horizon. You just can't have an unpowered orbit that won't eventually decay into the event horizon.

  • Re:Unstable? (Score:4, Informative)

    by mbone (558574) on Sunday October 14, 2012 @12:05PM (#41649797)

    I regard this as basically a red herring, not to mention mixing up two different things.

    The epicyclic frequency and disk stability has to do with the fluid dynamics of an accretion disk - that kind of stability does not require a black hole (look at Saturn's rings, which also have sharp edges).

    The key word in Innermost Stable Circular Orbit is "stable" - the meaning is not that this orbit is not decaying (it is), but that it is stable to small perturbations. Inside the ISCO, a small perturbation will cause big changes, and the orbit will rapidly decay. So, outside the ISCO, the orbit is slowly decaying - "inspiraling" - while inside the ISCO, the orbit will decay very rapidly (i.e., "plunge" into the black hole). But, still, if you had a super-duper rocket, you could escape to infinity from inside the ISCO, as long as you hadn't crossed the event horizon.

    All of this ignores tidal deformations, which convert orbital energy into heat and can also rapidly decay orbits.

  • inaccurate summary (Score:5, Informative)

    by bcrowell (177657) on Sunday October 14, 2012 @01:48PM (#41650485) Homepage

    The harvard.edu news article, quoted in the slashdot summary is inaccurate. It says:

    For the first time, they have measured the black hole's "point of no return"-- the closest distance that matter can approach before being irretrievably pulled into the black hole.

    This reads as a claim that they've resolved the event horizon. That's not true, although there are good prospects for resolving the event horizon of a black hole in the near future.

    As is made clear in the rest of the article, and in the abstract [sciencemag.org] of the published paper, what they've really resolved is structure inside the innermost stable circular orbit (ISCO) [lsu.edu].

    In units where G=1 and c=1, the radius of the event horizon is 2M, where M is the mass of the black hole. The radius of the ISCO, for a nonrotating black hole, is 6M, i.e., three times the radius of the event horizon. What they've resolved is structure at 5.5M.

    The first author of the paper, Doeleman, seems to post all his papers on arxiv.org, but unfortunately this one doesn't seem to be there yet, and Science has their copy paywalled.

  • by siride (974284) on Sunday October 14, 2012 @09:01PM (#41653401)

    Not everybody in the "third world" lives like that.

  • Re:Editors (Score:5, Informative)

    by L4t3r4lu5 (1216702) on Monday October 15, 2012 @05:37AM (#41655725)
    This isn't the event horizon. This is the closest distance matter can achieve a stable orbit. It's approx 5.5x the event horizon radius, where light cannot escape.

    Of all of the things the editor got wrong on this post, this is one of the things actually stated in the stub. I can forgive you for not getting that far, though; This post is utterly appalling.

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