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posted by takyon on Monday August 22 2016, @09:27PM   Printer-friendly
from the no-escape-for-sanic dept.

One of the common descriptions of black holes is that their gravitational pull is so strong, not even light can escape it. Stephen Hawking is famous for (among other things) showing that this isn't actually true. The Hawking radiation that bears his name allows matter to escape from the grip of a black hole. In fact, Hawking's work suggests that an isolated black hole would slowly evaporate away and cease to exist.

But his work remains entirely theoretical. Hawking radiation is expected to be so diffuse that we could only detect it if we could somehow find or create a black hole isolated from all other matter. But Jeff Steinhauer of Israel's Technion has been on a sometimes single-handed quest to develop a system that can accurately model a black hole's behavior. And, in a recent paper in Nature Physics, Dr. Steinhauer describes how his model system generates what appears to be Hawking radiation.

[...] The implications are significant, and Steinhauer puts them succinctly: "The measurement reported here verifies Hawking's calculation, which is viewed as a milestone in the quest for quantum gravity. The observation of Hawking radiation and its entanglement confirms important elements in the discussion of information loss in a real black hole."

Observation of quantum Hawking radiation and its entanglement in an analogue black hole (DOI: 10.1038/nphys3863) (DX)


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  • (Score: 2) by bob_super on Monday August 22 2016, @09:54PM

    by bob_super (1357) on Monday August 22 2016, @09:54PM (#391890)

    > Hawking's work suggests that an isolated black hole would slowly evaporate away and cease to exist.

    Nobody's ever managed to explain to me how the black hole goes from losing mass to not existing, without going through an interesting state where it's not heavy enough to be a black hole.
    I understand the "evaporation", which I'm not sure can happen fast enough to even matter over a universe-age duration, but fine, it's an "isolated" hole thought experiment already. But once you drop back down below the mass at which gravity overpowers light, what's that object?

    • (Score: 2) by takyon on Monday August 22 2016, @10:06PM

      by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Monday August 22 2016, @10:06PM (#391894) Journal

      Doesn't the radius of the black hole shrink rather than the density?

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    • (Score: 0) by Anonymous Coward on Monday August 22 2016, @11:25PM

      by Anonymous Coward on Monday August 22 2016, @11:25PM (#391925)

      Black holes can form today when stars cool and collapse. It's speculated that close to the Big Bang, less massive black holes may have formed. The smaller the black hole, the more Hawking radiation is expected from it. Stellar black holes won't finish evaporating for some time yet, but primordial ones could be vanishing now. There would be a flash as they vanish.

      https://en.wikipedia.org/wiki/Primordial_black_hole [wikipedia.org]

      • (Score: 2) by HiThere on Tuesday August 23 2016, @12:48AM

        by HiThere (866) Subscriber Badge on Tuesday August 23 2016, @12:48AM (#391951) Journal

        But don't you then get a naked singularity? And that's supposed to be something that you really don't want to have wandering around...though I've never really understood why. Somehow they seem to be thought more abhorrent than black holes.

        IIUC, Hawking claimed that the universe didn't start at any particular instant to prevent the existence of a naked singularity at the beginning of time, so he really didn't like the idea, and then he went and invented a way for black holes to evaporate leaving a naked singularity behind. Whoops!

        So can someone tell me what the effect of a naked singularity would be?

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        • (Score: 1) by Kenny Blankenship on Tuesday August 23 2016, @01:27AM

          by Kenny Blankenship (5712) on Tuesday August 23 2016, @01:27AM (#391956)

          In space, no one can hear the sound of one hand clapping.

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    • (Score: 3, Insightful) by PinkyGigglebrain on Monday August 22 2016, @11:31PM

      by PinkyGigglebrain (4458) on Monday August 22 2016, @11:31PM (#391927)

      Uh, once a black hole no longer has the mass to be a black hole it "ceases to exist" as a black hole. What ever mass is left would probably just become a Neutron star according to current physics. Once the left over matter is clear of the time stopping effects of being inside an event horizon the protons/electrons/neutrons will continue to decay and eventually cease to exist all together becoming just a bunch of free Quarks.

      Of course all this assumes Humanities current understanding of the Universe is (mostly) correct.

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    • (Score: 5, Informative) by deimtee on Tuesday August 23 2016, @12:20AM

      by deimtee (3272) on Tuesday August 23 2016, @12:20AM (#391943) Journal

      Using relativity, there is no minimum mass to a black hole, its radius is just smaller for lower mass (and can never shrink).
      Adding quantum effects, a la Hawking, allows mass to leak from a black hole*. This leakage is inversely related to the size of the hole. Stellar size black holes would leak very slowly, but by the time you get down to interesting sizes the radiation is a runaway effect that is basically a massive explosion, and the hole 'evaporates'.

      * [simplified] virtual particle pair production near the event horizon can result in one particle falling into the hole and one escaping. Since the energy to separate the particles came from the black hole twisting space this actually costs the hole mass.

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