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posted by janrinok on Sunday June 01 2014, @02:59PM   Printer-friendly
from the it-keeps-getting-more-complicated dept.

Zilong Li and Cosimo Bambi with Fudan University in Shanghai have come up with a very novel idea--those black holes that are believed to exist at the center of a lot of galaxies, may instead by wormholes. They've written a paper [abstract], uploaded to the preprint server arXiv, describing their idea and how what they've imagined could be proved right (or wrong) by a new instrument soon to be added to an observatory in Chile.

From the article:

Back in 1974, space scientists discovered Sagittarius A* (SgrA*) - bright source of radio waves emanating from what appeared to be near the center of the Milky Way galaxy. Subsequent study of the object led scientists to believe that it was (and is) a black hole - the behavior of stars nearby, for example, suggested it was something massive and extremely dense.

What we're able to see when we look at SgrA* are plasma gasses near the event horizon, not the object itself as light cannot escape. That should be true for wormholes too, of course, which have also been theorized to exist by the Theory of General Relativity. Einstein even noted the possibility of their existence. Unfortunately, no one has ever come close to proving the existence of wormholes, which are believed to be channels between different parts of the universe, or even between two universes in multi-universe theories. In their paper, Li and Bambi suggest that there is compelling evidence suggesting that many of the objects we believe to be black holes at the center of galaxies, may in fact be wormholes.

Plasma gases orbiting a black hole versus a wormhole should look different to us, the pair suggest, because wormholes should be a lot smaller. Plus, the presence of wormholes would help explain how it is that even new galaxies have what are now believed to be black holes - such large black holes would presumably take a long time to become so large, so how can they exist in a new galaxy? They can't Li and Bambi conclude, instead those objects are actually wormholes, which theory suggests could spring up in an instant, and would have, following the Big Bang.

 
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  • (Score: 3, Informative) by maxwell demon on Sunday June 01 2014, @07:35PM

    by maxwell demon (1608) Subscriber Badge on Sunday June 01 2014, @07:35PM (#49972) Journal

    1) The black hole at the centre of the galaxy is assymmetric enough to emit gravitational radiation itself, which is unknown but possible.

    No, I wasn't assuming that. The orbiting stars emit gravitational radiation due to the very fact that they orbit around the center of the galaxy. They do so even if they orbit a completely spherical black hole (or even if what they orbit isn't a black hole at all). Yes, it's extremely little gravitational radiation, but it's not zero.

    2) The rate at which binary systems in the galaxy as a whole emit gravitational radiation is sufficient to cause them to inspiral -- which it very much is not, since the emission of the gravitational waves acts instead to symmetrise the system, meaning that the binary (or tertiary etc.) systems will tend to collapse *on themselves* while their centre of mass continues to orbit as before. This is unlikely to be so since we know of many binary systems that have singularly failed to fall into the centre of the galaxy despite one or even both of their members being M type stars and roughly as old as the galaxy itself.

    The stars (no matter whether solitary stars or binary system, all orbit the center of the galaxy. That's the rotation I'm referring to.

    3) That the rate of friction, both physical with matter in the galaxy, and dynamical with other stars in the galaxy, is significant enough to cause an inspiral within the lifetime of stars in the galaxy. That it isn't is amply demonstrated by the sheer numbers of M type stars which are as old as the galaxy itself.

    This one I explicitly did not assume. Quite the opposite: I explicitly states that it will happen long after the stars burned out, that is the exact opposite of what you claim I assumed. Of course the matter of the stars doesn't magically disappear when stars burn out (some of it will go into local black holes, but for those the same mechanisms apply).

    4) That these effects, if present, will be short on the timescale of the black hole's own lifetime.

    You're right, I indeed did not take Hawking radiation into consideration; that might indeed save the matter from falling into the black hole (note however that the black hole only starts to shrink after the CMB temperature falls below the black hole's Hawking temperature, which for supermassive black holes is extremely low.

    Indeed, it seems much more likely that the rate of inspiral is extremely long in relation to stars' own lifespans and that instead the stars in our galaxy will have burned themselves into tedious carbon/iron/neutron husks many untold billions of years before there would be significant inspiral.
    And not coincidentally, my post you replied to contains the following sentence: "However, this will happen long after the last star has burned out." I think for a short two-sentence post, it's not to much to ask that you read both sentences before you answer.

    These being so, I don't think it's particularly fair to say that everything will inevitably slam into the black hole at the centre of our galaxy, since on a timescale shorter than any of these effects we will also be colliding with Andromeda

    Well, my post you replied to also contained the following: "(assuming there's no other disturbance, like another galaxy colliding with ours)" so I already explicitly accounted for that possibility. But thanks for the information that this will indeed happen.

    tl;dr: The only mistake in my post is that I forgot about the Hawking radiation, which may indeed allow the matter in the galaxy escape the black hole by the black hole evaporating away before the matter reaches it (ignoring the collision with Andromeda, a fact I didn't know about but which is already accounted for in the conditions I gave).

    --
    The Tao of math: The numbers you can count are not the real numbers.
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  • (Score: 1, Interesting) by Anonymous Coward on Sunday June 01 2014, @08:22PM

    by Anonymous Coward on Sunday June 01 2014, @08:22PM (#49983)

    Ouch, I just got served. Full and unreserved apologies.

    • (Score: 2) by maxwell demon on Sunday June 01 2014, @08:43PM

      by maxwell demon (1608) Subscriber Badge on Sunday June 01 2014, @08:43PM (#49985) Journal

      Well, no problem, we all make mistakes. Anyway, after all you did identify a mistake in my post, namely that I forgot the Hawking radiation. Since we are speaking about the competition of processes which are all very slow, it isn't obvious (at least not to me) which one would eventually win (for an undisturbed galaxy).

      BTW, I just now notice that there's another possibility I didn't think of: An accelerating expansion of the universe might rip the galaxy apart before the black hole in the center had time to eat it (assuming it would otherwise live long enough).

      --
      The Tao of math: The numbers you can count are not the real numbers.
      • (Score: 3, Interesting) by yellowantphil on Sunday June 01 2014, @08:56PM

        by yellowantphil (2125) on Sunday June 01 2014, @08:56PM (#49990) Homepage

        which one would eventually win (for an undisturbed galaxy)

        I hear that the Andromeda Galaxy has been eyeing us suspiciously for a while now, and Wikipedia tells me that we only have 3.75 billion years or so until a collision.

        There is probably a reason this can't happen, but what if the Andromeda and Milky Way galaxy centers are the endpoints of a single wormhole? What happens if the wormhole endpoints collide? Does the wormhole just disappear, or maybe does some spacetime get severed, leaving a tiny, doughnut-shaped universe that used to be the wormhole?

        • (Score: 1, Interesting) by Anonymous Coward on Sunday June 01 2014, @10:02PM

          by Anonymous Coward on Sunday June 01 2014, @10:02PM (#50007)

          Both ends would just be a black hole, so a nice big black hole with a highly disturbed galaxy orbiting around it.

          Entertainingly, that's actually supposition -- good luck calculating what happens when black holes collide. We can basically do it, but we're always rather inhibited by concepts such as an "event horizon". The problem is that an event horizon is total, but grows as a black hole takes in mass, which unfortunately means that something which at time x is well outside what looks like the event horizon is in fact well inside the event horizon as seen from x + 100000000 years. This has a... complicating effect on simulations, which are also somewhat hindered by the tendency of your grids to fall into the black hole.

          We also have no idea what would happen if two singularities crashed, not least since we can't model a singularity anyway, by definition. What to my mind would be even more fascinating would be to take one Schwarzschild hole (spherical, non-rotating) and smash a Kerr hole (non-spherical, rotating) into it. This is fascinating because the internals are totally different: a Schwarzschild hole has that famous inevitable singularity lurking greedily in your future; but a *Kerr* hole's singularity is both cylindrical with a nice friendly hole in the middle of it, and doesn't lurk inevitably in your future anyway. On the diagrams (Schwarzschild: http://online.kitp.ucsb.edu/online/colloq/hamilton1/oh/penrose_Schwpar.gif [ucsb.edu] Kerr: http://www.phys.utk.edu/daunt/Astro/Overheads/BH/Penrose%20Rotating%20BH.jpg [utk.edu]) the Schwarzschild singularity is horizontal, and since all motion has to be in lines 45 degrees from vertical and moving upwards, you're fucked. This is a "spacelike" singularity since it cuts across timelike motion. The Kerr singularity, on the other hand, is vertical, and we can easily see that if we're clever we can avoid it, particularly given the hole in its insides. Of course, have fun trying to navigate inside a black hole and rather you than me because not just your sense of direction but your very sense of *dimension* will be fucked up, but even so. The interest would be what happens? The Kerr hole will evidently disrupt the Schwarzschild geometry such that it can't be Schwarzschild anymore, that's straightforward, and the end result will be another Kerr hole, through conservation of angular momentum if nothing else, but how does it get there? What happens to the singularities? How do they restructure themselves? What would happen if we smacked a Schwarzschild hole with *two* counter-rotating Kerr holes? Or, even better, with six of them, keeping all possible isotropy?

          So far as I know, these questions are unanswerable except that we basically know the starting and ending states. It doesn't help that as soon as you fire a Kerr hole at a Schwarzschild you can't use *either* solution and have to model it numerically. (Both Schwarzschild and Kerr are global; they assume there is no other gravitating matter in the universe.)

          Something else along the same lines would be to take a Schwarzschild hole, and then fire an electron into it, dead at the centre. This imaprts a charge. A *charged* spherical black hole is a Reisser-Noerdstrom hole, and internally it looks a lot like Kerr. The singularity isn't cylindrical but it also isn't inevitable. So firing that one electron into the hole has totally rearranged the hole's insides. How about firing it in off-centre? Then the hole picks up a tiny angular momentum along with its tiny charge, and becomes what is known as a Kerr-Newman -- charged and rotating. The insides are basically identical to a Kerr with unimportant differences, but again the fundamental nature of the hole has changed.

          I think the thing to take away from this is that if we're under attack from aliens using a wormhole we should just squirt a few electrons into it and that's their wormhole fucked. Unless they're instead navigating inside a Kerr and coming from that weird patch of space with a naked singularity glowing in the middle (which the diagram above is slightly oddly calling an "antigravity universe" and I'm not totally sure why), in which case we can just chuck rubbish into it against the spin until it balances, and then that's their wormhole dead.

          • (Score: 0) by Anonymous Coward on Monday June 02 2014, @11:58AM

            by Anonymous Coward on Monday June 02 2014, @11:58AM (#50162)

            Something else along the same lines would be to take a Schwarzschild hole, and then fire an electron into it, dead at the centre. This imaprts a charge. A *charged* spherical black hole is a Reisser-Noerdstrom hole, and internally it looks a lot like Kerr. The singularity isn't cylindrical but it also isn't inevitable. So firing that one electron into the hole has totally rearranged the hole's insides. How about firing it in off-centre? Then the hole picks up a tiny angular momentum along with its tiny charge, and becomes what is known as a Kerr-Newman -- charged and rotating. The insides are basically identical to a Kerr with unimportant differences, but again the fundamental nature of the hole has changed.

            Actually, the electron has an intrinsic angular momentum (spin!), therefore even a centrally falling electron will give the black hole an angular momentum. BTW, from a quantum mechanical point of view, you'll change it from a bosonic to a fermionic black hole (assuming those terms make actually sense for black holes).

            Another interesting fact is that the gyromagnetic ratio of a charged black hole is 2, just as for an electron (without QED corrections, but then, the black hole gyromagnetic ratio is calculated without QED corrections ass well). Now if you assume the electron were a black hole, what would be its radius? Well, it turns out the electron violates the restrictions for charged black holes; a Reisser-Noerdstrom solution for those parameters would be a naked singularity.

            Maybe if we want to know what the interior of a black hole really looks like, we have to look no further than to the electron.

            • (Score: 0) by Anonymous Coward on Monday June 02 2014, @08:20PM

              by Anonymous Coward on Monday June 02 2014, @08:20PM (#50391)

              "Actually, the electron has an intrinsic angular momentum (spin!), therefore even a centrally falling electron will give the black hole an angular momentum. BTW, from a quantum mechanical point of view, you'll change it from a bosonic to a fermionic black hole (assuming those terms make actually sense for black holes)."

              Ah, but as I suspect you know we'd need a quantum theory of gravity to know how the spin of an electron would interact with the spin of a black hole - they're related, but distinct, concepts. I've no doubt that in a quantum description of a black hole whatever the quantum analogue of the hole's angular momentum is would interact with the spin angular momentum of the electron, but I'm not feeling up to speculating just how at the minute. (It's possible that people working on loop quantum gravity have an idea. Alas, I don't know all that much about loop quantum. My impression is both that it's still hard to add matter into the theory, and also that the hole solution they have is Schwarzschild only, but I'm years out of date.)

      • (Score: 1, Interesting) by Anonymous Coward on Sunday June 01 2014, @09:45PM

        by Anonymous Coward on Sunday June 01 2014, @09:45PM (#50002)

        I wouldn't overstate Hawking radiation *too* much -- it gets increasingly slow for increasingly large black holes. I think what's more likely to happen is mergers of dead galaxies will feed the hypermassive black holes at a rate far in excess of the infall from those galaxies -- the various frictions genuinely close to negligible and then, eventually, after many, many tens or hundreds of billions of years, those deadened stars will have started to fall in too. But there's other processes at play, too -- stars are always flung out of galaxies, let alone during mergers, and while yes it's true that future timelike infinity will be in a black hole that's a genuine infinity, whereas it's possible that even the likes of protons are unstable and will decay to radiation quite possibly long before encountering a hole. (Then, eventually, all those holes will themselves have decayed back to radiation, which will occasionally collide with enough energy to make matter -- or even tiny holes, and then back to radiation, like little eddies in the superlong wavelength radio waves. If we believe Penrose then since distance becomes quite meaningless in a pure-radiation universe, we could have a phase transition back to the radiation-dominated era at the start of another big bang, but he has never published anything on that one.)

        With acceleration, it really does depend on what's causing that. The acceleration is a feature of a smooth universe, and any local gradients will muck up the pressure, quite possibly enough to stop it from locally being "anti-gravitational" at all. A gradient-dominated field would have an equation of state of w=-1/3 (so satisfying the weak energy condition, barely, rather than violating it), and a velocity-dominated field has a super-stiff equation of state w=-1. The equation of state will therefore be highly position-dependent and range between -1 and 1, and we need between -1 and -1/3 to get an acceleration. It's possible then that an acceleration caused by a quintessence will not tear galaxies apart because it simply won't act that way in the presence of lumpy matter. This effect is naturally heightened if the field couples to matter, such as a Galileon, a chameleon or a symmetron.

        On the other hand, if it's a cosmological constant we still don't have to worry, since even though this will keep an equation of state of -1 everywhere and in every spacetime, we have solutions for things like Schwarzschild-de Sitter (black hole in the presence of a cosmological constant) or Lemaitre-Tolman-Bondi-de Sitter (spherical cluster in the presence of a cosmological constant) and the solutions are stable. The point is that acceleration in this way is a facet of the *global* spacetime, assuming that that spacetime looks like Robertson-Walker and obeys its evolution equations. On a local level, and GR is nothing if not a local theory, it's not necessarily the case.

        (Having fun with phantoms, though, and yeah you'll rip your galaxy apart long before the hole eats it all.)

        Sorry again for being a douche; you're right, somehow in a two-line post I missed an important point in my haste to spew a load of things on page which while broadly accurate were almost irrelevant to your post, which had nothing wrong with it (except perhaps a couple of missed edge cases).