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There's a Hole in the Middle of It All

Posted by michael on from the bang-caused-the-hole-in-the-middle-of-it-all dept.

Apparition writes "CNN is reporting that the star at the center of our galaxy is actually a super-massive black hole. The article then claims that it occupies a volume of space about 3 times that of our solar system. If my math is correct, about 230 million suns could fit into that same volume, so it doesn't impress me that the claimed mass of the black hole is only between 2.6 and 3.7 million times that of the sun. So what is up here? Since when do black holes occupy so much space (I thought they were points)? And how can something with a density only 1/100 of our Sun be called super-massive?" I think the article is talking about a maximum possible size of the object, due to limitations on the resolution of our instruments. Nature has a no-registration story about the research. Update: 10/16 23:44 GMT by M : There's an article with more information on space.com, and a press release from the European Southern Observatory.

27 of 572 comments (clear)

  1. I'm no astrophysicist... by AyeRoxor! · · Score: 1, Interesting

    "CNN is reporting that the star at the center of our galaxy is actually a super-massive black hole."

    I'm no astrophysicist, but really, wtf could hold an entire GALAXY together but a black hole? Seriously, any ideas? I may be naive, but I've always thought this to be a stupid ponderance. Sure, anyone with a scientific mind would want proof of its existence, but to be surprised? *Sighhh*

    1. Re:I'm no astrophysicist... by (void*) · · Score: 3, Interesting
      Actually, no, there isn't really enough mass inferred from the luminuous material to keep the galaxies spinning as fast as they do without breaking apart. And no, even the black hole cannot account for all that missing. This problem is known as the dark matter problem in astrophysics.

  2. Down the Drain by (eternal_software) · · Score: 2, Interesting

    I've always thought it was obvious that super-massive blackholes lie at the center of galaxies. The intense gravity at the center should create one, and spiral galaxies are all just pinwheeling "down the drain".

    I would bet there are black holes at the center of ALL spiral galaxies like our Milky Way. Other shaped galaxies may just be at earlier stages of evolution (such as elliptical) before their holes have formed.

    1. Re:Down the Drain by rknop · · Score: 5, Interesting

      I've always thought it was obvious that super-massive blackholes lie at the center of galaxies. The intense gravity at the center should create one, and spiral galaxies are all just pinwheeling "down the drain".

      Several things wrong in here. First, it's the huge density at the center of the galaxy that would lead you to think a black hole might form there. Yeah, the density is big there because it's way down in a gravitational potential well. But intense gravity doesn't create a black hole-- quite the other way around, in fact.

      Second, spiral galaxies are *not* spiralling down the drain. Most of the stars in a spiral galaxy orbit the center approximately circularly; they aren't spiraling in any more than the earth is spiraling into the Sun. So why the spiral shape? Spiral shape can come from a couple of differnet things. In some galaxies, they are density waves. Think of them as a cosmic "traffic jam". In some places, the stars are closer together than other places; in those places, densities are higher, and gas clouds get compressed, and more stars form (which is why spiral arms are bluer). As the wave passes through those stars, they will spread back out. It's similar to sound waves (which are density waves), or, indeed, clumps of cars on freeways (which seem to maintain their identity even though they don't always have the same cars in them-- you pass through them, so for a while you're a part of the clump, but eventually you get past the clump).

      Other theories of spiral structure formation are based on the differential rotation; when a big group of stars form, the differential rotation will tend to stretch it out into a little spiral arm segment. These theories are probably more responsible for spiral structure in galaxies where the arms are ratty and choppy. The density wave theory is probably more responsible in "grand design" spirals where you can trace one long arm all the way from the center out to the edge.

      One thing spiral galaxies are definitely not however are stars spinning down the drain the way water spins down a drain. It may look obvious, but it's wrong. (Yes, there are ways to get material to sink down to the center of galaxies, but generally it's a whole lot easier with gas and dust than with stars. Gas and dust are viscous fluids, but stars are basically collisionless.)

      -Rob

  3. academic implications? by smd4985 · · Score: 3, Interesting

    the scientists in the article seem to assert that this is CONCLUSIVE proof of a black hole's existence. but i remember reading a few months ago about a schism in the physics community - a sizable segment of the community is disputing the theoretical existence of black holes! i wonder how this discovery will affect that debate....

    --
    smd4985
  4. Re:Event Horizon by benwb · · Score: 5, Interesting

    Current theories in no way preclude the formation of a singularity. In fact it is pretty much the required outcome when a sufficiently massive start reaches the end of it's life. There is some discussion that when quantum theory and gravity are unified quantum effects may smear the singularity out of existence, but at this point it is all hand waving. Perhaps what you're thinking of is a naked singularity. A naked singularity is a singularity that is not cloaked by an event horizon, and is extraordinarily unlikely to occur.

  5. Big Black Holes are Thin by afreniere · · Score: 2, Interesting
    I think it was mentioned in "A Brief History of Time" by Stephen Hawking that black holes are actually less "dense" the larger they get. "Density" doesn't actually make a lot of sense here because there isn't really a material to have density, but if you take the mass and divide it by the volume denoted by the Schwarzchild Radius, you get decreasing density with increasing mass. Many have surmised, from this, that maybe the Universe is really a super-mega-humongo-unimaginably-massive black hole whose Schwarzchild radius is a few hundred billion light-years. We're not a singularity because, since we're *inside* the black hole, our time is dilated relative to the outside, and we haven't collapsed yet...

    p.s. I may be wrong about which book mentioned it, but it was one of those uber-cool sci-fact books by a reputable physicist, like Feynman or something. Really. I'm serious.

    -Ansel.

    --
    G=C800:5
  6. Re:They're talking about... by JebusIsLord · · Score: 2, Interesting

    the only problem is, for the brief instant it was within the event horizon almost all of eternity would pass outside it, so we would most likely get the results a bit late :(

    --
    Jeremy
  7. Naked singularities by Jon+Erikson · · Score: 5, Interesting
    It depends on the angular momentum of the black hole (one of the three properties a black hole can have - size, charge and angular momentum). If it is spinning fast enough (and admittedly this is faster than is likely through natural causes) then the event horizon becomes flattened, and at fast enough speeds it becomes flat enough that a naked singularity may become visible.

    Of course this is all based upon classical arguments, and without a theory of quantum gravity we can't be sure. However it hasn't stopped Hawking and Penrose arguing about "cosmic censorship principles" :)

    --

    Jon Erikson, IT guru

  8. Light bends in gravity. by Bonker · · Score: 5, Interesting

    Theoretcially (we'll likely never have building materials struturally sound enough to test this) light should behave in almost exactly this manner close to a black hole. For example, say you've built a circular torus space station around a black hole. If you're within a certain radius to the singularity, but still outside the event horizon, light will bend towards the blackhole, allowing your vision to see 360 degrees around the torus. You can stand in one point and see your back an apparent distance equal to the circumfurence of your imaginary torus away. Closer than that radius means that the torus would appear to bend the wrong way.

    --
    The next Slashdot story will be ready soon, but subscribers can beat the rush and slashdot the links early!
    1. Re:Light bends in gravity. by Bonker · · Score: 2, Interesting

      I love the example they use. They talk about sliding a coffin into a grave at a fraction of the speed of light sufficient to length-contract the coffin by 1/5 (or the grave, to the POV of the pall bearers...)

      Ultra Undertakers deliver a coffin to the graveyard by sliding it along the ground at such a high velocity that the Lorentz contraction factor is gamma = 5. The gravediggers have dug a hole for the coffin with the same proper length as the proper length of the coffin itself. Thus a snug fit is possible when the coffin is at rest. In the frame of the gravediggers, the coffin is Lorentz contracted by 1/5 and so the coffin readily falls in. However, in the frame of the undertakers, it is the grave which is length contracted and so the coffin will surely not fall in.

      The idea is, of course, that the coffin is not rigid and would have to flow into the grave, the front coming to rest before the end:

      As so often happens, the resolution of this paradox rests with simultaneity. If we say that the coffin begins to fall in the gravedigger's frame at t=0 (i.e. the instant the rear of the coffin passes over the edge of the grave) then in the undertaker's frame, the rear will also start to fall at t'=0 but the front will start to fall at an earlier time. In fact the coffin must flow into the hole!

      What amazes me is that the person who came up with this example never stopped to consider what would happen to a planet if you slugged a coffin-sized missile into it at better than 2/3rds c.

      --
      The next Slashdot story will be ready soon, but subscribers can beat the rush and slashdot the links early!
  9. Re:Super-Massive Black Holes by Jon+Erikson · · Score: 4, Interesting
    Yes, because gravitational effects are proportional to M/r^2 and so drop off over distance and increase with mass... but because the radius term is squared it plays a more important role in the strength of the effect.

    As such with a larger black hole (large M, smaller 1/r^2) the difference in gravitational effects over the size of say a person is fairly small because r^2 doesn't change an awful lot. However with a small hole (small M, large 1/r^2) the difference in strength of the gravitational field over the size of a person is a lot larger and so there are tidal forces which tend to cause things to be ripped apart.

    --

    Jon Erikson, IT guru

  10. Re:Event Horizon by Mt._Honkey · · Score: 5, Interesting
    It was a singularity that became the big bang and if the "big crunch" theory is correct, it will probably be a singularity that the universe ends as...
    This is evidently a common misconception among many people. I was just told the currently accepted theory a couple of weeks ago by a physicist at U of I.

    We haven't the foggiest idea what the universe was all the way back to time=0, but starting at at least time = 10^-43 seconds, the universe was a very large, quite possibly infinite, distribution of matter. It was not an explosion away from a point, but an expansion of matter "away". Space time expanded like a rubber sheet, with every point moving away from every other point.

    Neat, eh?
    --

    Don't Bogart the fish sticks
  11. CNN could be wrong by Anonymous Coward · · Score: 2, Interesting

    I don't want to shock anyone, but it is possible that they got the facts wrong. A small black hole (about 2.5 solar masses) has a horizon of a few kilometers (order of magnitude 10km). I am guessing the hole is a few times the size of the SUN not the solar system. That is really huge for a black hole.

  12. How so? by Jon+Erikson · · Score: 5, Interesting
    The general theory of relativity predicts the formation of singularities, but when taken into consideration along with quantum theory as both Stephen Hawking and Roger Penrose have, they become astronomically unlikely(but not impossible). The formation of a black hole would require a mass at least as large as the one in the centre of our galaxy to form a true point singularity and it would have to compress in a mathematically exact symmetrical fashion.

    Eh? Could you explain what you're talking about here? Because as far as I know, Hawking and Penrose's work has nothing to do with the likelihood of black holes forming. Indeed, one of the things about black hole formation in that no matter how unsymmetrical the initial state the end result is highly symmetrical, possessing no distinguishing features other than mass, charge and angular momentum... the "black holes have no hair" theorem.

    Or are you talking about the recent results in M-theory proving Berkentstein's semi-classical formula for black hole entropy? If so, I'm still not sure what that's got to do with black hole formation... it strikes me you've got things confused...

    --

    Jon Erikson, IT guru

  13. Re:Diameter of a Black Hole by Anonymous Coward · · Score: 1, Interesting
    This would seem to imply that, in theory, a very large black hole could have rather low density inside the event horizon.


    No, all black holes with a neutral charge and no spin have the same average density within their swarzchild radius. Big or small, the average density is the same. Any change in mass will change the swarzchild radius of the black hole. Nobody knows what the actual distribution of mass within the black hole is, but most of the math and what little observational evidence has been attributed to black holes, indicate that all the mass is at the center (ie. the singularity.) of the black hole. It's possible, and perhaps fun, to theorize about variations on the theme, but the currently accepted math leads to a constant density.
  14. Story is misleading . . . by Anonymous Coward · · Score: 1, Interesting

    The orbiting star is at 17 light hours. This does not mean the event horizon is at 17 light minutes, but . . .
    The speed of the orbit and the radius gives us the mass of the central object. At 3 million times the mass of the sun it should be VERY bright. Since it is not, and given the very large mass, it can be assumed to be a black hole.
    The Swartzchild calculation does indeed give a event horizon radius of about 8.89E+09 meters, or 29.6 light-seconds, certainly not at the orbit of the detected star.
    By the way, if you do the Swartzchild calculation using the estimates of the mass of the universe you get a event horizon about the size of the visible universe. We may be living in a black hole.

  15. Re:To clarify... by exp(pi*sqrt(163)) · · Score: 2, Interesting
    our understanding of physics breaks down at the edge
    No it doesn't. At least not according to classical General Relativity which describes nice continuous and well behaved properties as you cross over the event horizon. If you approach the mathematics naively it looks like things go to infinity at the horizon but that's due to the cooridnate system being used. Just like the way longitude goes a little awry at the North and South Poles. But this doesn't signify any real problems. Just change coordinates (to Kruskal-Szekeres coordinates for instance) and you have well defined finite fields again.

    Now the singularity is a different matter. No coordinate change can fix things up there.

    --
    Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
  16. Re:Diameter of a Black Hole by renard · · Score: 5, Interesting
    No, all black holes with a neutral charge and no spin have the same average density within their swarzchild radius.

    Are you posting this AC because you know it's false?

    Schwartzschild radius scales as mass; density scales as mass divided by radius cubed; hence the density of black holes scales as 1/mass^2, i.e., as the inverse square of the mass.

    Supermassive black holes are indeed quite un-dense. Taking the extreme limit of this relation, in fact, one finds that the observable universe is approximately the size of its own Schwartzschild radius, i.e., perhaps we are all living inside a giant black hole.

    Damn! There I go again - it makes my head hurt every time I say that.

    -renard

  17. Re:Event Horizon by benwb · · Score: 3, Interesting

    I'm assuming the modern theories that your referring to are the string theories and more recent m-theory. These look promising, and would result in the behavior that you describe. Their predictions about how the formation of singularities are affected by quantum gravity is the discussion that I'm referring to. But unfortunately they have not been able to make a single prediction that can be tested as of yet.
    General Relativity on the other hand, has been extensively verified, and has been correct in every test we've set for it. General Relativity predicts that singularities will form from a collapsing star.
    I still think that m-theory is handwaving until some testable predictions come out of it. BTW, I think that m-theory or one of it's derivatives will provide us a better description of the universe, but not today.

  18. Re:To clarify... by zmooc · · Score: 4, Interesting
    once you cross this, there's no coming back

    Is this true? Could you/someone explain to me what would prevent me from building a huge strong ring around the event horizon and lowering a probe from that ring through the event horizon? The ring could be stabilized by the gravity of the black hole itself and a counter-weight on the side oppossite to the probe. Would the force on the probe be so strong that no force is strong enough to pull it back? Or is it theoretically impossible to build a probe strong enough to withstand the gravity?

    --
    0x or or snor perron?!
  19. Re:Event Horizon by Zack · · Score: 2, Interesting

    Perhaps I meant conservation of angular momentum and not just momentum? Like I said, It's been a while since i've been in school.

    Think of it like a figure skater spinning with outstreached arms. Then pull that arms in and what happens? They spin faster.

  20. Re:Event Horizon by tgibbs · · Score: 5, Interesting
    True, but current theories also haven't proven that inside a black hole _is_ a singularity

    Since we have no unified theory, it is not possible to prove anything mathematically with confidence. The current theory of gravitation, Einstein's general relativity, requires a singularity. But GR is presumed not to be valid at quantum scales of distance, and since a singularity is infinitely small in GR, all bets are off.

  21. Oops. Got one part backwards. by Tackhead · · Score: 3, Interesting
    Argh, I fscked up! (Like I said, relativity's weird ;)

    > From the point of view of you (on the train), looking forward, you'll see the entire universe running about 10000 times normal speed - stars evolving in minutes - and the bullet flying away from you at 2% of the speed of light.

    Argh. The sped-up universe is what a guy on the back of the train looking backwards (and the guy on the black hole probe looking up) sees.

    The guy on the front of the train (and you, lowering the probe and observing the probe) sees a universe running at 1/10000th speed - a 2.0 GHz Athlon will look like it's running at 0.2 kilohertz and what-not.

  22. Re:The Schwarzschild Radius by DjMd · · Score: 2, Interesting

    Of course if you read The Space.com article
    You learn that "An international team of astronomers photographed the star as it zoomed around the galactic center at speeds ultimately exceeding 11 million mph (5,000 kilometers per second). Early this year, the star flitted precariously close to the black hole, coming within 17 light-hours, or just three times the distance from the Sun to Pluto."

    Where the totally incorrect SIZE=3x our solar system came from

    Damn journalists!

    As they say later "'We are far from being able to image the event horizon,' Shoedel said, adding that the star's closest brush with the black hole equates to a radius about 2,100 times larger than that calculated for the event horizon."

    So maybe we should Read these articles?

    but I had fun playing with astrophysics again...

    --
    DJMD - The fourth man - Planetary
  23. Some calculations... by TheSHAD0W · · Score: 3, Interesting

    A friend and I worked out a few calculations on the black hole...

    Assuming it was 3 million solar masses, the diameter of its Schwartzchild limit (effectively the diameter of the black hole) would be 8.8 million kilometers, or about 6-1/3 times the diameter of our sun.

    If the Earth were in orbit around this black hole at the same distance we are from the sun (assuming it wouldn't be torn to shreds by tidal stresses), a year would be 5 hours long.

  24. Re:Diameter of a Black Hole by rknop · · Score: 3, Interesting

    For some reason, I think I remember reading that as matter crosses the event horizon, it's stripped apart at the subatomic level (I suppose due to extreme gravitational forces) and that matter is shot inwards (towards the singulatity), while anti-matter is shot outwards away from the singulatiry. Please do correct me if I'm wrong, but I can look up wherever I read that if you'd like.

    You're thinking of Hawking Radiation. It has nothing to do with matter falling through a black hole, but rather with virtual particle/antiparticle pairs that are being created and destroyed everywhere in space all the time. Thanks to Hesienberg's Uncertainty Principle, you can violate the conservation of energy if you do it over a very short period of time. All around us, there's a sort of "froth" in the vacuum made of electrons and antielectrons which spontaneously are created and then annihiliated. It all happens so extremely fast that nobody could observe any violation of conservation of energy.

    When this happens right on the event horizon of a black hole, however, you can end up with one particle going into the singularity and the other particle escaping. Now, I don't understand the physics of this process in detail! I should-- I ought to look it up. However, what happens is that if the particle/antiparticle pair is created right at the exact spot, it can happen that rather than annihilating each other, they split and turn into real particles. You can observe the particle coming out, and to keep things balanced, the particle going in then has negative energy. The result is that the black hole loses mass (a very tiny amount, mind you). Over time, therefore, black holes evaporate. (Note that many black holes, esp. those at the center of galaxies, are being fed (and thus growing) much faster than they evaporate due to Hawking radiation.)

    The timescale for evaporation of any appreciably sized black hole (solar mass on up to these supermassive black holes) is gigantic-- longer than the age of the universe. Very small ones, though, evaporate pretty quicky. Thus, if there were tiny black holes left over (say) from the Big Bang, we wouldn't expect to find any of them around today.

    As for matter falling into a black hole: the tidal forces get larger and larger as you get closer to the black hole. Of course, this happens with any mass. Tidal forces due to being too close to the moon cause the Earth to stretch a bit and its water to slosh around. If you fall into a solar mass black hole, however, even before you got to the event horizon, the difference in the gravitational force on your feet and on your head would tear you apart. This will happen with all black holes, and it's an issue whether you're inside or outside the event horizon. Indeed, the event horizon is largely irrelevant to it, except as a limit of inevitability. For very large black holes, the tidal forces aren't so bad at the event horizon that you ought to be able to drop through it. For solar mass black holes, the tidal forces will kill you long before you can get to the event horizon.

    If you remember back in 1993 or 1994 when comet Shoemaker-Levy 9 hit Jupiter, it hit in several chunks over the course of several days. The reason was that the comet had been riped apart on a previous pass by Jupiter-- by exactly these same tidal forces. (Comets aren't really held together all that well, as things go, and Jupiter is pretty massive. Tidal forces from Jupiter and the other moons are also what heats up IO and keeps it volcanically active.) My point: tidal forces aren't some mysterious black hole thing, they're something you get with any mass. The only thing about black holes is that you can tend to get a lot closer to that mass than you can with any other form of the smae mass. (E.g., with the Sun, you'd have to be well inside the Sun before the tidal forces got that strong--- but at that point, most of the Sun's mass would be outside your position on the Sun, and therefore you wouldn't be feeling its gravity.)

    -Rob