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Space Science

It's Official: Black Holes Have Lots Of Mass 70

Posted by chrisd from the invigorating-galactic-jacuzzi dept.
KewlPC writes "Spaceflight Now reports in this article that some scientists have been able to measure the "weight" (yeah, yeah, it's actually mass, not weight) of a black hole that is (or was, 13 billion years ago) eating up the most distant known quasar, some 13 billion light years away."
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It's Official: Black Holes Have Lots Of Mass More

It's Official: Black Holes Have Lots Of Mass

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  • Duh. (Score:5, Funny)

    by Ayanami Rei ( 621112 ) <rayanami&gmail,com> on Sunday March 23, 2003 @04:15AM (#5577542) Journal
    Even I knew that. I mean, stuff keeps falling in them. You know that last significant figure to which they measured the weight? About 10^-8 percent of that are my keys, for sure.

    • Re:Duh. (Score:1, Offtopic)

      by vladb ( 654075 )
      Being one of the first posts, I have this sudden urge to make a perfect condidate for a -4 karma type of a post.. ehem.. to the matter however.. I'm wondering if any astronomy buffs could help me figure what does it help to know an approximate weight of a black hole? Other than an excuse to aquire more research dollars ;-)

      • Re:Duh. (Score:1, Insightful)

        by Anonymous Coward
        You may have noticed that modern astronomy does not generally have a "goal" other than to get as much information as possible about the universe and assemble theories to explain it. We have not enough technology yet for there to be a true purpose to astronomy. (Unless you count the building of an ISS, ... but the purpose of that is still just to gather data, etc.) This is like screaming, upon seeing Fermat's Last Theorem: "AND WHAT THE HELL ARE YOU GOING TO USE THIS FOR?"

    • Re:Duh. (Score:5, Funny)

      by Alsee ( 515537 ) on Sunday March 23, 2003 @10:40AM (#5578072) Homepage
      About 10^-8 percent of that are my keys, for sure.

      Measurements show that 12% of the mass is single socks. Scientists are still trying to identify the other 88% of mass.

      -
    • I'm interested in how many Libraries of Congress the black whole weighs.

  • Neat (Score:5, Interesting)

    by Anonymous Coward on Sunday March 23, 2003 @04:16AM (#5577547)
    This is neat, I'd never heard of this before:

    The extreme brightness of this quasar also shows that the black hole in its core is swallowing matter at the maximum rate possible. This maximum rate is called the "Eddington Limit". If the black hole were accreting matter any faster, it would shine even brighter, and the intense luminosity would actually exert enough pressure to stop any more material falling in.

    So there's a limit / "max throughput" to how much matter a black hole can suck in? Very interesting.

    • Re:Neat (Score:5, Informative)

      by ndevice ( 304743 ) on Sunday March 23, 2003 @04:34AM (#5577576)
      this is how normal stars work too. The radiation pressure generated by the core keeps the core from collapsing into itself. - well not quite the same, but same idea.

      But I haven't heard of the eddington limit before either. Neat.

    • Re: Neat (Score:3, Funny)

      by Black Parrot ( 19622 )


      > So there's a limit / "max throughput" to how much matter a black hole can suck in? Very interesting.

      Yep, there's bandwidth problems everywhere.

    • Sounds like nature took a que from the internet and enacted something to prevent that /. effect itself.

    • Re:Neat (Score:2)

      by C21 ( 643569 )
      depending on how large it is, yes. There are massive black holes that span entire universes (theoretically) and contain much more than the limit for a small atom sized black hole.
    • I doubt anybody is still reading this thread, but in case you are here is more information.

      The above posts are correct that radiation pressure balances the force of gravity. But luminosity (the amount of radiation) goes up with mass way faster than gravity, so eventually the radiation pressure "wins" and the star gently blows apart. That provides an upper limit to normal stars. When I was taking stellar structure in grad school in the early 90's it was thought the limit is about 60 solar masses. Above
    • the background radiation (4 degress kelvin) is also not uniform... they recently discovered an area of space which was less than 4 degrees kelvin, which remains so because of a "solar" wind (actually cold gas) pushing against the influx of new material/heat.... very interesting.
  • they had to write out the long way how many zeroes a quadrillion had...
  • at least that's what I remember from astronomy classes. The article doesn't say if they take that into account or not - and if it's really so far away, that would be a lot of dust that light travelled through. If they do, they would have to assume some uniform amount of dust?

    • interstellar dust reddens (Score:5, Informative)

      by barakn ( 641218 ) on Sunday March 23, 2003 @05:19AM (#5577643)
      Atoms produce very specific patterns of absorption or emission in the light spectrum depending on species. A familiar example, is the solar spectrum [obspm.fr], which is created by absorption of narrow bands in the spectrum by a large number of different elements in different states of ionization. Redshift causes the entire set of these lines to be moved towards the red end of the spectrum. They retain the spacing between themselves, so they can still be recognized in their new positions, and their new positions tell us how fast the object that created them is moving. Reddening caused by dust doesn't move these absorption lines. Instead it scatters light preferentially at the blue end of the spectrum, causing the entire end of that spectrum to dim, rather than creating narrow bands in it or moving narrow bands around. These two different processes are usually distinguishable.
      • actually, I was thinking more of the fact that they make a relatively big deal out of their redshift measurements as a measure of the distance to the object. Now you have to factor in gravitational redshift + dust + universe expanding + probably some other stuff I can't think of right now.

        • And my point was that the dust is absolutely irrelevant to distance measurements using redshift. Now if we were using the object's magnitude to measure its distance (assuming it's one of those objects with a known absolute magnitude), then dust reddening would matter. QSO luminosities vary so much we'd never use a magnitude technique to guess their distances.
  • Do we know the physical size or the particle density of black holes?

    I'm curious as to whether black holes are compacted so much that most of the space between atoms (and even subatomic particles?) is gone, or whether the repulsions keeping them apart are even stronger than the force of the black hole's gravity.

    Now that they have a measure of the weight, if they know anything about the density or the size, they've got the other value as well.

    • Re:Does this say anything about its size? (Score:5, Informative)

      by ndevice ( 304743 ) on Sunday March 23, 2003 @04:44AM (#5577587)
      You might be confusing neutron stars (pulars sometimes) with these quasars.

      Neutron stars are prevented from collapsing into black holes because of nuclear repulsion / neutron degeneracy (instead of electron repulsion). In fact, there's so much pressure that the electrons get squeezed into the protons of the atoms - hence neutron stars.

      Black holes have enough gravity to overcome nuclear repulsion and collapse further than neutron stars. I think there's a couple theories about just what happens inside the black hole, but the commonality is that particles don't mean much whether or not you're talking about a singularity, or the non-singularity quantum foam theories.
    • The other reply has some good information, but he doesn't cover

      Now that they have a measure of the weight, if they know anything about the density or the size, they've got the other value as well.

      Actually, the Schwarzschild radius of a black hole is proportionate to its mass. A black hole with mass the same as the Sun would have a 3 km radius; so just do the math if you want to find the radius of this one.

      This page [berkeley.edu] has some good info.

      • Re:Does this say anything about its size? (Score:5, Informative)

        by Flamerule ( 467257 ) on Sunday March 23, 2003 @05:09AM (#5577626)
        Gack, I really need to go to sleep.

        I'm right in saying "the Schwarzschild radius of a black hole is proportionate to its mass", but more properly it's directly proportional; i.e., the proportionality constant is 1.

        Well, as long as I'm here, let's do some calculations. The article says the black hole's mass is 3 billion times that of our Sun, so multiply 3 km by 3 billion and you get 3 km * 3*10^9 = 9 billion km. To put things in perspective: the distance to Alpha Centauri is 3.8*10^16 m = 3.8*10^15 km, so this black hole's radius is only .0002% of the distance from here to the nearest star. Quite small, astronomically-speaking.

        • You need it. The nearest star is Proxima Centauri at 4x10^13 km (also, your numbers for Alpha Centauri are erroneous). The 9 billion solar mass black hole's radius is thus .0225% of that distance.

        • Re:Does this say anything about its size? (Score:5, Interesting)

          by Smidge204 ( 605297 ) on Sunday March 23, 2003 @09:54AM (#5577945) Journal
          I'm right in saying "the Schwarzschild radius of a black hole is proportionate to its mass", but more properly it's directly proportional; i.e., the proportionality constant is 1.

          Something about that seems... counterintuitive?

          You're saying that if I have a black hole with a mass of x, it has radius y. Then you say if it has mass 2x, it has radius 2y?

          If a black hole is a sphere, doubling it's radius increases it's volume by a factor or about 33 1/2! Since mass only doubled, it's density just dropped by a factor of 17?

          I admit I'm not very experienced with black holes, but if anything it seems a black hole would condense to some maximum possible density, and it would maintain that maximum possible density regardless of how much mass you add to it... so it just seems strange that doubling it's mass would actually double it's radius.
          =Smidge=

          • Re:Does this say anything about its size? (Score:5, Interesting)

            by taliver ( 174409 ) on Sunday March 23, 2003 @10:49AM (#5578094)
            Actually, a quick googling found this: [aol.com]

            r0=2GM/c^2 (Eqn 10.1.5)

            So it is directly proportional. However, I didn't look closely at the units that they are using here, but thta shouldn't matter to the solution at hand.

            • The units come with the variables in the equation, the Gravitational constant G, and the constant c (the speed of light in a vacuum), and thus it is a complete equation.

              mks units (favored by many physicists):
              G= 6.673x10^-11 N(m/kg)^2

              cgs units (those wacky astronomers!):
              G= 6.673x10^-7 dyne (cm/g)^2

              • However, you can also use systems of equatiosn where c=1 (unitless), leading to many entertaining conversions. There is also one where G=1, which leads to mass in units of meters. That's what I meant by not looking too closely.
          • If a black hole is a sphere, doubling it's radius increases it's volume by a factor or about 33 1/2! Since mass only doubled, it's density just dropped by a factor of 17?

            Correct. In your sphere example, a 2x mass increase will not yeld a 2x radius increase, since the relation between the two is not linear.

            But a black hole is not a physical object, it's an abstraction. The radius of a blackhole is defined as the distance where the escape velocity equals lightspeed. And that distance is directly proportion
            • Ah, that seems to the be point of confusion. If the "radius" of the black hole is the radius of the event horizon instead of the actual core of mass, then at least the 1:1 mass/radius ratio isn't so counterintuitive :)

              Thanks for the clarification.
              =Smidge=
            • But a black hole is not a physical object, it's an abstraction. The radius of a blackhole is defined as the distance where the escape velocity equals lightspeed. And that distance is directly proportional to the black hole mass, hence the 2x radius increase.

              Once a star has collapsed into a black hole, you shouldn't use "radius" to describe it. Because of the way that space is curved inside a black hole, the distance from the central singularity to the event horizon is not a well-defined quantity (and is i
              • While I acknowledge that the geometry radically alters in the presence of intense gravity (in fact, String theory suggests that the number of dimensions collapses inside a black hole to an effective singularity (though protected by minimum plank-radius)), I'm not comfortable using the phrase circumference to describe it's externally apparent dimensionality.

                At the least, you'd have to consider the black hole as a 2D surface (or shell). Which is still related to r^2.

                Only speaking as a well read lay person,
            • The black hole of the story, with billions of solar masses, is probably less dense than water...

              Actually, no. From what I understand, the "size" of the black hole is actually the size of the event horizon, since the black hole itself has a size of zero and infinite density.
          • If a black hole is a sphere, doubling it's radius increases it's volume by a factor or about 33 1/2! Since mass only doubled, it's density just dropped by a factor of 17?

            Actually, radius, circumference, and volume cease to have meaningful correlations in the vicinity of a macro relativistic object such as a black hole.

            Density also is a meaningless measure when it comes to a black hole. Black holes are infinitely dense, since they have a measureable mass but their size is 0. A black hole is a point sour
        • Well, as long as I'm here, let's do some calculations. The article says the black hole's mass is 3 billion times that of our Sun, so multiply 3 km by 3 billion and you get 3 km * 3*10^9 = 9 billion km.

          WTF? Mass varies as the cube of the radius, so the radius must be multiplied by the cube root of 3 billion, which is about 1440. So the size of the black hole is about 4300 km.

          • Mass varies as the cube of the radius

            Err, no. Volume varies as the cube of the radius. Mass at a constant density would as well, but then we're definately not talking about black holes, degenerate matter, or indeed any mass large enough to suffer compression under its own weight.

    • If you're talking about the radius of the event horizon, I believe that is proportional to the black hole's mass.

      If you're talking about the physical size of the matter in the black hole, I don't know if that is something that can be measured. We'd have to find a way of getting data out out from below the event horizon. . .

    • Re:Does this say anything about its size? (Score:5, Informative)

      by Alsee ( 515537 ) on Sunday March 23, 2003 @10:33AM (#5578060) Homepage
      I'm curious as to whether black holes are compacted so much that most of the space between atoms (and even subatomic particles?) is gone, or whether the repulsions keeping them apart are even stronger than the force of the black hole's gravity.

      Ok, first you get netron stars where the space between atoms is gone. The entire star becomes one big "nucleus". Then there are quark stars (I think they may still be uncertain about whether quark stars exist). In a quark star the space between subatomic particles (neutrons protons and electons) is gone.

      THEN you get to black holes. Once you get within a certain distance of a black hole all laws of physics other than gravity effectively cease to exist. It isn't a question of gravity being stronger then the repulsion - the repulsion no longer exists. What happens is that the repulsive force itself gets pulled in by the gravity.

      Think of it this way: Imagine the repulsive force is sound and gravity is wind. A black hole is where the wind is faster than the speed of sound. No matter how strong the repulsive sound is it gets carried inwards. It can't push outwards on anything.

      We don't really understand what happens at this point. All known laws of physics break down within this region. We need to discover new laws of physics. The answer will probably be found in a theory of "Quantum gravity".

      -
      • Minor nit-pick with your analogy.

        The speed of sound in a medium is a function of the average velocity of the molecules in that medium. This is based off of the ideal-gas law, utilizing the probability of direction of particles bouncing off one another.. Collision of gas molecules against solidly compacted forces (such as the front-end of an ship (air/boat), an explosion wave-front, etc) merely causes the molecules to divert their direction, and such ping-ponging causes neighboring molecules to divert, the

    • Re:Does this say anything about its size? (Score:1, Informative)

      by Anonymous Coward
      Do we know the physical size or the particle density of black holes?

      We know both. Err... we know one and we know what general relativity predicts about the other, but we don't know how to merge that with quantum dynamics. The density of the black hole is infinite. Every bit of mass inside it is concentrated into a point of zero size - the singularity. So yes, all of the space between particles is gone. But of course being at such a small size, GR is outweighed by the quantum effects and we don't have a th
      • Now when someone says `black hole' they mean `the event horizon and everything inside it'.

        The use of the word "Inside" is interesting. The event horizon is a physical boundary of the rests of this Universe and what was that formed the black hole. So, outside is just equally appropriate, and equally meaningless (semantically, no offense).

        BTW, text books say the "everything" are only mass and angular momentum. But if this is true, as "all the information of the matter fall onto the black hole will be lo
        • BTW, text books say the "everything" are only mass and angular momentum. But if this is true, as "all the information of the matter fall onto the black hole will be loss save the mass and angular momentum", then the history of the black hole shall went down the sink as well and the claims that stars formed black holes shall become automatically invalidated.

          No? Enlighten me, please.

          If a great battle is fought on a beach, but over time the arrowheads are ground into sand, the shafts rot away, and at some

    • Black holes are compressed matter which is way beyond atoms touching, or even nucleii touching, which would be the famed Netronium. The matter is squooshed down to form a mathematical singularity, where such things as distance become very minquative indeed.
    • Do we know the physical size or the particle density of black holes?

      You pose two excellent questions.

      The physical size of a black hole depends on how you measure it and where you are and what you're doing when you measure it. The gravity near a black hole bends space itself in such a way that rulers contract and clocks run slower. Rulers only contract when in certain directions, and if a ruler is very close to the black hole those directions change randomly, continuously.

      A direct consequence of this
  • Just speculating, but since black holes do evaporate, and the smaller they are the faster they evaporate, I wonder what the implications of evaporation would be in the presense of an acretion disk.

    Given that in the process of evaporation, a black hole emits radiation, at some point the radiation pressure from the evaporation would balance out the force of gravity pulling matter into the black hole so then the black hole might stabilize in size.

    Surely they'll have named that limit already, but I don't thin

    • Re:eddington limit and black hole evaporation (Score:5, Informative)

      by Flamerule ( 467257 ) on Sunday March 23, 2003 @05:24AM (#5577651)
      Given that in the process of evaporation, a black hole emits radiation, at some point the radiation pressure from the evaporation would balance out the force of gravity pulling matter into the black hole so then the black hole might stabilize in size.
      Whoa, whoa. Yeah, a very small black hole would emit enough radiation to completely counterbalance its own gravitational force, so that matter would stop coming flowing into it. But how would that make the size stable? With no more matter coming in, the black hole would just keep emitting radiation, getting smaller, and losing mass, until it evaporates.

      To put it another way, it's not a stable limit, it's an unstable limit. If a black hole is accreting mass at a rate less than or equal to this limit, the black hole will shrink and evaporate; if a black hole is accreting mass at a rate greater than the limit, it will grow.

      • Even worse, the smaller a black hole gets, the more quickly it loses mass, which causes to get smaller even more quickly, which causes it to loose mass even more quickly, etc. Thus, in its final moments, the "evaporation" of a tiny black hole would be at a speed that might be better characterized as "explosion".
    • Only large black holes will have accretion disks. The radiation coming from a black hole is negligible until the black hole itself is tiny. It is my guess that the radiation pressure from a black hole would never be enough to prevent a net gain of mass.
      • Only large black holes will have accretion disks. The radiation coming from a black hole is negligible until the black hole itself is tiny. It is my guess that the radiation pressure from a black hole would never be enough to prevent a net gain of mass.

        Actually, very tiny blackholes can shrink. The radiation from a black hole is blackbody radiation resulting from the hole's "temperature", measured as the amount of chaos the matter that fell into the hole possessed.

        As a hole gets smaller, that amount get
    • It is my understanding that black holes emit a very small amount of radiation, and do it very slowly. Therefore, the black hole would have to be very small (thereby having very little gravity) for this to take place.

      Besides, a black hole would have to swallow all the matter within its reach before it could shrink to the size necessary for the effect you describe to take place, because the more matter it takes in, the bigger it gets. And since it would have already taken in all the matter it can get ahold o
    • The radiation that makes black holes look bright comes from stuff falling in. I don't know what the mechanism is, but the energy comes from the mass's gravitational potential energy. So radiation, and therefore radiation pressure, increases (proportionally?) with how much mass is falling in per unit time. So the eddington limit is a limit on the black hole's accretion rate, not it's size.

      Black hole evaporation is a slow process. It has essentially no effect on big black holes, and it isn't relevant t

  • the "weight" (yeah, yeah, it's actually mass, not weight)

    What was all that about? Why not just say "the mass"? This is on a site that uses computer and physics jargon and acronyms all the time, mass isn't exactly an obscure concept.

    • The headline talks about "weighing" the black hole, so I used the word weight. But I knew I'd get reamed if I didn't mention that it's actually the mass of the black hole, not its weight, so I put that in there too. So much for hedging my bets.

      But you're right. I should've written mass and left it at that.
  • One Quadrillion Earths is impressive and all, but let's stick to standard units [slashdot.org] people!
  • ...but I didn't even know they were Catholic!
  • That is a new low for Slashdot. An article about something which occurred 13 billions years ago?
    What next? The weather forecast for the previous Big Bang?
  • This black hole is 13 billion LY away, and thus became a black hole sometime slightly longer than 13 billion years ago, and was born as a star shortly before that...

    This timeline [pbs.org] gives the birth of stars at occuring roughly 1 billion years after the big bang, which this [space.com] article in January gives at between 11.2 and 20 billion years ago...

    Wouldn't this hole place a lower limit of 14 billion years on the bang? And if last year's Hubble estimate of 13-14 billion years ago for the bang is right, wouldn't it pi

  • MgII (Score:1)

    by gfim ( 452121 )
    The article talks about a MgII line in the spectrum. Surely that's meant to be Mg++.

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