It's Official: Black Holes Have Lots Of Mass

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."

Comments

Duh.

[Ayanami Rei]

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.

[Alsee]

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.

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Re:Duh.

[robson]

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

Scientists have informally labeled the remaining 88% dark socks. ;)

Neat

[Anonymous Coward]

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

[ndevice]

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

[Black Parrot]

> 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.

not giving people much credit

[ndevice]

they had to write out the long way how many zeroes a quadrillion had...

interstellar dust does red shifting too

[ndevice]

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?

Does this say anything about its size?

[mcgroarty]

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?

[ndevice]

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.

Re:Does this say anything about its size?

[Flamerule]

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 has some good info.

Re:Does this say anything about its size?

[Flamerule]

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.

Re:Does this say anything about its size?

[Smidge204]

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?

[Alsee]

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".

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Re:Does this say anything about its size?

[taliver]

Actually, a quick googling found this:

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.

Re:Does this say anything about its size?

[at_18]

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 proportional to the black hole mass, hence the 2x radius increase.

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

That's probably true, since in theory a black hole is empty, except a point in its center where all the mass is concentrated at inifite density - so if you double the mass, you get double infinite density, which is still infinite :-)

Average density continues to drop as you add more mass. The black hole of the story, with billions of solar masses, is probably less dense than water...

Re:Does this say anything about its size?

[maraist]

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, I've heard black holes being described as 2D planes; all the mass exists within the event-horizon (since time slows down as you approach it, approaching the speed of light).

That being said I can almost comprehend space being warped enough such that the r^2 flatens out to r, but It's still beyond me.

Re:Does this say anything about its size?

[maraist]

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, thereby causing an effective motion of the gas. When a large body of such molecules move in the same direction (on average), we call this a current.

Wind is such a current, rivers are such a current, electrons propagating along a conductor is such a current. In each of these cases, a single particle (molecule/electron) is not moving the entire length, but the net motion of all the colliding and direction-changing particles is.

Thus, as with the speed of light, for net-aggregate-velocities (current velocity) much much lower than the average velocity of a given particle in the medium, you can use linear superposition. Namely, if you are in a car moving at velocity x, and you through a book forward at velocity y, then until air-resistance slows you down, the book will have velocity x + y.

However, as you approach the average speed of a particle in your medium, the particles on your wave-front can't move forward fast enough to "get out of your way", so the apparent friction becomes non-linear (polynomial, in fact). You are now accelerating the particles in front of you, and apparently gaining mass (as far as propulsion is concerned). BUT, the key is that you are accelerating the particles in front of you.

I believe the formula for friction in an ideal gas is something similar to:
1 - V^2/Vavg^2

Which is related to the lorenz contraction factor.

Ideal gas law does not mean that no particle ever travels faster than the average.. In fact, if enough energy is released into the gas such that it's temperature (e.g. aggregate kinetic energy) rises, the it's average velocity is indeed increased.

Thus my nitpick is that for the analogy where a repulsive force is sound and gravity is wind.. As your "wind" velocity increases, you are, in fact, increasing the average velocity of particles. Any perterbations (shock waves, aka sound), now can propagate faster, though in a non uniform manner (the direction of the wave will be faster in the direction of the wind (parallel direction), average in orthogonal directions and dramatically attenuated in anti-parallel directions).

Further, if the auditory devices (sound-generator, and target) are carried along with the medium, then their relative velocities will be constant with respect to the medium, and sound will effectively probagate uniformly.

There is one tiny wrinkle in all this. Here, the max velocity is consdered to be Vavg and is changable. In quantum physics, Vavg is the speed of light and can never be exceeded (at least on average). Thus linear superposition breaks down. Increasing the velocity of the wind means that particles ricocheting forward can't produce a net propagation velocity twice as fast relative to a stationary transmitter/reciever.

Theoretically, all the quantum "forces" are effectively energy moving through space and time at different ratios. Plotting them together as a 4D space-time plot, the magnitude of the 4D coordinate should always equal c. Thus if you are traveling along the event horizon at c in any one direction, then you should have no remaining ability to travel in any other directions (including time). Thus perterbing the medium should be impossible. The event horizon would be like having a steel shell that is oblivious to outside disturbances (ignoring that steel allows for elastic collisions, including sound). I speculate (as a lay person) that the reasoning that event horizon particles are oblivious to anti-parallel disturbances is because they have

eddington limit and black hole evaporation

[ndevice]

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 think it's the same as the eddington limit.

Or perhaps there won't be a limit here because the cross section area of the acretion disk would be so small compared to the surface area of the event horizon. (yes, I think that incoming matter would have to form a disk and not form an acretion shell)

Re:eddington limit and black hole evaporation

[Flamerule]

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.

Re:eddington limit and black hole evaporation

[barakn]

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.

Re:eddington limit and black hole evaporation

[KewlPC]

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 of, the effect you mention wouldn't happen.

interstellar dust reddens

[barakn]

Atoms produce very specific patterns of absorption or emission in the light spectrum depending on species. A familiar example, is the solar spectrum, 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.

Re:interstellar dust reddens

[barakn]

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.

Someone's bitter memories of high-school physics?

[tunah]

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.

I hope you got some sleep...

[barakn]

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.

Black Holes Have Lots Of Mass...

[TWX_the_Linux_Zealot]

...but I didn't even know they were Catholic!