Is the Mass of Super-Massive Black Holes Factored into Dark Matter Calculations?

[tanzanos]

When it comes to dark matter; Has the mass of the super-massive black holes residing at the core of every galaxy been taken into consideration? Could the total mass of all black holes account for the missing mass in the universe?

 

[nickthrop101]

Dark matter is responsible for the expanding universe, creating a cosmological constant that is greater than 1, meaning a cosmos that is expanding at an accelerated rate. If we just used the black holes mass as the extra mass of the universe, gravity would overcome the positive cosmological constant and start the big collapse

 

[Pengwuino]

When it comes to dark matter; Has the mass of the super-massive black holes residing at the core of every galaxy been taken into consideration? Could the total mass of all black holes account for the missing mass in the universe?

Yes it has, people aren't that stupid.

Dark matter is responsible for the expanding universe, creating a cosmological constant that is greater than 1, meaning a cosmos that is expanding at an accelerated rate. If we just used the black holes mass as the extra mass of the universe, gravity would overcome the positive cosmological constant and start the big collapse

Dark matter, not dark energy. They're different things.

 

[nickthrop101]

But if we consider one to be a condensed form of the other they may be responsible at different times in their existence to act out the same affect

 

[Pengwuino]

But if we consider one to be a condensed form of the other they may be responsible at different times in their existence to act out the same affect

They're completely different phenomena.

 

[BruceW]

About the supermassive black holes: There is other 'not very visible' matter in the universe like dwarf stars, neutron stars, ordinary gasses, black holes, etc which are called MACHOs. Evidence so far seems to say that these MACHOs couldn't possibly account for dark matter.

Also, dark matter and dark energy are two different things.

I think there is a misconception about how great the mass of a supermassive black hole is. Their mass is small, as compared to the total mass of the galaxy.

 

[tanzanos]

I think there is a misconception about how great the mass of a supermassive black hole is. Their mass is small, as compared to the total mass of the galaxy.

How can this be if it is the supermassive black hole keeping the galaxy together and have a mass smaller than the galaxy?

 

[Pengwuino]

How can this be if it is the supermassive black hole keeping the galaxy together and have a mass smaller than the galaxy?

The galaxy is HUGE. Also, in any orbiting system, it actually doesn't matter much how big the central object is when it comes to how much can orbit around that central object. If you have a million solar mass black hole at the center of a galaxy, you could have 1 billion sollar masses worth of stuff orbiting it. As long as it's spread out, everything would still orbit around the one giant concentrated mass that is the super-massive black hole.

The sum of the masses of the planets in our solar system don't really compare to the mass of the Sun, but you can do the same thing with our solar system. You could scatter Jupiter sized planets all over the place and as long as they don't get clumped up or are very close to the Sun, you still could have everything orbiting the Sun.

 

[tanzanos]

The galaxy is HUGE. Also, in any orbiting system, it actually doesn't matter much how big the central object is when it comes to how much can orbit around that central object. If you have a million solar mass black hole at the center of a galaxy, you could have 1 billion sollar masses worth of stuff orbiting it. As long as it's spread out, everything would still orbit around the one giant concentrated mass that is the super-massive black hole.

The sum of the masses of the planets in our solar system don't really compare to the mass of the Sun, but you can do the same thing with our solar system. You could scatter Jupiter sized planets all over the place and as long as they don't get clumped up or are very close to the Sun, you still could have everything orbiting the Sun.

OK; Thanks.

Last Question: Is there a limit to how much matter can be compressed (like in black holes)?

 

[Jack21222]

OK; Thanks.

Last Question: Is there a limit to how much matter can be compressed (like in black holes)?

I've never heard of such an upper limit to a mass of a black hole.

 

[tanzanos]

I've never heard of such an upper limit to a mass of a black hole.

I did not mean how much matter can be ingested but how much compression can matter accept!

 

[Drakkith]

I did not mean how much matter can be ingested but how much compression can matter accept!

Infinite compression. Of course there could be a finite amount before matter turns into something else, but who knows.

 

[tanzanos]

Infinite compression. Of course there could be a finite amount before matter turns into something else, but who knows.

Ah but that is a mystery worth looking into! If a black hole has no limit to the amount of matter it ingests and yet matter is compressed into a singularity at the core of a black hole then we have a problem:

Either matter is infinitely compressible or it ends up elsewhere; like into another universe! I mean theoretically a black hole can swallow whole galaxies.

Does anyone know the limits of compressibility of matter?

 

[Janus]

Ah but that is a mystery worth looking into! If a black hole has no limit to the amount of matter it ingests and yet matter is compressed into a singularity at the core of a black hole then we have a problem:

Either matter is infinitely compressible or it ends up elsewhere; like into another universe! I mean theoretically a black hole can swallow whole galaxies.

Does anyone know the limits of compressibility of matter?

It really doesn't matter. We cannot detect anything past the event horizon, thus as far as we are concerned the "size" of the black hole is defined by its event horizon. The event horizon of a black hole is directly proportional to its mass. If a black hole swallows a mass equal to its own, its event horizon doubles in radius. This means that the volume enclosed by the BH more than doubles. If we take the mass of a black hole an divide it into this volume, we find that the effective density of the black hole goes down as it gets more massive.

To us, outside of the black hole, it does not matter if the mass stops compressing right after crossing the event horizon or continues on towards a singularity. All we can know is that it got larger and more massive.

 

[tanzanos]

It really doesn't matter. We cannot detect anything past the event horizon, thus as far as we are concerned the "size" of the black hole is defined by its event horizon. The event horizon of a black hole is directly proportional to its mass. If a black hole swallows a mass equal to its own, its event horizon doubles in radius. This means that the volume enclosed by the BH more than doubles. If we take the mass of a black hole an divide it into this volume, we find that the effective density of the black hole goes down as it gets more massive.

To us, outside of the black hole, it does not matter if the mass stops compressing right after crossing the event horizon or continues on towards a singularity. All we can know is that it got larger and more massive.

OK now I understand. Thank you for clarifying. Now to ask yet one more relevant question: Since information cannot be destroyed then would I be correct in saying that all information stays at the event horizon? If this so then what is beyond the event horizon is basically nothing?

 

[Lsos]

How can this be if it is the supermassive black hole keeping the galaxy together and have a mass smaller than the galaxy?

I think that's the whole point: the supermassive black hole as well as everything else we see in the galaxy is NOT enough to keep the galaxy together. Something else must be providing the gravity to do so...

 

[mrspeedybob]

Ah but that is a mystery worth looking into! If a black hole has no limit to the amount of matter it ingests and yet matter is compressed into a singularity at the core of a black hole then we have a problem:

Either matter is infinitely compressible or it ends up elsewhere; like into another universe! I mean theoretically a black hole can swallow whole galaxies.

Does anyone know the limits of compressibility of matter?

There is at least 1 effect that prevents the formation of singularities. As the matter compresses it causes greater and greater gravity. Gravity can be modeled as warped spacetime. The more intense the gravity, the more time slows down as compared to an outside observer. From our perspective, outside the black hole, the time needed for a star to collaps to a singularity would be infinite.

What you would observe as you fell into a black hole I don't know.

 

[Drakkith]

There is at least 1 effect that prevents the formation of singularities. As the matter compresses it causes greater and greater gravity. Gravity can be modeled as warped spacetime. The more intense the gravity, the more time slows down as compared to an outside observer. From our perspective, outside the black hole, the time needed for a star to collaps to a singularity would be infinite.

What you would observe as you fell into a black hole I don't know.

I thought that issue had been taken care of by someone already?

 

[tanzanos]

There is at least 1 effect that prevents the formation of singularities. As the matter compresses it causes greater and greater gravity. Gravity can be modeled as warped spacetime. The more intense the gravity, the more time slows down as compared to an outside observer. From our perspective, outside the black hole, the time needed for a star to collaps to a singularity would be infinite.

What you would observe as you fell into a black hole I don't know.

But does not mass require time in order to exist? If time at the core of a black hole is zero then mass cannot exist and thus not even a singularity can exist. Besides if the information remains at the event horizon then so too mass cannot exist even in an extremely compressed state.

How can non mass create such a gravitational effect that nothing can escape it?

 

[Drakkith]

But does not mass require time in order to exist? If time at the core of a black hole is zero then mass cannot exist and thus not even a singularity can exist. Besides if the information remains at the event horizon then so too mass cannot exist even in an extremely compressed state.

How can non mass create such a gravitational effect that nothing can escape it?

Time only slows down for an observer in a frame of reference DIFFERENT from another frame. If you were to fall into a black hole (and survive) YOU would not experience any time dilation for yourself, ever.

 

[n1person]

Various surveys of the Galactic Halo have set upper bounds of the percentage of galactic dark matter that can be found in black holes (and other compact objects):

OGLE: http://adsabs.harvard.edu/abs/2011MNRAS.413..493W
EROS 2: http://adsabs.harvard.edu/abs/2007A&A...469..387T
MACHO: http://adsabs.harvard.edu/abs/2000ApJ...542..281A

Generally speaking, all surveys say less than 10% of dark matter can be found in black holes/compact objects (ranging in mass from 0.0001 to 100 solar masses generally.)

It really doesn't matter. We cannot detect anything past the event horizon, thus as far as we are concerned the "size" of the black hole is defined by its event horizon. The event horizon of a black hole is directly proportional to its mass. If a black hole swallows a mass equal to its own, its event horizon doubles in radius. This means that the volume enclosed by the BH more than doubles. If we take the mass of a black hole an divide it into this volume, we find that the effective density of the black hole goes down as it gets more massive.

To us, outside of the black hole, it does not matter if the mass stops compressing right after crossing the event horizon or continues on towards a singularity. All we can know is that it got larger and more massive.

Assuming, of course, that the Cosmic Censorship Conjecture is correct (which is increasing shaky).

 

[cueball B]

There is at least 1 effect that prevents the formation of singularities. As the matter compresses it causes greater and greater gravity. Gravity can be modeled as warped spacetime. The more intense the gravity, the more time slows down as compared to an outside observer. From our perspective, outside the black hole, the time needed for a star to collaps to a singularity would be infinite.

What you would observe as you fell into a black hole I don't know.

So, if we were to observe a black hole from the outside, would it be possible that we could see an echo of some sort representing the things that have "fallen" in?

If i were to fall into a black hole, would my image be preserved for all eternity, seeing as it would take an infinite amount of time for me to collaps?

(spelling may be of, since English is not my first language.)

 

[vinayjain]

Please tell me if I am wrong about it.....since now reading about a black hole i could have a perception that a black hole nothing other than a star who has got its plasma cooled down and thus created a surface and due to high density it has a very large magnitude of gravitational pull which creates a escape velocity which is even greater than the speed of light...so when anything which is pulled inside a black hole must hit a ground but due to the immense gravitational pull all the subatomic partices gets distorted and hence lead to the body of that object converts into singularity....

 

[Chronos]

A 'singularity' is another way of saying we don't know. We already know that GR and QT do not play well together at Planck scales.

 

[tanzanos]

So, if we were to observe a black hole from the outside, would it be possible that we could see an echo of some sort representing the things that have "fallen" in?

If i were to fall into a black hole, would my image be preserved for all eternity, seeing as it would take an infinite amount of time for me to collaps?

(spelling may be of, since English is not my first language.)

Information cannot be destroyed and it is suspected that all information remains at the event horizon. I suspect that the answer will come from CERN within the next decade.

 

[vinayjain]

Can anyone please tell me something about black hole

Since supermassive black hole has a gravitational pull low in magnitude outside event horizon then what ever matters present there might get compressed and radiate which could be the light spectrum fo black hole...is it possible?

 

[Passionflower]

A 'singularity' is another way of saying we don't know. We already know that GR and QT do not play well together at Planck scales.

Forgive me for asking but how do you conclude we know that?

 

[DaveC426913]

Forgive me for asking but how do you conclude we know that?

The incompatibility of GR with QM is one of the outstanding problems of our time. Two theories, both in their own rights, the most successfully-tested theories ever devised, are not compatible. To try to combine them, particularly when it comes to gravity at small scales, produces nonsensical results (infinities).

 

[Drakkith]

Can anyone please tell me something about black hole

Since supermassive black hole has a gravitational pull low in magnitude outside event horizon then what ever matters present there might get compressed and radiate which could be the light spectrum fo black hole...is it possible?

Low in magnitude? Not sure what you mean by that. Also, the accretion disk around the black hole most definitely radiates, however that is not what is referred to by hawking radiation if that is what you meant.

 

[vinayjain]

Low in magnitude? Not sure what you mean by that. Also, the accretion disk around the black hole most definitely radiates, however that is not what is referred to by hawking radiation if that is what you meant.

no actually i m not talking bout accretion disk but the matters which are present near event horizon in a SMBH they will also radiate due to compression and thus they might also get radiated....

 

[Drakkith]

no actually i m not talking bout accretion disk but the matters which are present near event horizon in a SMBH they will also radiate due to compression and thus they might also get radiated....

I believe that matter is also considered part of the accretion disc. Until it falls inside the event horizon I think it's still part of the disc.

 

[Passionflower]

The incompatibility of GR with QM is one of the outstanding problems of our time. Two theories, both in their own rights, the most successfully-tested theories ever devised, are not compatible. To try to combine them, particularly when it comes to gravity at small scales, produces nonsensical results (infinities).

Producing infinities is nothing unusual in quantum theory, and mathematical methods have been devised to get rid of them.

So I think that does not exclude the possibility that we have not devised a mathematical method to get rid of those infinities if we try to combine GR and QM.

 

[twofish-quant]

The more intense the gravity, the more time slows down as compared to an outside observer. From our perspective, outside the black hole, the time needed for a star to collaps to a singularity would be infinite.

Time doesn't slow down. One way of thinking about what happens is that the pulses that you send out are Doppler shifted so that people at a far distance see the pulses arriving at further and further intervals.

What you would observe as you fell into a black hole I don't know.

Assuming it's large enough so that tidal forces don't matter, you wouldn't notice anything unusual.

 

[twofish-quant]

Producing infinities is nothing unusual in quantum theory, and mathematical methods have been devised to get rid of them.

And those methods totally fall apart when you do gravity.

The problem is that the way that you deal with infinities in QM is to basically expand things out into a power series. At each stage, as you add more terms, you rescale (i.e. renormalize) so that when you do the infinite series you end up with finite values.

(Actually, you sort of cheat, and figure out that all you need are the first few terms, and you sweep the rest under the rug.)

This doesn't work with gravity. The problem is that gravity produces gravity. If you work with EM and imagine two electrons exchanging a photon, there is a tiny correction as that photon generates more photons, but it's small enough so that you can sweep under the rug.

With gravity, this doesn't work, because gravity generates gravity which generates more gravity which generates more gravity, and soon you have infinities popping up all over the place.

This is a terribly oversimplified version of what happens, and corrections are appreciated if I got something wrong.

So I think that does not exclude the possibility that we have not devised a mathematical method to get rid of those infinities if we try to combine GR and QM.

Most people think that no such method exists, and the reason we have all sorts of infinities while the world works is that some point in the real world you can chop off the power series because the rules change.

 

[Passionflower]

Assuming it's large enough so that tidal forces don't matter, you wouldn't notice anything unusual.

Would we see the light of the stars behind the black hole? And if so what would the redshift show the closer we get to the singularity?

 

[Drakkith]

What do you mean by "gravity generates gravity"?

 

[twofish-quant]

What do you mean by "gravity generates gravity"?

This is quantum field theory massively simplified.

You have two electrons. You ask what happens if those two electrons exchange one photon. Then you ask what happens if the electrons exchange two photons. Then three. You end up with a nice series of Feynman diagrams which you add up.

This works because photons are not electrically charged so that photons don't generate more photons (easily, yes I know about loop corrections, I'm vastly oversimplifying here).

Now let's try the same thing with gravity. Suppose we have two electrons, we calculate what happens when it exchanges one "graviton" with each other. The problem is that "gravitons" have energy, which means that they have mass, which means that they generate gravity. Gravitons having energy and therefore mass will attract each other, which means that they you have to take into account "gravitons" exchanging "gravitons" with each other. And those particles have energy therefore mass and...

So rather than having one infinity that you can deal with, you have infinities all over the place. The more corrections you put in, the worse your situation is. That means that the mathematical approach you use for QED, just won't work with gravity.

The other thing is that people that are much smarter than I am are of the opinion that this problem is not just because the mathematical approach is wrong, but that there is something basically fundamental about GR that makes all of these infinities pop out.

 

[twofish-quant]

Would we see the light of the stars behind the black hole?

I have to think about that, but once you cross the event horizon, most of the stars would look normal. You can't see into a black hole, but you can see out of it.

And if so what would the redshift show the closer we get to the singularity?

Off the top of my head, you wouldn't see a redshift for the things going into the black hole.

I have to warn you that my general relativity is very basic. I'm not a black hole expert, and my knowledge comes from thinking about what happens when a supernova turns into a black hole, so I haven't thought much about what things look like inside a black hole.

 

[Passionflower]

So rather than having one infinity that you can deal with, you have infinities all over the place. The more corrections you put in, the worse your situation is. That means that the mathematical approach you use for QED, just won't work with gravity.

Yes the mathematical approach you use for QED does not work with gravity. But how does that imply that it is impossible for someone to devise a method that does work?

 

[DaveC426913]

Yes the mathematical approach you use for QED does not work with gravity. But how does that imply that it is impossible for someone to devise a method that does work?

The claim is not that is it "impossible" for someone to devise a method, the issue is that no one has.

i.e. with our current understanding of QM (which has been tested extensively and passed with flying colours) and our current understanding of GR (which has been tested extensively and passed with flying colours), we cannot reconcile the two.

As he said, they do not play well together.

 

[twofish-quant]

The claim is not that is it "impossible" for someone to devise a method, the issue is that no one has.

Most mathematical physicists that I know are of the opinion that it is in fact mathematically impossible to reconcile classical GR and quantum mechanics, and that the problems that people have using standard QM techniques on GR are not a "lack of trying" problem but rather a "this is mathematically impossible" problem.

I don't understand the math myself well enough to explain why they think this, but if someone else doesn't chime in, I'll dig into the papers and try to come up with a "why GR is non-renormalizable cartoon" post.

with our current understanding of QM (which has been tested extensively and passed with flying colours) and our current understanding of GR (which has been tested extensively and passed with flying colours), we cannot reconcile the two.

The problem is that if you combine the two, you get infinite series that diverge. The good/bad news is that they diverge at energies which we cannot observe, which means that you can try to deal with the problem by chopping the infinite series once the energies get too high.

This gives you string theory or loop quantum gravity.

So the consensus seems to be that the real theory looks like QM and looks like GR, but it isn't QM or GR.

 

[twofish-quant]

Yes the mathematical approach you use for QED does not work with gravity. But how does that imply that it is impossible for someone to devise a method that does work?

It doesn't. But there seems to be a strong consensus among mathematical physicists that GR is non-renormalizable, which is to say that there are so many infinities that pop out, that no mathematical method can get rid of the infinities. The solution is to come up with a theory that looks like GR but isn't (i.e. string theory).

Now, since I don't specialize in quantum gravity, I can't explain why the quantum gravity people think it can't be done. Hopefully someone that does understand the field better than I do can chime in, and if not, I'll go through the papers and try to come up with a cartoon explanation.

 

[twofish-quant]

Actually the wikipedia article explains the problem...

http://en.wikipedia.org/wiki/Quantum_gravity

To summarize in a cartoon way. You can get rid of an infinity by dividing it by an infinity and setting infinity/infinity to a finite number that we can observe. With QED, there are three infinities so that we can do that.

For gravity, it turns out that there are an infinite number of infinities. So if you try that trick it turns out that you have to set an infinite number of numbers to finite values, which we can't do since that requires an infinite number of observations. All of the work in quantum gravity has been to try to turn that infinite set of fudge factors to a finite set.

 

[DaveC426913]

Most mathematical physicists that I know are of the opinion that it is in fact mathematically impossible to reconcile classical GR and quantum mechanics, and that the problems that people have using standard QM techniques on GR are not a "lack of trying" problem but rather a "this is mathematically impossible" problem.

I didn't mean to suggest that it was a problem just waiting to be solved.

I think the implication is that our understanding of GR or QM or both is broken, and they won't be reconciled until we understand them better.

 

[twofish-quant]

One thing that I've found out is that things are easy if you don't know why they are hard.

The reason that passionfruit's questions are interesting to me is that I was asking the exact same question in 1989 when I was a junior physics major. I knew enough QM and GR so that it *seemed* really simple to mix the two, and so I spent the next two years learning enough basic quantum field theory and GR to try to mix the two.

I remember when as a first year graduate student, I finally understood enough to realize why the problem was so hard, and why the easy solution wouldn't work. It was an "anti-eureka" moment, and the first of many.

One huge disadvantage that I had was that I lived in the "dinosaur era" before the World Wide Web existed. That means no google, no paper databases, no discussion forums, no wikipedia. We had USENET and e-mail. The good news is that with all of these tools, it should be a lot quicker to get people to the "anti-eureka" moment.

Something that I find funny is the Eureka myth. People always talk about that brilliant flash of insight which let's you realize how things work. The funny thing is that people don't talk about the reverse situation. Sometimes you get hit by lightning and the brilliant flash of insight is that what you've been working on the last few years just won't work.

 

[vinayjain]

When it is said that gravity cause gravity is it like magnetic field produces magnetic field ?

Please clarify

 

[Drakkith]

When it is said that gravity cause gravity is it like magnetic field produces magnetic field ?

Please clarify

See post # 37 by Twofish.

 

[phinds]

Something that I find funny is the Eureka myth. People always talk about that brilliant flash of insight which let's you realize how things work. The funny thing is that people don't talk about the reverse situation. Sometimes you get hit by lightning and the brilliant flash of insight is that what you've been working on the last few years just won't work.

Perhaps it's just semantics, but to me that's STILL a Eureka moment. Granted, you haven't discovered how something DOES work, but you have discovered how something doesn't work and that's a step of knowledge. I guess my point is that when you discover a new piece of knowledge, that's a Eureka moment, even if the knowledge is the certainty that something WON'T work.