Dark matter and Dark energy

If some dark matter is normal matter that we can't see, like planets, brown dwarfs etc, then is a black hole classed as dark matter also?
 
We'd budget black holes according to what fell into them. For stellar mass ones this is probably pretty much all normal matter. I don't know if that'd change much for supermassive varieties. Stellar mass ones in the right circumstance and intermediate ones probably count as dark matter MACHOs, supermassive ones we might not strictly count as we tend to have a reasonable idea of where they are and how massive they are. Not sure about the strict definitions there.
 
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dogjones said:
If some dark matter is normal matter that we can't see, like planets, brown dwarfs etc, then is a black hole classed as dark matter also?
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Most black holes probably acquire accretion disks around them. An accretion disk forms outside the event horizon, and is very bright. So most black holes wouldn't qualify as dark matter since we can still see signs of them.
 
What about all the dark matter that went into the hole? Or is our hypothetical dark matter immune to gravity?
 
Not at all. Any dark matter that passes too close falls in. How much actually does fall in is another matter. (sorry, unintentional pun)
 
If our dark matter interacts with gravity, then there might be many more times dark matter falling into black holes than regular matter. Interesting concept.
 
robinson said:
What about all the dark matter that went into the hole? Or is our hypothetical dark matter immune to gravity?
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Did you forget again? The whole point of dark matter is that it gravitates - that's how we know it's there.

So sure, some falls into the hole. But DM is distributed in a spherical halo, so most of it is very far from the center where the hole is. Just like with stars, angular momentum prevents all but a little of it from falling in.
 
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DanishDynamite said:
I've recently read somwhere that at most 4% of our Universe consists of regular matter as we know it. Some 26% consists of Dark Matter and some 70% consists of Dark Energy.

A) How are these numbers arrived at? How is the "Dark Energy" converted to matter?

B) What ever happened to the question of where all the anti-matter went?
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It makes me smile to see you asking such questions :)
 
robinson said:
If our dark matter interacts with gravity, then there might be many more times dark matter falling into black holes than regular matter. Interesting concept.
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I was reading somewhere that according to M-theory the reason why gravity is infinitesimally weaker than the other 3 known forces [EM, weak, and strong] is that it isn't confined to the 4 dimensional "brane" that we exist in and the other three forces are confined to. The idea is that since it diffuses thru higher dimensional space we don't experience it as strongly. If this is the case then it could be that all that extra mass maybe the gravitational effect of matter in "nearby" universes :boggled:
 
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AkuManiMani said:
I was reading somewhere that according to M-theory the reason why gravity is infinitesimally weaker than the other 3 known forces [EM, weak, and strong] is that it isn't confined to the 4 dimensional "brane" that we exist in and the other three forces are confined to. The idea is that since it diffuses thru higher dimensional space we don't experience it as strongly. If this is the case then it could be that all that extra mass maybe the gravitational effect of matter in "nearby" universes :boggled:
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That is unlikely since there are no nearby universes. They are talking about dimensions in this universe.
 
Reality Check said:
That is unlikely since there are no nearby universes. They are talking about dimensions in this universe.
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Both M-theory [especially M-theory] and some interpretations of QM predict multiple "universes". The former describes our cosmos as being a 4 dimensional "brane" suspended within a "higher" multidimensional construct called the bulk and that there maybe many other branes with their own cosmologies. The latter states that the universe continuously produces infinitely branching timelines. Where or not this is actually the case remains to be seen but the fact is that multiple universes is one of the many assertions of the theory.
 
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AkuManiMani said:
Both M-theory [especially M-theory] and some interpretations of QM predict multiple "universes". The former describes our cosmos as being a 4 dimensional "brane" suspended within a "higher" multidimensional construct called the bulk and that there maybe many other branes with their own cosmologies. The latter states that the universe continuously produces infinitely branching timelines. Where or not this is actually the case remains to be seen but the fact is that multiple universes is one of the many assertions of the theory.
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It is more accuate that M-theory has a "landscape" of possible solutions each of which is a possible universes.
Neither the M-theory or QM universes have any interaction with each other.
 
Reality Check said:
It is more accuate that M-theory has a "landscape" of possible solutions each of which is a possible universes.
Neither the M-theory or QM universes have any interaction with each other.
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I understand your point but its not entirely correct [atleast from what I've learned of the two theories]. What I'm saying is that M-theory states that gravitons are not bound to the brane that makes up the observable cosmos. This strongly implies that branes can interact with each other via the force of gravity. According to the "many worlds" interpretation of QM certain interference phenomenon could be considered an interaction of equivalent particles from different universes. The "pilot wave" of a particle's wave function is considered to be the summation of the observed particle's multiverse counterparts.
 
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AkuManiMani said:
I understand your point but its not entirely correct [atleast from what I've learned of the two theories]. What I'm saying is that M-theory states that gravitons are not bound to the brane that makes up the observable cosmos. This strongly implies that branes can interact with each other via the force of gravity. According to the "many worlds" interpretation of QM certain interference phenomenon could be considered an interaction of equivalent particles from different universes. The "pilot wave" of a particle's wave function is considered to be the summation of the observed particle's multiverse counterparts.
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The M-theory branes are restricted to 1 cosmos. I interpret cosmos as the same as universe. I an not sure your implication "that branes can interact with each other via the force of gravity" is correct. My impression is that branes just move about in 11D space.
QM itself has no connection with gravity. Thus the sum over world histories does not include gravity.
 
Reality Check said:
The M-theory branes are restricted to 1 cosmos. I interpret cosmos as the same as universe. I an not sure your implication "that branes can interact with each other via the force of gravity" is correct. My impression is that branes just move about in 11D space.
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Oh, okay; I see the mix up -- sorry 'bout that. Well, I'll rephrase my earlier post then:

According to M-theory the reason why gravity is infinitesimally weaker than the other 3 known forces [EM, weak, and strong] is that it isn't confined to the 4 dimensional "brane" that we exist in and the other three forces are confined to. The idea is that since it diffuses thru higher dimensional space we don't experience it as strongly. If this is the case then it could be that all that extra mass observed as "dark matter" maybe the gravitational effect of matter in "nearby" branes.

I would really like to ask a cosmologist or string-theorist if that hypothesis has been considered or ruled out :)


Reality Check said:
QM itself has no connection with gravity. Thus the sum over world histories does not include gravity.
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Oh, yea I realize that. I just brought it up in response to your statement that there are no other universes. We were just using different definitions for the word "universe". Again, sorry for the mix-up.
 
robinson said:
If our dark matter interacts with gravity, then there might be many more times dark matter falling into black holes than regular matter. Interesting concept.
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Not necessarily. In order to suck up matter, it either needs to be on a direct collision course with a black hole (which will happen, but not very much considering how bloody big space is), or it needs to lose energy in order to fall in. That's easy for ordinary matter to do (ordinary matter can collide with itself inelastically and give off energy in the form of radiation), but not so easy for dark matter to do. So no, black holes don't need to absorb more dark matter than ordinary matter.
 
Ziggurat said:
Not necessarily. In order to suck up matter, it either needs to be on a direct collision course with a black hole (which will happen, but not very much considering how bloody big space is), or it needs to lose energy in order to fall in. That's easy for ordinary matter to do (ordinary matter can collide with itself inelastically and give off energy in the form of radiation), but not so easy for dark matter to do. So no, black holes don't need to absorb more dark matter than ordinary matter.
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maybe it should be called 'slippery' dark matter. ;)
 
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