question...dark matter and black holes

[hoola]

if dark matter is showing it's existence with gravity effects, wouldn't it be drawn into a black hole along with everything else approaching it, being crushed into the primal constituents of whatever it is made of? If the majority of the universe is of dark matter rather than normal matter, wouldn't that mean black holes are accordingly composed primarily of dark matter?...

[Janus]

Here's the thing, while there is more Dark Matter in the universe than visible matter, it is much more thinly dispersed. For instance, the visible matter of the galaxy is concentrated in the disk of the galaxy, while the dark matter is spread out in a sphere that engulfs the disk. The volume of this disk is so much the larger of the two that the DM in is is very spread out. To give you an idea about how thin, it is estimated that the entire solar system contains only about a small asteroid's mass worth of Dark matter.

 

Since Black holes are usually formed by collapsing stars, there is very little Dark matter in the mix.

 

Another factor has to deal with how visible matter interacts with itself. As visible matter passes by a black hole, it interacts with other matter in the vicinity of the black hole, htis can rob it of energy and cause it to fall into the black hole. Dark matter does not interact with other matter, so when it passes by a black hole, there is no mechanism that can rob it of energy. Without this, unless the trajectory already takes it into the black hole, it will miss and fly right by.

 

The combination of the above factors, black holes are much more likely to formed from visible matter.

 

P.S., I really don't like the term "normal matter", because "normal" is such a relative term. It is just as likely that dark matter is the "normal" matter and the matter that we are made of is the exception.

[ajb]

Black holes should "eat" dark matter in the same way they do standard matter. But due to the no-hair theorem there is no difference as far as an outside observer is concerned.

[hoola]

as far as falling into a black hole, DM reacts perhaps to itself, providing the necessary friction within the confines of it's own substance to lose energy. As dark matter reacts to visible matter gravitationally, a star collapsing into a black hole would have been attracting dark matter since it's birth, just as any other gravitational body. So, wouldn't any star have dark matter already within it?

I was reading on physics world magazine tonight of the difficulty in getting a precise measurement of what they term as "big G", or a true gravity constant. I wondered if the variations could be from interceding clouds of dark matter passing through the tests, skewing the results towards a heavier than normal variety of results...dependent upon the density of the DM at that particular time...

[swansont]

as far as falling into a black hole, DM reacts perhaps to itself, providing the necessary friction within the confines of it's own substance to lose energy.

 

How would it do this? "Normal" matter can radiate electromagnetically, DM cannot.

[hoola]

if we know so little as to the makeup of dark matter, it can't be ruled out that it might have some internal structure property that allows internal friction...

[Janus]

as far as falling into a black hole, DM reacts perhaps to itself, providing the necessary friction within the confines of it's own substance to lose energy.

If it did that, then it would form structures and dense clumps like visible matter does. It doesn't. Its very non-interaction except gravitationally is why it is spread out so thinly.

And, as already posted by Swansont, it has no mechanism to provide friction or to carry away energy. Visible matter has friction because it interacts electromagnetically. It also emits electromagnetic radiation, which carries away energy from the interaction.

[swansont]

if we know so little as to the makeup of dark matter, it can't be ruled out that it might have some internal structure property that allows internal friction...

 

You still need a mechanism to lose the energy. We may not know what dark matter is, exactly, but we know things about what it isn't.

[Schneibster]

We know some things about dark matter, and there are others we don't know. We think we've detected it (I do not agree with the recent declaration that we cannot have) but I don't know if it might signal a difference between inertial and gravitational mass. This is probably the weakest underpinning of the Einstein equation: the equivalence principle.

 

If you want an emotional judgement from me I "believe," snicker, that there will be order and that it will require the anthropic principle; I do not believe that all possible cosmoses can support our form of "life." I believe that our form of "life" will probably not make it out of our local region before the surrounding universe goes over the horizon. Over a long period our several large spirals and hundreds of subgalaxies will evolve and eventually the stars will burn up all the hydrogen; I have not seen late figures on that but IIRC it's on the order of 10¹² years. The universe is so far 1.365 x 10¹⁰ years. It looks like it will "be like this" for a hundred times as long as it has been.

 

If you want to worry about what will happen after the universe is a hundred times as old as it is so far, that is, as if all the universe so far were the first year of an infant's life, and it has all its life ahead of it a hundred years, that is we are the spirit of a single neuron of the barely year-old infant, all humans together, what do you want to worry about?

 

This is perspective about the real length of time.

 

It's like a 1-year-old child being worried about how he'll die after a thousand years.

Edited February 19, 2014 by Schneibster

[hoola]

schneib....if you are referring to me being "worried" about the end of the universe, you are drawing an incorrect inference from the question. It is one more way to examine reality in a similar fashion as any question might allow....whether the question relates to currently operating conditions, or conditions billions of years from now, seems irrelevant...

[hoola]

janus, you say dark matter doesn't form structures? Isn't the "halo" around the galaxy a structure? Aren't the "filaments" of dark matter structures? It doesn't seem to be spread out all that thinly...only more thinly that we can so far observe. Since our EM doesn't react to it much, it seems possible that it reacts to it a little, if only we knew where to look and with what expectation as to the inconsistencies in big G measurements caused by dark matter variations in the small scale, like CMB measurements...if DM is in particle form, then a gradation of particle size should be attained with sufficiently detailed tests...a parallel series of micro tests might reveal some information and add to the overall picture. But how to carry out a small gravity test with a small physical structure would perhaps use mini-black hole pairs as sensing device modus. Their measured relative big Gs as they are separated would reflect a small scale variation of any interleaving dark matter between holes...

to restate the tests,, I see two test types, those of how dark matter does interact with normal matter causing variations smaller than variations caused by (normal) quantum variations, and direct tests from mini-hole pairs of big G...

[Airbrush]

Could dark matter be "ghost" gravity from an overlapping higher dimension? Maybe these dimensions are "pinned" together at the point of black holes?

[Janus]

janus, you say dark matter doesn't form structures? Isn't the "halo" around the galaxy a structure? Aren't the "filaments" of dark matter structures? It doesn't seem to be spread out all that thinly...only more thinly that we can so far observe. Since our EM doesn't react to it much, it seems possible that it reacts to it a little, if only we knew where to look and with what expectation as to the inconsistencies in big G measurements caused by dark matter variations in the small scale, like CMB measurements...if DM is in particle form, then a gradation of particle size should be attained with sufficiently detailed tests...a parallel series of micro tests might reveal some information and add to the overall picture. But how to carry out a small gravity test with a small physical structure would perhaps use mini-black hole pairs as sensing device modus. Their measured relative big Gs as they are separated would reflect a small scale variation of any interleaving dark matter between holes...

to restate the tests,, I see two test types, those of how dark matter does interact with normal matter causing variations smaller than variations caused by (normal) quantum variations, and direct tests from mini-hole pairs of big G...

I said that it doesn't form structures and dense clumps like visible matter does. That is not to say that it doesn't clump at all. The difference is that the clumping mechanism for Dark matter is much much weaker than it is for visible matter. When two particles of visible matter "collide", what really is happening is that their electromagnetic fields are interacting at close range. This can result in the two particles "sticking" together or "bouncing off of each other. In either case, there is a sudden change in the velocity of the particles, When such changes happen to charged particles they emit electromagnetic radiation, which carries away excess energy. Also, since electromagnetic charges can be both negative and positive, the different arrangement the forces involved allows for the construction of structures like molecules.

 

If you try and make dark matter particles collide, the only thing that interacts is their gravity. With no electromagnetic field interaction, they cannot "collide" in the sense that visible matter does. They can be deflected by each others gravity, which will cause a change in their velocity. Such a change does result in some energy being carried away via gravitational radiation. The kicker is that gravitational radiation is some 10^40 times weaker than electromagnetic radiation, so the rate at which energy can be lost this way is very, very slow. So what happens is that the particles pass each other and then separate again moving just the slightest bit slower than they were before. It takes a long, long time before these interactions cause enough energy loss to cause any kind of clumping. And since gravity only comes in the attractive variety, you can't form molecule like structures with Dark matter.

 

What we see in the universe reflects this: large loosely packed DM clumps and tightly packed visible matter clumps.

 

Remember what I said about how thin our own DM halo is; all the DM with the entire volume of the solar system only equals the mass of one small asteroid.

 

As far as EM reacting with it "a little". If that were the case, then it would react electromagnetically with itself "a little", and if it did that, it should have formed denser clumps than it has already.

[ajb]

Could dark matter be "ghost" gravity from an overlapping higher dimension?

It has been suggested that dark matter is something to do with the gravitational effect of branes near to our brane. In sting theory gravity is not constrained to live on branes but can propagate in the bulk. I don't know what the current status of this idea is nor the details of these models.

[MigL]

E8xE8 Heterotic string theory, Airbrush.

[MigL]

To be more specific, from one of my previous posts...

 

"In the E8xE8 Heterotic supersymmetric theory, by Gross of Princeton I believe. each closed string has inherent dimensionality of ten in one direction to describe fermionic fields and sixteen more in the opposite direction ( 26 tootal ) to describe bosonic fields. It does not need renormalization and has gravitons as one of the bosonic field excitations. This E8xE8 symmetry breaks into two E8 symmetry groups, which then breaks to an E6 group and again to the familiar SU(3)xSU(2)xU(1) groups of GUT ( SU(3) ) and standard model Electroweak ( SU(2)xU(1) ). The two E8 symmetry groups are in effect two separate universes connected only by gravity since the other forces only arise after the subsequent symmetry breaks. This second universe is invisible to all other forces except gravity, so we have in effect at least doubled the mass of the universe without any visible other matter, and since the second E8 group does not have to break in the same sequence as the first, it could be composed of heavier particles, like say the supersymmetric equivalents of normal particles, explaning why they have never been observed."

 

There would be a kind of 'pinning' together of these separate universes at black holes because ther continues to be gravitational interaction between them.

 

Also note that this idea is a 'flight of fancy' and certainly belongs in the speculation section !!!

Edited March 2, 2014 by MigL

[Enthalpy]

Stellar black holes are formed by star explosions. How supermassive galactic black holes formed is still unclear - or did this improve?

 

What's the combined mass of the globular clusters (baryonic matter) in the galactic halo? I thought they were heavier than the disk.

 

Further, coalescence can happen just by "evaporating" a fraction of the mass, it doesn't need the mass to radiate. That is, some particles are randomly hotter, others are cooler; the hotter escape the clump's gravity wile the cooler sink to the center.

 

Last time I read about it, one of the theories proposed that dark matter coalesced first, though not very densely, and baryonic matter could then make galaxies. Something like cold versus lukewarm wimps.

 

About dark matter, one should keep in mind that unknown particles (wimps) are not the only candidate.