Dark Matter and Black Holes

I don't think there is a known mechanism for dark matter (DM) to form stars or black holes. The reason is that DM interacts extremely weakly with ordinary matter (or even with other dark matter particles), i.e., it can go right through it without interacting. Hence, there cannot be the friction losses that cause swirling masses of gas to collapse gravitationally.

For the same reason, DM isn't dragged into black holes (BHs) on a large scale, but will just circle the hole. Only DM particles that happen to have a trajectory that take it very close to a BH can get trapped and fall in, but without radiating anything, because there is no friction.

Jorrie

As I understand it, the point of dark matter is that it only interacts with regular matter through the gravitational force.

I think that a charged particle accelerated near the speed of light emits photons but I don't think that is the case for uncharged particles, which is what dark matter is supposed to be.

The only effect I can see dark matter producing is an effect on gravitational waves produced by a star orbiting a blackhole. These gravitational waves may alter the interaction of the ordinary matter as it falls into the black hole since gravitational waves are essentially oscillating alternating curvatures in spacetime. That change in the interaction of ordinary matter may be observed.

Is not the gravitational attraction in both directions,from and to normal matter? If so, why would it not be mutually attracted by the black hole gravity?If it interacts through gravity, it is not immune to the pull of a black hole, is it? Or Is it?

Because in order to fall into a black hole you need your orbit to degrade. In other words you have to lose enegy, unless you hit it dead on, which is hard to do in the vastness of space. If you're a particle that doesn't interact with anything in the usual ways, it's hard to lose energy, so you end up stuck in orbit.

So what you are saying is if there was a large mass of dark matter, ordinary matter, such as a star, would orbit around it, but it would not reciprocate,but remain rock-steady as the matter orbited around it? It really doesn't make sense that the gravity is one-way.Perhaps dark matter does not really exist, and perhaps there are other things that can warp space-time, or perhaps space time is not truly uniform everywhere.Perhaps the gravity of a galaxy generates it's own field which amplifies gravitational effect. If object A aligns with object B, in relation to object C, does object C feel a combined effect of the two objects? If so, look at all the possible interactions in a galaxy.Could this amplifying effect account for "dark matter"?

Jorrie and Roger say that there is gravitational (mutual) attraction between ordinary matter and dark matter (DM).

[It is supposed that DM "exist" because of the apparent lack of matter: The ordinary matter (everything that is composed of fermions -i.e. quarks & leptons-) seems not to be enough in order to explain the observable gravitational interaction between the several parts of matter (stars, galaxies, clusters e.t.c.) in the universe. So, in a first place, the existence of the DM seems to be a necessity.]

They just say that it is not easy (or it is almost impossible) for the DM to fall into a BH, due to the fact that it cannot emit (or lose) energy, hence coming (orbitaly) closer and closer to the BH and finaly fall into it.

That's all.

Hmmm. Roger, I know what you are saying, but at the same time, matter (or...) being drawn towards the event horizon picks up extreme gravitational energy and converts it into tremendous kinetic energy, which is the source of X-rays etc from super heated gases rotating at higher and higher speed around the black hole and on their way thru the horizon.

Generation of gravitational waves* would presumably cause the orbits of both the dark matter and the ordinary matter to decay? But shouldn't we expect interactions due to more ordinary (localised) tidal forces to have more effect (than wave generation) in the regions further from the hole, and this would be more effective in determining the mass that arrived in the hole? But that would still be rather small compared with the decay of normal matter (there might even be a slight reduction in the mass of ordinary matter falling into the hole - though I don't imagine this would be detectable, nor would it fully compensate the [already relatively small] additional amount of dark matter).

However, to my mind, the most interesting connotation of this question is that its consequences (the masses and frequency of occurrence of black holes) would potentially clarify whether dark matter emits a form of quasi-radiation that does not interact with our form of matter? Comments?

*BTW, given the large gravitational effect of the hole itself, I doubt it would ever be possible to resolve the gravitational effects of the relatively small amount of dark matter in the region around the hole.

P.S. Assuming that dark light does exist* (interacts with dark matter but not with us), I still think that the dark matter will decay at a rate comparable with ordinary matter.
*Given the expected relative masses and that the universe seems to be addicted to symmetries and to number theory, I would be unsurprised if there turned out to be three (maybe more) coexisting types of matter, each dark to the other two (but bright to its own kind).

Jorrie, it almost sounds as if you are describing neutrinos...very weak interaction with matter, going right through w/o interacting, etc. You don't suppose DM is massive clouds of static neutrinos? Well, the 10 ^nth power of neutrinos emitted by all the stars have to go somewhere, as does all the radiation emitted... And while you're explaining that, what is the space of the expanding Universe expanding into? Is the Universe a closed system? Can energy leak out of the system? Ouch. My head!

Neutrinos were a candidate at one time.

Suppose that there are irregularities in space time that formed in the beginning,then clouds of gas would naturally fall into them,starting the formations of galaxies, etc.The deformations would remain after the galaxy formed, giving the appearance of the effect of invisible matter causing the extra deformation of space time. We have only sampled a minute amount of space time, even the observable universe is only a speck,so how can we be certain the space time is really uniform and homogeneous in all directions? A blemish in the "grid" of space time would eliminate the need for Dark Matter.IMHO

Hi Jorrie,

If the DM is gravitationally attracted to the black hole, then the DM particles would also become superheated. Would they not collide with ordinary matter, causing the ordinary matter to radiate? Wouldn't the ordinary matter change the course of many of the DM particles, and direct them into the black hole? So are you saying that DM and ordinary matter don't collide?

S

Perhaps a better name for DM would be "Naked Gravity", because that is all we can say about it.It does not react with itself or other matter, yet it exerts a warping effect on space time, just like gravity.Can gravity(warped space time) exist without mass causing the warpage, or could space time itself actually be imperfect from birth?

If space time is actually warped in and of itself,the formations of galaxies near DM would be a natural offshoot of this, with matter accumulating in these "indentations".

The attraction of matter to these points would increase the warpage even further,with a black hole forming at the center.Black holes are very closely related to every galaxy,with a very startlingly consistent percentage of the galactic mass (.1%) being the norm and dominant percentage.If the black hole formed first, all subsequent matter would be affected not only by the black hole, but the combination of it's mass and the "birth defect" present from the near beginning.

-----------------SSB________________________________

How's that for consistency?
"because that is all we can say about it" followed by the statement that
"it does not interact with itself".
Actually, in terms of observation, all we can say about it at this stage is that

We can't see it, but we deduce its presence because its gravitational effect is necessary to balance our cosmological observations

As it happens, it also fits nicely into high-energy quantum mechanical theories. However, there are gaps in our understanding that extend from somewhat before the conditions where we would expect non-gravitational interaction between dark matter and our kind of matter. Be that as it may, the expectation is that there will be at least one family of dark matter that interacts between family members. This would obviously require a different interaction mechanism to our photon; but I for one have no idea whether the causal relationships between the dark matter and its quasi-photon bears any resemblance to what we see with our photons.

You're talking like this "dark mater" theory is the reality.Are you even sure if this "dark matter" really exists? The entire theory is based on quantum mechanics and the theory of relativity. How can a scientist repel the idea that a particle or galaxy moves faster than the speed of light simply because it doesn't fit the theory? Try to document yourself on the "Electric universe", which by the way explains many things about this space arround us, that can not be explained by quantum mechanics and the theory of relativity. Stating that there is "dark matter in the universe" is like saying that you have absolutely no freaking idea of what's out there. But no scientist would say that, it's bad for the credibility. Ussualy people tend easily to believe a big lie for a small lie.Why to people tend to forget that it is only a theory, NOT the reality, and the theory becomes a belief. We get so convinced of the theory that it becomes hard to accept different perspectives.

Maybe dark matter is just ordinary matter in a parallel universe and the gravity just "leaks through".

To discuss the question asked in the beginning, we must postulate the existence of dark matter. I suggest that discussions calling this into question are the subject of another thread. Having taken the leap and assumed we have dark matter, the answer to the question depends on what we believe the dark matter consists of. I confess to not being up-to-speed on the latest theoretical developments, due to making my living outside of the world of physics, but back in the day when I was still in the field there were two schools of thought. One held, as was implicit in one of the replies, that DM consisted of particles that have no mass but react gravitationally with normal matter. This was called the, "Weakly Interacting Massless Particles" theory. Others hewed to a more conventional theory that the missing mass was contained in undetected brown dwarves and the like that were in the halos of galaxies, called the, "Massive Compact Halo Objects" theory.

The answer thus depends on whether you are a WIMP or a MaCHO.

You confess to '....living outside the world of physics,', ostensibly for occupational purposes. Your job must be very interesting indeed.

To postulate something a little different....

It appears that it is always assummed that black holes are "holes" that matter is sucked or falls "into". What if black holes are actually an extremely dense mass that reacts in standard fashion with regular matter? Matter is then drawn "onto" rather than "into" a black hole. Since the extremely dense gravity prevents the escape of photons, a black hole camouflages itself against the darkness of space. What evidence shows that it must be a hole rather than a body?

As a star spends it's fuel through fusion, it becomes denser. Is it not plausible that what we are seeing is an undetected element with an extremely high atomic weight? As matter is drawn to it, the new matter is colapsed by gravity into the element in question, effectively reproducing or growing the mass...

Fire up that new collider, let's try and make a black hole here on earth. :)

-Guest 2

The problem with this problem is that we don't know enough about dark matter to be certain of the answer. I believe that the consensus is that there is a lot of "dark energy" in the universe, and my assumption is that this interacts with dark matter - possibly in a manner akin to the way we interact with light. So my take on this is that the chances are that dark matter would disappear into a black hole in a manner rather similar to ordinary matter; but it won't generate X-rays that we can detect, but would generate dark-radiation X-ray equivalents instead. Our problem is that we won't detect the dark x-rays (there could conceivably be interactions at the highest energy, but these would be orders of magnitude less frequent than we would currently know how to discriminate). So the only way we could tell this was happening would be if/when we accumulate enough black-hole data to conclude that they are heavier or more frequent than could be explained by the annihilation of visible matter.

How much would we know of the universe if everyone were born blind? All matter would be invisible to us.All matter would be dark matter.In reality, it would not be, but would seem to be. We may be blind to a spectrum of energy that our best instruments cannot discern. Like radio waves, before radio was invented.They always existed, but no one knew about them, or how to use them.I am sure the substance we call dark matter will one day become visible to an instrument that has not even been imagined yet. We cannot see the wind, but we can see the effect of the wind; so it is with dark matter at the present time.Dark matter may be "naked" gravity, with all of it's mass stripped away in the big bang,before all of the forces united, or the remnants of a black hole so dense that it actually ripped through and exited space time as we know it , leaving behind only part of it's gravity: it's ghost. The smallest particle is closer to us than the largest object in the universe, and we have far to go and much to learn. --------------------------------------------------------------------------------------------------------------------------------------------------------------------Reality is only an illusion brought on by sobriety. HTRN

Is gravity a wave?If so, can a standing wave be created with gravity,which could give the illusion of matter (extra deformity of space time) where none exists?

The standing waves of light (that we are accustomed to) are produced by virtue of light being reflected. These particular reflections are possible because of interactions with charged 'particles' in the reflectors. No equivalent interaction is known or predicted for gravity - therefore, no gravitational reflections and no gravitational standing waves (unless you regard the entire universe as one).
However, I wouldn't like to state categorically that we will never need a new physical model - nor that this will definitely not allow of gravitational reflectors. (At which point, hyper-travel becomes a theoretical possibility...)

Cannot colliding waves create standing waves if of equal amplitude and frequency, but moving in opposite directions? No absolute need for a reflected wave, is there? With the proper spacing of massive objects, could gravity waves be guided around an object,creating a space that is invisible to gravity? Similar research has been able to do this in the lab with water waves, opening the possibility to make off-shore platforms and even islands invisible to Tsunamis.Why not gravity waves?

Tsunamis involve waves being focused by a discontinuity at the bottom surface of the sea. Again, no such mechanism is known for gravity - other than gravitational distortions themselves (and there are quite severe constraints on their geometries).

It's true that two radiators of similar frequency at different positions will generate standing waves - so the amplitude can be twice that of either of the radiators. The place you could get recirculating gravitational waves is near the event horizon of a 'black' hole - waves circulating around the circumference. But you would need to have something remain in place for a cycle to get more than a single refocusing - and the waves will only be focused circumferentially, so the "focus" will be much less intense than the original source.

If stereo speakers are out of phase, the sounds cancel out. Headphones with noise canceling technology are available, using the same principle of cancellation.The same should apply to light and gravity.In phase waves amplify, out of phase cancel.Suppose dark matter is merely a region around a galaxy where light(visible and otherwise) is canceled out by out of phase components?----Just a wild thought...HTRN............................. "I SEE! " said the blind carpenter as he picked up his hammer and saw.-----------------------------------

The analogy to a balloon has been made to represent the space-time universe as we currently understand it, with matter causing a deformation, or curve in space time. Using this analogy, take it a little further:If you press your finger into a balloon, the inside pressure increases, and the overall diameter has to expand to equalize.Imagine trillions of fingers(matter) stretching space time, each on a "local" scale, but having an effect on space time as a whole.Objects would tend to move away from each other by this overall expansion, as well as be attracted to each other by the curvature of local space time.The local space time is stretched, so does this mean that it takes less mass to curve it further?The stretched space time "fabric" has to come from somewhere.Does the fabric of space time become "weaker" as mass increases? Could this give a false impression of extra matter where there is none? When we look at our galaxy, or any object in space, we are looking back in time.We have to speculate what is going on at the present time.The center of our galaxy is much further back in time than the outer spiral arms, so the gravitational effect from the center took billions of years to affect the outer arms.If the center of our galaxy suddenly disappeared, it would not be apparent to us for billions of years, assuming gravity travels at the speed of light. We are not getting a real time snap shot of our universe, and probably never will.We really have no idea what is actually happening,only "yesterday's news". IMHO-----------------------------------HTRN------------------------------------- I was once hooked on placebos, I was going to quit but my doctor said it would not do any good.I am now taking the real thing and trying to wean off.

The further away we look, the faster the universe seems to be expanding. Could it be that it is because we are looking further back into the past, when the universe was expanding faster? How do they allow for this factor in their calculations of expansion? ---------Curious----

Black holes are the fictional equivalent of dark matter and dark energy, so when people actually figure out that DM and DE do not exist they will have a backup fictional theory available to account for all the missing mass.

Let us speculate that they exists, how would you know? According to theory light itself fails to escape. Any energy emitted at the event horizon would A) fall into the black hole or B) take infinity to reach you due to gravitational time dilation. Also to imply there is an escape velocity even if greater than light means any object including light could leave the black hole, just not escape, that is they would go out, stop and fall back. The Earth has an escape velocity. I can jump of its surface, just not escape its gravitational pull, I fall back.

Einstein himself argued against applying his theory to singularities until the day he died. he himself did not believe they existed. The only know solution to his field equations requires the universe to be devoid of all matter Ric = 0. This in effect means that there exists no energy, no matter, no gravity, nothing.

http://www.sjcrothers.plasmaresources.com/BB.pdf