Dark Matter

[C1ay]

Just thinking out loud here....

 

Cosmologists calculate that there must be vastly more matter out there than we can physically observe. Many stars near the center of many galaxies have much higher velocities than they should have indicating a gravitational force we cannot see. Is it possible that the center of every galaxy contains a massive black hole and that these enormous masses are responsible for the vast quantity of matter that is unaccounted for? Are these billions of black holes a sizeable portion of the dark matter we are looking for?

[coldcreation]

Just thinking out loud here....

 

Cosmologists calculate that there must be vastly more matter out there than we can physically observe. Many stars near the center of many galaxies have much higher velocities than they should have indicating a gravitational force we cannot see. Is it possible that the center of every galaxy contains a massive black hole and that these enormous masses are responsible for the vast quantity of matter that is unaccounted for? Are these billions of black holes a sizeable portion of the dark matter we are looking for?

 

This subject has been discussed in a number of other threads, but no problem, let's continue...

 

The standard models require a linear redshift-distance relation. Furthermore, this situation requires the introduction of non-baryonic matter (a hypothetical form of matter which would not be made of electrons, protons, neutrons, quarks, etc.) located between clusters of galaxies.

 

It is a well-known fact that much of the mass in the universe is invisible to our telescopes. Planets, rocks, asteroids, brown dwarfs, often called “massive astrophysical compact halo objects” (MACHOS), objects with very little surface luminosity. But these objects may be insufficient to appease the necessary constraints for ? to equal (anything close to) 1. This has led to a heated frenzy in search for some elusive form of unidentified matter—as yet unknown.

 

New physics is required to explain this hypothetical form of matter. Its existence can be confirmed neither experimentally nor observationally. Some suggested candidates are black holes, or “weakly interacting massive particles” (WIMPs) such as axions, supersymmetric gravitinos and photinos, or massive neutrino-like particles. These exotic particles and some hypothetical forms of MACHOS are theoretical extrapolations that are far beyond experimental verification capabilities.

 

As we see, the pandemonium of the missing mass/flatness problem is in reality much more complex and much more serious than it sounds. It is directly related to initial conditions, the unknown mass-energy density of the universe, the rate of expansion or Hubble law, the redshift-distance relation, and the geometric curvature or topological structure of the universe at large. An amazing amount of literature is available on this problem: testimony to its importance. It will undoubtedly demand more attention as this story (thread) unfolds.

 

It gets worse...

 

Coldcreation

[C1ay]

This subject has been discussed in a number of other threads, but no problem, let's continue...

 

The standard models require a linear redshift-distance relation. Furthermore, this situation requires the introduction of non-baryonic matter (a hypothetical form of matter which would not be made of electrons, protons, neutrons, quarks, etc.) located between clusters of galaxies.

Perhaps you misunderstood my thoughts. I wasn't talking about matter between galaxies but blackholes at the core of all galaxies. I'm not particularly suggesting that blackholes are made of dark matter but they are by definition dark and a vast quantity of them would account for a vast quantity of matter, matter that would otherwise be visible if it weren't beyond the event horizon of the black hole.

[infamous]

I'm not particularly suggesting that blackholes are made of dark matter but they are by definition dark and a vast quantity of them would account for a vast quantity of matter, matter that would otherwise be visible if it weren't beyond the event horizon of the black hole.

I have often wondered about this same posibility C1ay. If black holes exist, and it appears that the evidence is mounting in favor of this theory, then it would stand to reason that an incredible amount of matter is locked up inside these objects. If the dark matter, missing from our view, is contained within these objects, this might explain the observed discrepancy in cosmological calculations. However, my own take on the question of black holes is lacking definition. By this I mean to say that, in my opinion I don't logically view black holes as eternally black. And saying this, I'm not referring to Hawkins radiation reducing the size over time. I suspect that there remains a limit to the size a black hole can achieve. Recognizing that I'm certainly no expert on the subject I can only justify my position by making the point that until we can scientifically examine a black hole with laboratory precision, there exist no experts on the matter.

[coldcreation]

Perhaps you misunderstood my thoughts. I wasn't talking about matter between galaxies but blackholes at the core of all galaxies. I'm not particularly suggesting that blackholes are made of dark matter but they are by definition dark and a vast quantity of them would account for a vast quantity of matter, matter that would otherwise be visible if it weren't beyond the event horizon of the black hole.

 

 

The dark matter problem on scales compatible with galactic nuclei is inextricably attached to the dark matter problem on the large-sclae (at high-redshift). They overlap.

 

We know that dark matter exists in the form of faint objects—collectively referred to as brown dwarfs. These are low luminosity objects that are very difficult to detect because they are very weak emitters of electromagnetic radiation, e.g. low mass stars that no longer burn hydrogen into helium. Other examples of dark matter include planets, comets, asteroids, rocks, dust, and gas.

 

From application of the viral theorem to the rotational curves of galaxies and clusters, estimations of the dark matter are about ten times that of visible matter. This dark matter is thought to be responsible for the binding of galaxies and galactic clusters (Longair 1993). We are still 2 orders of magnitude less than the critical value (for the favored ? = 1 model).

 

SMBHs in galactic nuclei are inferred by rotational curves: the velocity of stars around the galactic core, and at any distance. The question remains: can we estimate the mass of objects by studying the velocity of objects in orbit around an unseen companion. My answer is no. No, because I believe that objects can move faster or slower than would otherwise be permitted by the centrifugal force/mass/distance relation.

 

In other words, even if two bodies, e.g., the moon and the earth, were to stop in there tracks, they would never collide with one another. Each remains in its gravitational well (I should elaborate, but no time now).

 

Finally, we can only conclude that rotational curves cannot by implication, indirectly, infer the mass of companion objects.

 

Postmortem (on large-scale): Ordinary matter refers to elements composed of protons, neutrons and electrons. Visible forms of matter, stars and galaxies, account for less than 1% of the critical density. Even with the additional baryonic dark matter (brown dwarfs, planets, gas, and their constituent protons, neutrons and electrons) the missing mass problem is still as real as ever—a dazzling reminder in dark times of what cosmological dramatists do best.

 

Coldcreation

[coldcreation]

rotational curves cannot by implication, indirectly, infer the mass of companion objects.

 

Coldcreation

 

Proof that centrifugal force is not responsible for the occurrence of stable systems come from the fact that all galaxies are not in a state of rotation sufficient to account for the observed flattening of the galaxies. There are gravitating systems in which the random velocities of stars are insufficient to prevent the galaxy from collapsing. Elliptical, spherical and some irregular galaxies do not possess the necessary velocities of rotation required to maintain equilibrium, yet they do not fly apart or collapse.

 

Other spiral galaxies and barred spiral galaxies appear to me rotating to rapidly to maintain stability. The simple representation of rotational flattening cannot be correct. This has led to the haunting themes of non-baryonic dark matter, hidden dark energy and supermassive black holes—the sole means by which the gravitational pull of stars could possibly hold the galaxy together. This dramatic justification is unfortunate because the new-physics required to clarify both SMBHs and non-baryonic dark matter not only deviates from conventional experience but clearly violates the known laws of nature—all of them.

 

Cold Creation explains the observed stability of self-gravitating bound systems in a natural way, and in conjunction with the laws of nature—all of them.

 

Coldcreation

[cwes99_03]

I'll throw my hat in the ring to add a little bit of info that I think coldcreation might be leaving out. I admit first though that as a general physicist I don't know a great deal about the entirity of this subject.

 

Colcreation mentioned the theory of black matter as the "stuff" that holds galaxies together. I had heard this before, but never as a reason for why Elliptical, spherical and some irregular galaxies do not fly apart, though in retrothough on the subject, I certainly understand this theory. But how much do we know about the formation of galaxies anyway.

 

Anyway we have two different threads being discussed here.

 

1) Dark matter, it's theorized origins and existence.

2) black holes (be they super massive or not) and whether they can possibly explain the theorized amount of dark matter in the universe.

 

The first, is quite interesting, though as cold pointed out, all theoretical, as there is no current method for measuring for the material since we can't see it. I tend to believe that means that we are barking up the wrong tree, and that if we can't see anything anywhere in the spectrum that means it most likely doesn't exist as it would cause interference with the light that passes through or near it. But as I said maybe I missed something in my readings that would explain why it doesn't have to "mess" with our view of the rest of the spectrum of light out there.

The theories for the existence of dark matter, I believe, are based upon the idea that there has to be something holding irregular galaxies together, and the speed with which spiral galaxies are rotating (as many appear to rotate much faster than Kepler's laws would allow, taking into account the theorized size of the black hole.)

 

Now, I would like to revisit my point about how much we know about irregular galaxies. As it took 13 billion years or so for us to reach this point, how long does it take to form a beautiful spiral galaxy. We can theorize, but never know without watching what happens over the next oh billion years. Current theories are based on the great quantities of galaxies that are out there, what they look like, how old we think they are based on what stars are contained in them, and what environment they are in.

 

Empirical evidence seems to point towards the center of all galaxies to be some sort of black hole, a SMBH in the case of our galaxy. Their masses can be calculated based upon the spectral red-shift of particle accretion disks spinning around them, thus calculating the speed of these particles, and thus calculating an approximate size (mass) of the black hole.

 

So to answer Clay's question, I would have to say that black holes and dark matter have nothing to do with each other. Black holes exist in the universe even according to dark matter theorists. They simply note that black holes can't explain everything about the make-up of the different galaxies.

 

Not really sure though where MACHOs and WIMPs come into this discusison though. I remember MACHOs as star clusters outside of the plane of the galaxy, though I don't know if they are passing through or roatating with the galaxy out of its plane.

 

Dare i throw a wrench in? I have recently begun wondering about the effect of the EM fields passing through the great black. How we might measure their effect, if there is any, on the gravity of objects? Namely, if I created a great enough concentration of pure light , would it be capapble of (being massless) a gravitational field. Honestly I have not put any thought into whether that is a viable question. Just something that sticks in my mind and won't go away until I take the time to find an answer.

[cwes99_03]

Might I also ask a question about dark matter and the aether? Well, maybe another time.

[CraigD]

Last month’s Scientific American had a nice article about galaxy dynamics, ”Ripples in a Galactic Pond” (subscription required for full article). Summarizing, the author suggests, based mostly on large computer simulations, that the structure of galaxies changes over time more dramatically than is commonly believed, with features like arms and bars appearing, disappearing, and reappearing like features in a ripple pond. No new or surprising Physics in the article, just complicated applications of conventional theory.

 

I agree with coldcreation that current theories explaining the larger-than-galactic-scale structure of the galaxy are a mess, what with the near 1 Hubble constant, an apparent repulsive “cosmological constant” force, etc. While whatever’s behind these problems are sure to have some effect on them, I’m still hopeful that an understanding of the structure of galaxies is possible with old Physics and more accurate simulations. Despite my optimism, as an old (and thoroughly exhausted) hand at gravitational simulations, I think it’s important to maintain an awareness of the limitations and potential chaotic behavior of such systems. In the absence of a practically calculable solution for the n-body problem, ones trust in gravity simulations should be guarded.

[C1ay]

Perhaps I used the wrong title for this thread. I was not suggesting anything that would support the theorized quantity of dark matter. What I was thinking is that maybe there's a whole lot more black holes out there than we think and maybe that's why it seems there must be all this alleged dark matter to make the current model work. When we look at things like the Hubble Deep Field the observation really tells us nothing about the quantity of supermassive objects that may lie at the edge of our depth of view. Just how massive could the oldest blackholes be and how many of them could there be. Could these numbers be high enough that current estimates of the quantity of dark matter are significantly off?

[damocles]

In other words, even if two bodies, e.g., the moon and the earth, were to stop in there tracks, they would never collide with one another. Each remains in its gravitational well (I should elaborate, but no time now).

 

(scratches head over that one.)

 

Am I correct in in thinking that all our guessing and speculation of what is wrong out there in the great beyond; with missing mass/redshift interpretations/ galaxy rotation rates/etc. boils down to our extremely poor understanding of gravity?

 

Best wishes;

[Qfwfq]

In other words, even if two bodies, e.g., the moon and the earth, were to stop in there tracks, they would never collide with one another. Each remains in its gravitational well (I should elaborate, but no time now).

:)

 

It really depends on what you mean by that 'if they were to stop in there tracks'. If they were place at the current distance but with no angular momentum, the would start to come toward each other and crash.

[Qfwfq]

Cosmologists calculate that there must be vastly more matter out there than we can physically observe. Many stars near the center of many galaxies have much higher velocities than they should have indicating a gravitational force we cannot see. Is it possible that the center of every galaxy contains a massive black hole and that these enormous masses are responsible for the vast quantity of matter that is unaccounted for? Are these billions of black holes a sizeable portion of the dark matter we are looking for?

Black holes are indirectly observable by x-ray emission and by behaviour of objects around them. I think it's largely a matter of how precisely astrophysicists can estimate the mass of galaxies.

 

However I don't think they would quite count black holes under the heading of dark matter. If you suppose you have measured the mass of a galaxy well enough, this means including the mass of any black holes or whatever internal stuff. I've known of astronomers reading Doppler shifts of stars in far galaxies at various radii and calculating stellar motions according to the overall distribution of mass, which implies that overall mass can be inferred reasonably well if you can get these calculations to match up.

 

I think the trouble is that there seems not to be enough mass in galaxies. If you propose black holes between galaxies, that's a different matter. I think that a non-uniform mass distribution that was sufficient for the purpose would have noticeable effects though, I think they've been looking for something finer, not yet observed.

[coldcreation]

Perhaps I used the wrong title for this thread. I was not suggesting anything that would support the theorized quantity of dark matter. What I was thinking is that maybe there's a whole lot more black holes out there than we think and maybe that's why it seems there must be all this alleged dark matter to make the current model work. When we look at things like the Hubble Deep Field the observation really tells us nothing about the quantity of supermassive objects that may lie at the edge of our depth of view. Just how massive could the oldest blackholes be and how many of them could there be. Could these numbers be high enough that current estimates of the quantity of dark matter are significantly off?

 

Applying Newton’s law of motion, Kepler’s third law planetary motion and the viral theorem (which asserts that for gravitating systems in statistical equilibrium, the gravitational potential energy must be twice the kinetic energy of the galaxies), it is shown that the mass of, say, the Coma cluster exceeds the mass attributable to the visible parts of the galaxies by a factor of twenty or more—implying that most of the mass in the cluster is in the form of dark matter.

 

Moving to even larger scales, the magnitude of the problem is even more precipitous within the largest agglomerations of matter known in the universe: superclusters. [The largest known structures in the universes are holes of empty space. The scale corresponding to these regions where the galaxy count is significantly low is about 30 to 50 times the scale of a cluster of galaxies].

 

Calculations have divulged that huge amounts of gravitating matter must be missing if the theory that outward centrifugal force is responsible for the balancing act with the inward attraction of gravity. Here, clearly stated, is the core principle the modern stance: it is separated totally from any direct dependence on the stimulus of nature—the discrepancy between gravity and velocity yield baffling forms of missing dark matter.

 

Gravity along with missing mass and centrifugal force are set up as three distinct polarities. Newtonian mechanics seems to work well when applied to the solar system. But going up the scale of masses to galaxies, to clusters of galaxies, superclusters and ultimately the mass density of the universe as a whole, the less compelling and the more uncompromisingly large the deviation from reasonable interpretation.

 

How can this be if local physics is global physics? There are three answers to this question, only one of which must be correct...

 

Coldcreation

[CraigD]

I’m intentionally restricting my comments to galaxy-scale phenomena, which I believe C1ay had in mind for this thread. Dark matter and larger scale phenomena are a big and fascinating subject, but, I think, off-topic for this thread.

… What I was thinking is that maybe there's a whole lot more black holes out there than we think and maybe that's why it seems there must be all this alleged dark matter to make the current model work. …

I think that, if there were a lot more black holes within the galactic bulge or disk, we’d observe at least these peculiar effects:

1. Lots of small, bright x-ray sources, from these black holes hot accretion disks where they exist near a lot of matter;
   
2. Star spectra with missing absorption lines, due to very matter-free regions where older black holes have swept space clear of the usual interstellar matter;
   
3. Multiple images of stars and Einstein rings within the galaxy, due to gravitational lensing by the black holes, vs. that by the weaker gravitational fields of other dark matter candidates, such as brown dwarfs or more exotic stuff.
   

I don’t believe we’re seeing enough of these to account for the large amount of dark matter needed withing a galaxy to explain presently observed galactic rotation (roughly ten time the amount of visible matter).

 

The MACHOs lying outside the visible galaxy proposed by the scientific mainstream to explain galactic rotation could consist of black holes, but this raises the problem of how such very dense objects could form. Still, I wouldn’t be surprised if MACHOs turn out to be black holes that formed by a very different process than the small stellar collapse and the large galactic core kind.

 

:hammer: A thought I had in responding to this thread is the possibility that the missing galactic matter could be accounted for if the galactic core black hole was many times more massive than currently believed. A quick, simplified calculation of average orbital velocities for this scenario quickly showed that this explanation predicts a rotation curve (the graph of average orbital velocity vs. distance from galactic center) even more in disagreement with observation than one that has neither black holes nor MACHOs. :smart:

Just how massive could the oldest blackholes be and how many of them could there be. Could these numbers be high enough that current estimates of the quantity of dark matter are significantly off?

Since young galaxies are full or large, short-lived stars, I expect that there are old star-sized black holes nearly as old as the galaxies – that is, in the 10-13 billion year range. Since they represent only part of the mass of the stars that formed them, I can’t see how they could begin to approach the mass necessary to account for dark matter.

 

In summary, I’m unable to make sense of any explanations for the galaxy rotation problem other than the conventional ones:

• MACHOs;
  
• Massive Non-compact halo matter (MANCHOs?);
  
• Weird, non-baryonic halo matter;
  
• Something wrong with our understanding of gravity (eg: MOND theory)
  

:) PS/griping: I wasn’t able to easily find much useful, numeric data that a hobbyist could use for galaxy simulations. If any of ya’ll are such hobbyists, and personally possess or know of such sources, I’d be grateful if you’d share ‘em.

[C1ay]

However I don't think they would quite count black holes under the heading of dark matter.

And that wasn't my intent here either. Although black holes are inherently dark I refer to dark matter as that non-emmisive matter like planets and asteroids and such.

[C1ay]

I think the trouble is that there seems not to be enough mass in galaxies. If you propose black holes between galaxies, that's a different matter. I think that a non-uniform mass distribution that was sufficient for the purpose would have noticeable effects though, I think they've been looking for something finer, not yet observed.

Black holes between galaxies is a possibility and we should be able to detect them if there is a source of light behind them such that we can see it's deflection. I also wonder though about the deep field holes for which there is no source of light behind them for us to use to detect them.