Imagine a soap bubble that weighs more than 80 percent the mass of an entire galaxy and is about 200,000 light years in diameter. In order for it to remain a bubble, like any bubble, it must be perfectly smooth, perfectly round, essentially absolutely perfect. Any deviation from this homogeneous symmetry and it would pop like any soap bubble, except for dark matter it would end up falling inward like a collapsed star. Following the world lines which define the center of mass for the entire system it would carry stars and dust and everything we see and crunch it down into a gravitar the likes of which we have never observed.
First of all, I refer to black holes as gravitars. Not only is this an accurate description of the final possible phase of a star or any matter crushed into a small enough space, it’s easier to write than black hole, or super massive black holes, when ultra gravitar is equally descriptive and simply more efficient.
Dark matter halos are a problem for science. These are the theoretical pockets of dark matter into which the first baryonic matter falls to form the first stars and eventually the galaxies themselves. The idea that as they fly through the universe maintaining perfect symmetry and not encountering other dark matter pockets which would destabilize the halo and cause it to collapse are not just counterintuitive, they are a little ridiculous.
We can say the radiant pressure of all the matter and energy expulsion of a galaxy work to push out against the halo and inflate the bubble but that is weak tea given the proportions we are talking about. The galaxy and all the energy it could produce in its lifetime are but a fraction of a fraction of the amount of gravitational potential locked in the halo. If that thing came down all the stars in the universe couldn’t stop it. Which leads to the next question, why have we observed no evidence of halo collapse.
The most famous inconsistency is known as the satellite problem. Simply stated if halos are what hold galaxies together they should be much, much heavier than they look. In fact most of the weight would be invisible and can only be infered by measuring the weight of visible matter. This means galaxies should attract a large number of dwarf satellite galaxies, and I mean a very large number. Yet as we look across the visible universe only the bullet cluster seems to have these kinds of proportions. It’s an outlier, not statically representative of the observable universe as a whole. Galaxies to not appear to be as heavy as the halo model needs them to be.
Yet for me, the strongest evidence for the halo problem, and the strongest evidence against it, is the correlation problem. Every galaxy has a central ultra gravitar, in our own galaxy it’s called Sagittarius A-star, and it’s about 4 million solar masses, fairly small as these things go.
When we measure the size of these central gravitars, then compare this to the radial velocities of the stars in the galaxy a strict correlation emerges. The bigger the gravitar, the faster the stars orbit, the smaller the gravitar, the slower the stars move. This is objective observation, and it creates a massive problem for halo theory.
Think about it. This implies that the central gravitar is directly linked to the radial movement of the galaxy, that the process which formed it also set in motion the formation of the galaxy itself. More than that it means there is a relationship between that gravitar and stars which formed billions of years after it collapsed so far from it there should be no relationship at all. Yet while there is clear evidence of some kind of relationship, there is no observed evidence of a relationship with the halo because by definition it is something which cannot be observed, even though that is what is supposed to be driving the velocity and holding the entire galaxy together.
The correlation problem means there is more physical evidence for a relationship between gravitars and their host galaxies than there is between galaxies and dark matter, whose evidence rests solely in theory and complex computer models and cannot be observed.
The correlation should be with the stars and the size of the halo, not between the stars and the ultra gravitar. Of course this correlation doesn’t disprove dark matter or halo theory, but it does mean halos have more than a few problems, and dark matter itself has some serious explaining to do…