Why are we so sure that Black holes only constitute a relatively small part of the mass in our Universe?

Question

In a preceding question I asked if the mass missing from our Universe ("Dark matter") could be explained by the mass that is hidden in Black holes. Two relevant answers to my question stated that the mass present in Black holes is far too small to account for the missing matter. My question now is how do we know that the quantity of matter hidden in Black holes is relatively small. The early Universe formed a first generation of stars on average enormously heavy (up to 100 times the mass of our sun). Many of them may have clustered and then collapsed into enormous Black holes. If such Black holes would exist alone in empty space, having absorbed all matter around them, the only radiation coming from them would be Hawkins radiation, which I think would be impossible to detect on astronomical distances. Such giga Black holes would also show a very anomalous gravity pattern, but again if the Black hole is a loner in empty space, this pecular gravity field could not be observed by us.

Answer 1

We do have a fairly accurate idea of the age of the universe, and from this it can be determined that such super black holes have not had time to form. You make a good point that black holes themselves give off little energy, but matter falling into a black hole gives off an immense amount of high energy radiation. Also, while a black hole could exist in an area with no other matter, it would still act as an immense 'gravity lens', affecting the appearance of objects behind it. Several automated astronomical search programs are designed just for this type of observation and have not discovered the number of black holes you suggest. Great questions, BTW.

Answer 2

Actually.. Dark matter is NOT the missing mass of the universe
Dark matter is defined as the undetected matter in the universe which is not luminous. We know of its existence because of how clusters of stars and galaxies rotate...

Coming to MISSING MASS OF UNIVERSE....
actually black holes have just some millions times of mass of sun. which is very less .. so black holes do not constitute the missing mass of universe
scientists believe that almost 90% of missing mass is present in
universe
In their efforts to find the missing 90% of the universe, particle physicists theorize the existence of tiny non-baryonic particles that are different from what we call "ordinary" matter. Smaller than atoms, Weakly Interactive Massive Particles are thought to have mass, but usually interact with baryonic matter gravitationally--they pass right through ordinary matter. Since each WIMP has only a small amount of mass, there needs to be a large number of them to make up the bulk of the missing matter. That means that millions of WIMPs are passing through ordinary matter--the Earth and you and me--every few seconds. Although some people claim that WIMPs were proposed only because they provide a "quick fix" to the missing matter problem, most physicists believe that WIMPs do exist ...
But the research is still in progress.. NO results are available

Answer 3

I think black holes have been considered as a possibility. But how could massive black holes explain the strange galactic rotation curves that are being observed? A better explanation would have to involve many smaller black holes distributes all around the galaxy.

Answer 4

I don't see how such a massive black hole could be a loner in empty space. For a black hole to grow very heavy, it needs to be in a region with lots of material.