Q&A: Supernova Remnants and Neutron Stars

Q:
1a. "However, such massive stars are observed to be quite rare at present. Whether they were more abundant in an earlier era billions of years ago when galaxies were forming is still an open question, though it is considered highly unlikely that there would be enough of these objects to explain the dark matter. "

1b. Since these huge stars are prone to collapse, wouldn't it seem to perfectly plausible that a good majority of these stars have already collapsed. Especially ones that are multiple times bigger than ones we know of. They would have collapsed millions and millions...etc, years ago, so of course we don't see them now. The bigger, the less stable, right? So all the biggest stars should of already collapsed.

2a. "First, research over the past few years has shown that the mass of the supermassive black holes at the centers of galaxies is less than a percent of the mass of their host galaxy."

2b. What research yielded this evidence or idea. How is it possible to measure the density of a black hole, let a lone a supermassive black hole. Remember, black holes may be portals, or doors, or anything. If everything is being "sucked" into a black hole, the majority of the mass would be at the end of this black hole... and if there aren't any differences in mass from the front to the rear of the black hole, common sense would say, its obviously going somewhere else. ?

A:
1. Certainly very massive stars in the early universe would have already exploded and collapsed to leave behind neutron stars and black holes. In the case where neutron stars were produced, the amount of material expelled would have been greater than the amount left behind in the neutron star, and much of the expelled matter is in the form of elements such as oxygen, etc. For these reasons, it is difficult to account for dark matter, which is more abundant that normal matter, with explosions that produce neutron stars. The same problems exist for explosions that produce black holes.

This leaves only stars that collapse directly to form black holes without an explosion. It is possible that almost all the stars formed in the first generation were of this type, but it is considered highly unlikely.

Furthermore, it does not get around the problem that the amount of normal matter deduced to exist (from the observed ratio of deuterium nuclei to normal hydrogen nuclei) in the first few minutes of the Big Bang is insufficient to explain the amount of dark matter plus normal matter observed today.

2. The research involves looking at the motions of stars in the centers of galaxies. These motions imply a dark, massive body whose mass can be computed from the speeds of the stars. The matter that falls into a black hole adds to the mass of the black hole. Its gravity doesn't disappear from the universe? .