Yes. They have a density of infinity
Neutron stars contain some of the densest material in the universe, with a mass comparable to the sun packed into a sphere roughly the size of a city. The extreme density is due to the collapsing core of a massive star after a supernova explosion.
Our mathematical understanding of physics "breaks down" at the singularity of the black hole; in a very real sense, we CANNOT KNOW what happens in there. Check back in about 50 years; we may have a better understanding of physics by then. But until then, I think the answer would be "Probably."
In theory it is compressed down into a singularity. This is why black holes are the densest objects in the universe. All that mass is being squeezed down into a single point in space.
The densest thing in the universe is a neutron star, which is formed when a massive star collapses in a supernova explosion. Neutron stars are incredibly dense, with a mass greater than that of the Sun packed into a sphere only about 12 miles in diameter. Their density is so extreme that a teaspoon of neutron star material would weigh billions of tons on Earth. In comparison, neutron stars are much denser than other celestial objects like white dwarfs and even black holes.
red orange black
Probably the supermassive black holes that are believed to be at the centers of many (perhaps most) large galaxies. These may be related to quasars.
Would be the same as asking, "What is the densest stuff in the universe?" As far as I know, the stuff that theoretically makes up black holes is quite probably the densest stuff in the universe. As far as elements, Osmium (atomic number 76) is the densest with a specific gravity of 22.587 +/- 0.009 g/cm^3 according to Wikipedia.A2. and neutronium lies in between the above two.
No
No, dark matter is quite a different kind of thing. A dark hole may have absorbed some dark matter, but pressumably that would become indistinguishable from the normal matter, once it gets crushed by the enormous gravity of the black hole.
It is not old enough. It is estimated that it would take trillions of years for a white dwarf to a black dwarf. The universe is only about 13.8 billion years old.
The electicity would create a black hole and destroy the universe
The densest stars are neutron stars, which are formed from the collapsed core of a massive star after a supernova explosion. Neutron stars are incredibly dense, with a mass greater than that of the Sun but compressed into a sphere only about 10 kilometers in diameter. The density of neutron stars is so high that a sugar-cube-sized amount of neutron star material would weigh as much as Mount Everest.