What is bigger a black hole or a neutron star?

Answer 1

It all relates to what you define as big.

A black hole is an infinite region in space with an infinite density. It's "event horizon" is not infinite.

If you wish to categorise between size of a neutron star and a black hole's "event horizon", then a black hole is, in most cases larger - but there are micro black holes, which exhibit all the characteristics of a black hole but have a much smaller "event horizon".

In the physical sense, everything is bigger than a black hole, but in a terminological sense (the event horizon) it would depend on the mass of the black hole.

Answer 2

A significant difference between a neutron star and a black hole is that the neutron star has not fully collapsed. A notional "outward" force, neutron degeneracy pressure, can hold the shape of the neutron star against the inward pull of gravity and thus prevent the neutron star collapsing to a black hole. If the mass was to increase beyond a certain maximum (formally called the Tolman-Oppenheimer-Volkoff limit), for example, by additional infalling matter, then the neutron star could collapse further and possibly become a black hole.

Hence the escape velocity from a neutron star does not equal or exceed c, the speed of light; and electromagnetic energy can still escape from a neutron star, and so, unlike a black hole, it is directly observable. Spinning neutron stars emitting amounts of electromagnetic radiation measurable to radio telescopes are known as pulsars.

Another notional difference between the two is that our current physical theory does not fully describe black holes; the nature of the matter at the center of a black hole (the singularity) is not fully understood, known laws of physics seem to no longer apply. The singularity of a black hole is believed to be of zero volume and infinite density - by contrast, the matter in a neutron star, while highly dense, can still be fairly completely described by current physical theory.

Answer 3

Stars 8 to 10 times more massive than the sun or more will become neutron stars. Stars above 25 solar masses are likely to become black holes.