Is a pulsar denser than a neutron star?

Answer 1

The very definition of a black hole is a stellar body dense enough to have an escape velocity greater than that of light -- in other words, light that comes close enough to its event horizon will be trapped around it forever. If a star dies and it has enough mass to be compressed to a high-enough mass-to-radius-squared ratio to have such a high escape velocity, then a black hole will result. Otherwise, it will become a neutron star -- extremely dense, to be sure, but not dense enough to trap light, and therefore not as dense as a black hole.

Answer 2

Generally a white dwarf is the largest out of these three, measuring several thousand miles across. A neutron star would be about 15 miles across. The size of a black hole is harder to define. The actual mass is contained in a point of zero volume called a singularity, so the size is usually measure by the event horizon which would be in the range of about 10 to 100 miles across for most black holes. Supermassive black holes are a different matter and may have event horizons millions to billions of miles across.

Answer 3

While these three are similar in that they can all be stellar remnants, there are significant differences. Generally speaking, each can represent a stage or the end result in the collapse of a star, and in certain circumstances it's actually possible for a white dwarf to increase in mass as it acquires additional matter and collapse further and then become a neutron star, or a neutron star to further collapse to a black hole as mass is added to it. The density increases respectively in this sequence, and the size decreases; a normal star is very large by comparison to a white dwarf; a white dwarf is very large by comparison to a neutron star. (A neutron star would be only slightly larger than the event horizon of a black hole of similar mass). The white dwarf is luminous; a neutron star would only be marginally luminous depending on its temperature (and even then mostly in non-visible wavelengths)... and black holes are not luminous (except for extrinsic sources caused by infalling matter and possibly quantum effects). Another dissimilarity is that different outward "balancing" forces are in effect for each. These are degeneracy pressures, the name given to the forces which

prevent further gravitational collapse which apply to a white dwarf and neutron star. White dwarfs resist further collapse against the pull of gravity because of electron degeneracy pressure - a simplified view of this being that the atoms can't get any closer together, up to a certain mass limit called the Chandrasekhar limit, roughly 1.4 times the mass of the sun for common stars. Beyond this limit the white dwarf would likely collapse into a neutron star. Neutron stars resist collapse because of neutron degeneracy pressure - which also has an upper mass limit (the TOV limit) above which acquisition of additional mass may cause them to collapse further into a more dense object such as a black hole. Because white dwarfs and neutron stars have escape velocities less than c (the speed of light) it is possible for them to be observed directly through electromagnetic radiation; in the case of a neutron star, these can emit beams of radio energy observable from earth using radio telescopes. Because these seem to pulse at fixed periods (attributed to their rotation) they are called pulsars. The density of matter in a white dwarf and neutron star can be calculated with some accuracy and is finite; the type of matter can be described by our current physical theories. By contrast, the density of matter at the center of a black hole differs in that it is considered infinite (i.e., the matter is concentrated at a point called a singularity, occupying zero volume) and the type of matter is not described adequately by our physics. Again, this matter can't be observed directly because the escape velocity inside a black hole (within the event horizon) exceeds 'c'. Black hole theory also predicts other significant effects consequent to predictions of general relativity not evidenced with either a white dwarf or neutron star which make black holes rather unique.

Answer 4

There are several key differences between these three entities, a white dwarf, neutron star, and black hole. Generally speaking, each can represent a stage in the collapse of a star, and in certain circumstances it's actually possible for a white dwarf to increase in mass as it acquires additional matter and collapse further and become a neutron star, or a neutron star to further collapse to a black hole as mass is added to it. The density increases respectively in this sequence, and the size decreases; a normal star is very large by comparison to a white dwarf; a white dwarf is very large by comparison to a neutron star. (A neutron star would be only slightly larger than the event horizon of a black hole of similar mass). The white dwarf is luminous; a neutron star would only be marginally luminous depending on its temperature (and even then mostly in non-visible wavelengths)... and black holes are not luminous (except for extrinsic sources caused by infalling matter and possibly quantum effects). Different outward "balancing" forces - or degeneracy pressures, the name given to the forces which prevent further gravitational collapse, prevail in a white dwarf and neutron star; white dwarfs resist further collapse against the pull of gravity because of electron degeneracy pressure - a simplified view of this being that the atoms can't get any closer together, up to a certain mass limit called the Chandrasekhar limit, roughly 1.4 times the mass of the sun for common stars. Beyond this limit the white dwarf may collapse into a neutron star. Neutron stars resist collapse because of neutron degeneracy pressure - which also has an upper mass limit (the TOV limit) above which acquisition of additional mass may cause them to collapse further into a more dense object such as a black hole. Because white dwarfs and neutron stars have escape velocities less than c (the speed of light) it is possible for them to be observed directly through electromagnetic radiation; in the case of a neutron star, these can emit beams of radio energy observable from earth using radio telescopes. Because these seem to pulse at fixed periods (attributed to their rotation) they are called pulsars. The density of matter in a white dwarf and neutron star can be calculated with some accuracy and is finite; the type of matter can be described by our current physical theories. By contrast, the density of matter at the center of a black hole differs in that it is considered infinite (i.e., the matter is concentrated at a point called a singularity, occupying zero volume) and the type of matter is not described adequately by our physics. Further, this mass can't be observed directly because the escape velocity inside a black hole (within the event horizon) exceeds 'c'. Black hole theory also predicts other significant effects consequent to predictions of general relativity not evidenced with either a white dwarf or neutron star which make black holes rather unique.

Answer 5

A pulsar and a neutron star are the same thing.

See related question.

Answer 6

A neutron star