How do astronomers know a black hole is not a neutron star?

Question

details please

Answer 1

The gravity and they aren’t black, or invisible.

Black holes have more gravity and the effects are greater.
Also black holes don't emit the same radiation as Neutron Stars do. Neutron Stars are not invisible.

According to Wikipedia: http://en.wikipedia.org/wiki/Neutron_Star
"In 1967, Jocelyn Bell and Antony Hewish discovered regular radio pulses from the location of the Hewish and Okoye radio source. This pulsar, was later interpreted as originating from an isolated, rotating neutron star. The energy source of the pulsar is the rotational energy of the neutron star. The largest number of known neutron stars are of this type (See Rotation-powered pulsar).

In 1971, Riccardo Giacconi, Herbert Gursky, Ed Kellogg, R. Levinson, E. Schreier, and H. Tananbaum discovered 4.8 second pulsations in an X-ray source in the constellation Centaurus, Cen X-3. They interpreted this as resulting from a rotating hot neutron star. The energy source is gravitational and results from a rain of gas falling onto the surface of the neutron star from a companion star or the interstellar medium (See Accretion-powered pulsar).

In 1974, Antony Hewish was awarded the Nobel Prize in Physics "for his decisive role in the discovery of pulsars" without Samuel Okoye and Jocelyn Bell who shared in the discovery."

Neutron Stars also have a magnetic field a hugely strong one, and that creates electrical effects in matter that is near the star. Black holes are pure gravity with no magnetic field.

From the same source:
"Neutron stars may "pulse" due to particle acceleration near the magnetic poles, which are not aligned with the rotation axis of the star. Through mechanisms not yet entirely understood, these particles produce coherent beams of radio emission. External viewers see these beams as pulses of radiation whenever the magnetic pole sweeps past the line of sight. The pulses come at the same rate as the rotation of the neutron star, and thus, appear periodic. Neutron stars which emit such pulses are called pulsars.

The most rapidly rotating neutron star currently known, PSR J1748-2446ad, rotates at 716 revolutions per second. A recent paper reported the detection of an X-ray burst oscillation (an indirect measure of spin) at 1122 Hz from the neutron star XTE J1739-285. However, at present this signal has only been seen once, and should be regarded as tentative until confirmed in another burst from this star."

Finally we see stars go nova and supernova frequently, we especially look for them. When that happens we know the size of the star and if it is less than 20 times the mass of our sun, but bigger than our sun it can form a neutron star, but it is too small to form a back hole.

From the same source:
"A neutron star is formed from the collapsed remnant of a massive star, a Type II, Type Ib, or Type Ic supernova and models predict that it consists mostly of neutrons. It is a cold star supported by the Pauli exclusion principle repulsion between neutrons. A neutron star is one of the few possible conclusions of stellar evolution.

A typical neutron star has a mass between 1.35 and about 2.1 solar masses, with a corresponding radius between 20 and 10 km — 30,000 to 70,000 times smaller than the Sun. Thus, neutron stars have densities of 8×1013 to 2×1015 g/cm³, about the density of an atomic nucleus.

In general, compact stars of less than 1.44 solar masses, the Chandrasekhar limit, are white dwarfs; above 2 to 3 solar masses (the Tolman-Oppenheimer-Volkoff limit), a Quark star might be created, however this is uncertain. Gravitational collapse will always occur on any star over 5 solar masses, inevitably producing a black hole."

Black holes do emit radiation; hawking radiation which we can't detect and at the poles Gamma Ray bursts which comes from the matter being violently broken apart before it has a chance to hit the event horizon of a black hole.

Answer 2

If a black hole could exist it would be the result of a collapsed neutron star.
A 2 solar mass neutron star 20 km in diameter would be virtually invisible.
At 50 million miles it would be so small that it could only be detected by it's influence on it's surroundings,and neutron stars do exist.
A black hole would be a 2 solar mass entity 3km in diameter whose surface gravity would be such that the escape velocity would be greater than the speed of light.
A black hole is a generally accepted entity by astronomers.
However there are a number of very valid reasons why a black hole in a non viable entity.

Answer 3

A black hole does not have a surface the way a neutron star (or any other star) does.
When matter falls onto a black hole, it disappears into the event horizon. It does not emit radiation (the accretion disk around a black hole will emit xrays and gamma rays as friction heats the material, but once the matter passes the event horizon there is no emission).
When matter falls onto a neutron star, the matter will fuse and release intense xrays and other radiation (including visible light, radio waves, microwaves, etc).

So if they analyse the radiation of an object and any energy comes from an accretion disk around the object but not from the object itself, its a black hole.

Answer 4

the only similarities with a neutron vast call and a black hollow is that each is rather huge. A neutron vast call rotates at a severe speed and it has a useful magnetic container from which severe potential streams of electrons are ejected, this type of vast call is normally pronounced as a pulsar. this is regularly of small radius. No mild of any type can get away from a black hollow. I, for one, supply no credence to Hawking radiation, it defies the very description of a black hollow.

Answer 5

usually a quazar