"neutron" star etc.

[donmila]

I have once heard, many years ago, of stars, when they lose their fuel, or sometning, that they form into something callled a "neutron star". . .
just what is it, and what is the relationship, if any, to a "black hole"?

On the subject of black holes: Is it possible for the objec in question to gather enough material from the surrounding stars which the seem to cannibalize, to eventually become a light emitting sun again, and, repeat the process (for lack of a better anology, birth, light giving sun, super giant phase, collapse into a "black hole" ad infinitum....?
PS...I have a limited understanding of astronomical terms, so, try to keep it within the non technical language, if possible. Thanks. Donmila.

[Orstio]

This link should help you:

http://www.eclipse.net/~cmmiller/BH/blkmain.html

On the subject of black holes: Is it possible for the objec in question to gather enough material from the surrounding stars which the seem to cannibalize, to eventually become a light emitting sun again, and, repeat the process (for lack of a better anology, birth, light giving sun, super giant phase, collapse into a "black hole" ad infinitum....?

Actually, that's a bit backwards, but understandably.  As a black hole gains mass, it becomes a larger and more powerful black hole.

There is a theory that a black hole starved of matter to absorb would continue to give off high-energy emissions called Hawking radiation, and eventually lose mass due to this.  As it loses mass, the extreme gravity-well around it would dissipate, and eventually the space would return to a near-normal curve again.

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/010703a.html

[Retrospector]

There is a lot to be said about this subject, but here are a few comments. I don't pretend to be an astrophysicist myself!

This site has some numbers. A neutron star is thought to be in general the remnant of the core of a massive star whose atoms have collapsed into a packed mass of neutrons, likely following a supernova explosion. But there is an upper limit on the mass that can go into a neutron star.

http://hyperphysics.phy-astr.gsu.edu/hbase/astro/pulsar.html

For a sufficiently massive star, an iron core is formed and still the gravitational collapse has enough energy to heat it up to a high enough temperature to either fuse or fission iron. Either in the aftermath of a supernova or in just a collapsing massive star, the energy gets high enough to break down the iron into alpha particles and other smaller units, and still the pressure continues to build. When it reaches the threshold of energy necessary to force the combining of electrons and protons to form neutrons, the electron degeneracy limit has been passed and the collapse continues until it is stopped by neutron degeneracy. At this point it appears that the collapse will stop for stars with mass less than two or three solar masses, and the resulting collection of neutrons is called a neutron star. The periodic emitters called pulsars are thought to be neutron stars.

If the mass exceeds about three solar masses, then even neutron degeneracy will not stop the collapse, and the core shrinks toward the black hole condition.

The collapsing mass shrinks below the Schwarzshild radius, after which (in the General Relativity picture) light cannot escape from it.

[alokmohan]

Neutron stars ar dead bodies of large stars if after they throw away the supenova and even then manages to have more than 1.4 times the mass of sun ,called chanrashekar limit.If it ismore than three suns after becominga netron star the poor chap is condemnedto be black hole.

[remcook]

XMM Newton finds a spot on a neutron star:

http://www.esa.int/esaSC/Pr_15_2004_s_en.html

[alokmohan]

What  UNRDESTAND IS BOTH xRAYS AND GAMMA RAYS ARE EMITTED.Whats special I fail to understand.

[Astronuc]

X-rays and gamma rays are both electromagnetic radiation, i.e. photons.  X-rays tend to be of lower energy.

X-rays are formed by the emission of photons when electrons fall back into orbit about an atom and reflect the characteristic energies of the elements atoms.

Gamma rays are formed from nuclear reactions (such as decay of an excited nucleus) and reactions invovling subatomic particles.

[alokmohan]

Can you say if there is anything special in Geminga in the sense of known astronomical object of past?Or it is new discovery?