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From neutron star to black hole?





Hazim
I had read before about the stellar evolution. They showed that the neutron star at certain conditions explodes (i.e the supernova) and then a black hole will be founded. From my modest information, the neutron star is made of broken material(atom) and its density is almost the same as the neutron itself Question . If the supernova is the explosion of this star, then the star will be dispersed in the space. If this is true, then how come the black hole is made of matter, most dense matter..?

Regards,
Hazim
Bikerman
Hazim wrote:
I had read before about the stellar evolution. They showed that the neutron star at certain conditions explodes (i.e the supernova) and then a black hole will be founded. From my modest information, the neutron star is made of broken material(atom) and its density is almost the same as the neutron itself Question . If the supernova is the explosion of this star, then the star will be dispersed in the space. If this is true, then how come the black hole is made of matter, most dense matter..?

Regards,
Hazim

This is all wrong.
A neutron star cannot possibly explode and cannot become a black-hole. A neutron star is the remnants of a 'normal' star which doesn't quite have enough mass to become a black hole. It shrinks down, after the supernova of the normal star, until all the matter is as compact as it possibly can be (ie no electrons, just neutrons packed tightly together). If the original star were a bit larger then it wouldn't stop at this point - it would carry on shrinking into a black hole.
Hazim
Bikerman wrote:
This is all wrong.
It shrinks down, after the supernova of the normal star

How it shrinks down if the supernova disperses the matter of the original star?
Bikerman
It doesn't. Only a tiny fraction is actually ejected into space. The rest is gravitationally bound and collapses quickly back down.
As long as the star is burning the heat/energy generation exerts an outward force on the star which stops it from collapsing. When this ends (after the hydrogen runs out it begins to fuse helium, which produces much more heat causing the sun to expand, but is ultimately the last stop before fusion cannot continue - at which point nothing is 'pushing' the star out, so it collapses back into itself. If it is sufficiently massive, the collapse is so strong that even matter cannot stop it, so the actual atoms collapse into themselves leaving what we call a singularity - a point in space of essentially infinite gravity where all the laws of physics are completely out to lunch.
Hazim
Thank you. I now understood how the black hole is formed.. What about the time duration of the supernova stage?
Bikerman
Depends when you measure from. From the time it starts fusing helium it could be millenia. From the time fusion stops - seconds.
Wiki has a reasonable article, but if you want more then I can direct you to some of my colleagues in another forum who can answer questions in great detail.
http://en.wikipedia.org/wiki/Supernova
Hazim
Thanks. I'll see the article on wikipedia later. No, I don't want more details.... Thank you Bikerman.

Regards,
Hazim
_AVG_
Correct me if I'm wrong (I was never good at Stellar Evolution), but doesn't a Red Super Giant undergo a Supernova to leave a Neutron Star and only under certain conditions (i.e. the Volkhoff limit or something) will the Neutron Star collapse into a Black Hole?
Bikerman
pretty much. The Red Giant part is only a description applied to a 'normal' main sequence star that has used up the hydrogen in the core.
_AVG_
Bikerman wrote:
pretty much. The Red Giant part is only a description applied to a 'normal' main sequence star that has used up the hydrogen in the core.


So then, do all stars undergo Supernovae or only main sequence stars?
In other words, what are the conditions necessary for a star to undergo a supernova?
Then again, what exactly are the conditions for a star to become or main sequence star and/or to leave the main sequence?

Forgive me. I'm quite confused.
Bikerman
Most stars go Nova not supernova.
Main sequence refers to the stars position on the HR diagram:

Most stars go through similar stages as they age, but the more massive a star, the quicker it ages, so very massive stars are only main sequence for a short time before going supernova and perhaps becoming a black-hole. The sun is fairly typical.

More information Here
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