Question about exploding neutron stars

[gonzo]

I have a question about the time scale for a certain type occurrence causing a neturon star to explode, and a related question about the conditions of this occurrence.

If you have a binary star system with one of the stars being a neutron star, I read that if the other star sucks off enough mass from the neutron star then the NS won't have enough mass to hold itself together and will explode violently from internal pressure.

I'm interested first in what would be required in terms of orbits and relative masses for the other star to suck off mass from the neutron star instead of the other way around (thus forming, eventually, a black hole in the opposite process).

And also over what kind of time scale this might occur. By time scale I mean assume you had a sattelite probe in the system watching both stars and collecting data. What is the time evolution of the process starting with when the probe stats to notice matter flowing from the neutron star to the partner star?

As a side question, will this flow of mass give off extra energy? I assume the gas will be super heated and so give off high energy photons (Xray and higher, like the neutron star itself?), or will it glow more in the visible?

Given how fast a neutron star is likely to be rotating, how would this even "look"? Would the mass spiral out from the star in ever larger turns until it reached the partners star sucking it up?

Thanks.

 

[mathman]

If you have a binary star system with one of the stars being a neutron star, I read that if the other star sucks off enough mass from the neutron star then the NS won't have enough mass to hold itself together and will explode violently from internal pressure.

I believe you misread the description. The neutron star is sucking mass from its companion (usually a red giant). At some point it reaches a certain critical mass and goes supernova. This is the scenario to produce Type Ia supernova, which is an extremely bright standard candle. Studying these SN's has led to the conclusion the expansion of the universe is accelerating.

 

[gonzo]

In the GR book I read it says that if a neutron star loses mass (the only way it mentions this can happen is to a binary partner) then it can pass the critical threshhol where the pressure is greater than the gravity and it becomes unstable and explodes.

It also says that if it is the neutron star that sucks mass from the binary partner, than it will eventually pass the threshold in the other direction and become a black hole.

It also says the neutron stars are the result of a supernova ... they are what's left after a star explodes (or "bounces" off the neutron star core that forms).

 

[Labguy]

This is the scenario to produce Type Ia supernova, which is an extremely bright standard candle.

Actually, a Type Ia supernova only comes when a White Dwarf, not a neutron star, accretes matter from a companion. There are some more specifics required such as the exact carcon/oxygen composition of the WD, etc. but even in accreting white dwarf stars this (Type Ia) is very rare.

In the GR book I read it says that if a neutron star loses mass (the only way it mentions this can happen is to a binary partner) then it can pass the critical threshhol where the pressure is greater than the gravity and it becomes unstable and explodes.

I have read a lot of books and papers on stellar evolution and have never heard of neutron stars losing mass to any companion star. At that huge density and surface gravity I can't think of any type of companion star that could pull mass off of a neutron star other than another neutron star or black hole, where it is possible according to one theory. But, since the surface of a neutron star is a shell of (usually) iron of extreme density, with a neutron "superfluid" inside there is no atmosphere to be lost to even a dense companion.

It also says that if it is the neutron star that sucks mass from the binary partner, than it will eventually pass the threshold in the other direction and become a black hole.

It also says the neutron stars are the result of a supernova ... they are what's left after a star explodes (or "bounces" off the neutron star core that forms).

This part is exactly as described in most sources. If the neutron star passes ~3.2 solar masses by accreting matter it would collapse directly to a black hole.