Question about Neutron Stars

[Fallingstar1971]

If you had a binary system, say a neutron star and a supergiant, could the neutron star collect enough matter to nova or supernova like a white dwarf?

 

[neilsox]

Supernova, perhaps, but not like a white dwarf does it. as the starting conditions are very different. My guess is the neutron star would need to double or more it's mass in a very brief period to Supernova, so typical red giant stars don't have enough mass to trigger a supernova. Are you sure a white dwarf can produce a supernova other than at the instant of it first becoming a white dwarf? Can a neutron star collapse to a black hole without producing a bright flash of light and radiation?
I see no reason why a neutron star can't nova. My guess is a small percentage of the novas are nuetron stars rather than white dwarfs. Neil

 

[Fallingstar1971]

Yes white dwarfs can supernova or repeatedly nova if the circumstances are right. (Exceeding 1.44 solar masses)

If Im not mistaken, thats a type 1a

But I dont know about neutron stars, with all that pressure, the new matter could be reduced to neutrons making a bigger star, Im kinda wondering if there is an upper limit for these types of stars that could cause them to supernova or would it just collapse it into a black hole


Star

 

[ramparts]

That's a very good question. I'm pretty certain neutron stars exceeding their mass limit (they do have one) won't go supernova, as I've never heard of this sort of supernova in the literature, but I'm not sure why. Here's the most likely explanation I can think of: a Type Ia supernova is a result of the white dwarf being torn apart having exceeding its mass limit. When a neutron star exceeds its mass limit, you get a black hole, so clearly that's not going to be torn apart

 

[origin]

That's a very good question. I'm pretty certain neutron stars exceeding their mass limit (they do have one) won't go supernova, as I've never heard of this sort of supernova in the literature, but I'm not sure why. Here's the most likely explanation I can think of: a Type Ia supernova is a result of the white dwarf being torn apart having exceeding its mass limit. When a neutron star exceeds its mass limit, you get a black hole, so clearly that's not going to be torn apart

It is an interesting question - if the neutron star exceeded the limit and collapsed to a black hole I would assume there would be a shock wave just as a shock wave is produced in a star that goes super nova and blows off the outer layers of the star. But maybe there is not shock wave becasue there is no matter eject. A shock wave is not going to propegate through essentiall empty space.

As the neutron stars mass collapses to a black hole I would imagine that there would be a huge release of radiation as the 'neutrons' accelerated towards the core though.
:?

 

[kg]

If you had a binary system, say a neutron star and a supergiant, could the neutron star collect enough matter to nova or supernova like a white dwarf?

Yes it can! Much of the energy is emitted as x-rays and they are known a x-ray bursters. Here is a wiki page on them.
http://en.wikipedia.org/wiki/X-ray_burster

Here is a bit about nova which I've quoted.
http://en.wikipedia.org/wiki/Nova
"Astronomers theorize however that most, if not all, novae are recurrent, albeit on time scales ranging from 1,000 to 100,000 years.[4] The recurrence interval for a nova is less dependent on the white dwarf's accretion rate than on its mass; with their powerful gravity, massive white dwarfs require less accretion to fuel an outburst than lower-mass ones.[1] Consequently, the interval is shorter for high-mass white dwarfs.[1]"

So it seems that the surface gravity of a neutron star is SO strong that...
"The X-ray bursts emitted from most of these systems recur on timescales ranging from hours to days, although more extended recurrence times are exhibited in some systems...."

But I don't see anything here that says what happens when a neutron star accreats enought matter to colapse into a black hole.

 

[ramparts]

Hi kg,

This isn't quite the same thing - in particular, this happens as a phenomenon in general with neutron stars and black holes, not as a special event that happens when a neutron star exceeds its mass limit. Also, this is purely radiative. There's no "explosion" of matter, as there is in an actual supernova (for the reasons I discussed above - there isn't any matter to make a supernova!).

 

[kg]

Hi kg,

This isn't quite the same thing - in particular, this happens as a phenomenon in general with neutron stars and black holes, not as a special event that happens when a neutron star exceeds its mass limit. Also, this is purely radiative. There's no "explosion" of matter, as there is in an actual supernova (for the reasons I discussed above - there isn't any matter to make a supernova!).

Fallingstar1971 had asked if a neutron star could go nova or super nova like a white dwarf. I was refering to the similarity of novas to x-ray bursters in that they are both caused by a runaway fusion explosion on the surface of the white dwarf or neutron star.

 

[SpaceTas]

Good question. I am a bit stumped. There are a couple of theory people who might have an idea.
I'll try to get an answer but it might take a while.

Here's my best guess: (i've just deleted a lot about the white dwarf case, and type I burst on neutron stars)

So far only 1 or 2 neutron stars have measured masses a above 1.4 solar mass, but none as high as 3 solar masses. This suggests mechanisms that limit accretion and sure enough there are some.

To collapse the neutron star has to go from 1.4 solar mass to about 3 solar masses to collapse rather than go from 1.4 to just over 1.4 solar masses as is the case for many white dwarfs. So that's a lot of mass to accumulate. The case of a Cyg X-3 comes to mind. It has a neutron star deep inside the extended wind/atmosphere of a red giant. Here the accretion rate and total mass available would be enough. All other systems there are ways to shut off the accretion (tidal evolution of binary, the propeller effect).

I suspect what will happen when a neutron star goes over the limit (it is not as well defined as limit for white dwarfs) is that the too heavy neutron star will quietly just collapse into a black hole. There really isn't much size difference and surface gravity difference between a neutron star and a black hole. So the escape velocity in both cases will be so high that nothing on the neutron star can escape before/as it collapses. Also and more importantly there is no possible nuclear fusion reactions because nearly everything is already neutrons or even quarks. Just no energy sources large enough get any mass away.

This is in contrast to a white dwarf as it goes over the limit. As it starts collapsing toward a neutron star, the increased pressure/temperature sets of nuclear fusion (H->He, He-> C,) that runs-away and releases enough energy to detonate the object as a type I supernova.