Why is neutron star interesting to physics ?

[Leonardo Machado]

I've seen many people who is studying it.. but why ? is there any contributions to physics at a foundamentalist level ? I mean, the properties of matter inside nêutron stars is the interesting part to theoretical physics and not the whole object right ?

 

[phyzguy]

There are many reasons. Some people are interested in studying the properties of matter at these extreme densities. Others are interested in studying the enormous magnetic fields (as high as 10^15 Gauss) that some neutron stars have. Spinning neutrons stars are some of the most accurate "clocks" in the universe. Some people are studying how to use arrays of these accurate clocks to measure gravitational waves. Still others are studying how the radiation that we see is produced. Yet another interesting phenomenon is that neutron stars appear to have "starquakes" where the crust changes state that release enormous amounts of energy. We've also heard recently that many scientists think that the heaviest elements are produced from "decompressed" neutron star matter that is flung into space when two neutron stars merge. I could go on...

 

[mfb]

The first and most important reason: They exist. If something exists, we want to understand it.

Applications elsewhere can be interesting as well, but then you can ask what are the applications of these? What are the applications of gravitational waves?

There is no known application of things we can learn from neutron stars for everyday life on Earth today. That doesn't mean there cannot be applications, but if there are we first have to find them. To have a chance to find them, we have to study neutron stars. History is full of applications that came from fields where no application was expected.

 

[newjerseyrunner]

Another interesting thing is that neutron stars are little brothers of a theoretical object called quark stars that nobody has found yet.

 

[|Glitch|]

Another interesting thing is that neutron stars are little brothers of a theoretical object called quark stars that nobody has found yet.

Or perhaps we have found them, but we call them something else - like black holes, for example.

 

[newjerseyrunner]

Or perhaps we have found them, but we call them something else - like black holes, for example.

No, quark stars are held up by quark degeneracy pressure and will still glow with radiation. Black holes have collapsed beyond that.

We may have found some, but think they are neutron stars because they’d be nearly indistinguishable from each other.

 

[|Glitch|]

No, quark stars are held up by quark degeneracy pressure and will still glow with radiation. Black holes have collapsed beyond that.

We may have found some, but think they are neutron stars because they’d be nearly indistinguishable from each other.

They may still glow with radiation, but if their density makes them smaller than their Schwarzschild radius then nobody is going to be able to see that glowing radiation.

According to the Tolman-Oppenheimer-Volkoff limit, neutron stars become black holes once they exceed 3 solar masses. The largest neutron star we've discovered thus far was PSR J1614–2230 at ~1.97 solar masses. The least massive black hole yet discovered was XTE J1650-500 at 3.8 ± 0.5 solar masses. Quark stars would have to appear in that 1.83 solar mass range difference between the neutron stars and black holes that we know about. They would be denser than neutron stars, but not as dense as black holes. The real question is whether or not a quark star would be dense enough to be smaller than its Schwarzschild radius?

 

[mfb]

but if their density makes them smaller than their Schwarzschild radius

... then they are black holes and collapse.

 

[newjerseyrunner]

Yeah, you can’t have a quark star inside of a black hole because the Schwartzschild radius is where all paths point in so there is no causal way that any kind of pressure could continue to hold it up. A quark star would have to be a very specific size but would be categorically different than a neutron star.