Why isnt the universe full of quark stars?

[Mustang11]

Hi all. I am curious as to why quark stars have not dominated by now, given their inability to decay as they are a mass of fundamental particles. What prevents this?

 

[Chalnoth]

They probably don't exist. The theoretical motivation is weak, and we have no observational evidence in support of their existence.

 

[mathman]

What is the distinction between a quark star and a neutron star? Neutrons are made of quarks.

 

[rootone]

What is the distinction between a quark star and a neutron star? Neutrons are made of quarks.

I gather that a hypothetical quark star would consist of disassociated quarks instead of triplets composing neutrons.
However I also gather that the existence free quarks in this manner is inconsistent with several well accepted theories.

 

[Chalnoth]

What is the distinction between a quark star and a neutron star? Neutrons are made of quarks.

As rootone stated, the form of matter is different. Instead of just a bunch of neutrons, it'd be sort of like a single giant nucleon consisting of huge numbers of quarks. It would be a hypothetical intermediate stage between a neutron star and a black hole.

However, if this form of matter does exist, it is predicted that it would actually be more stable than any other matter, so that any matter which came in contact with the quark star stuff would become quark star stuff. Thus, if we had a quark star implode (to become a black hole after collecting too much matter), and some of the material of that quark star escaped, then it would convert anything it came into contact with.

I think this is a pretty good reason to believe that quark stars don't exist.

 

[fzero]

Quark stars and quark matter are hypothetical, but I'm unaware of any strong objections to the possibility that they could exist. Quark matter would exist at extremely high temperatures and pressure, where the quarks are asymptotically free, so there is no reason for them to assemble into neutrons. It would be like shoving a huge amount of quark-gluon plasma into a small volume. If some quark matter were ejected from the implosion of a quark star, the ejected components would not necessarily be at the pressure required to remain quark matter and would probably stablize as ordinary matter.

 

[rootone]

If they did exist though they would probably be pretty much invisible to us, at least with any instrumentation we presently have.
Black holes may indeed be more easily detected through their indirect effects than quark stars would be.
Maybe there is some hope yet for massive compact halo objects being the explanation of dark matter.
*mods* - This is not a personal theory, please set your phasers on stun only.

 

[Chalnoth]

Quark stars and quark matter are hypothetical, but I'm unaware of any strong objections to the possibility that they could exist. Quark matter would exist at extremely high temperatures and pressure, where the quarks are asymptotically free, so there is no reason for them to assemble into neutrons. It would be like shoving a huge amount of quark-gluon plasma into a small volume. If some quark matter were ejected from the implosion of a quark star, the ejected components would not necessarily be at the pressure required to remain quark matter and would probably stablize as ordinary matter.

According to the models, quark matter is more stable at any pressure.

 

[PeterDonis]

According to the models, quark matter is more stable at any pressure.

But at low temperatures, quarks are not asymptotically free; wouldn't they form hadrons? Certainly that happens to quarks inside accelerators like the LHC when they are ejected from collisions--that's how quarks are spotted, by the hadron jets they produce.

 

[fzero]

According to the models, quark matter is more stable at any pressure.

I would tend to side with PeterDonis, that the ejected matter would be like jets. I am not doubting your statement about the pressure, but could you suggest an up-to-date reference on the equation of state? I'm sure some progress has been made since I've read anything about it.

 

[Chalnoth]

But at low temperatures, quarks are not asymptotically free; wouldn't they form hadrons? Certainly that happens to quarks inside accelerators like the LHC when they are ejected from collisions--that's how quarks are spotted, by the hadron jets they produce.

Here's a review:
http://arxiv.org/abs/astro-ph/0407155

See the section on strange quark matter in particular. The speculation is that because of the extra degree of freedom from the strange quark, this would be the true ground state of strong interactions. I don't think it's a very likely possibility, but it is fun to think about.

 

[PeterDonis]

Here's a review:
http://arxiv.org/abs/astro-ph/0407155

Thanks! I'll take a look.