What is the difference between a quark star and a neutron stars?

A quark star is really an intermediate stage in between neutron stars and black holes. It has too much mass at its core for the neutrons to hold their structure, but it doesn’t have enough to fully collapse into a black hole. The underlying quarks that form the neutrons are further compressed in these objects.

A quark star is also a hypothetical type of compact exotic star, where extremely high temperature and pressure has forced nuclear particles to form a continuous state of matter that consists primarily of free quarks. Also known as “strange” stars, quark stars may be the result, being smaller and denser than neutron stars, possibly explaining some abnormally bright supernovae seen recently while a neutron star is a giant star's collapsed core which, before its' collapse, had a total of between 10 and 29 solar masses. Neutron stars have a radius of the order of 10 kilometers (6.2 mi) and a mass lower than a 2.16 solar masses.

There are different speculations about how neutron stars form but the most common theory that is being stated is that neutron stars are formed after a supernova occurs. The remaining protons and electrons fuse with each other so neutrons are formed. It can be different for quark stars.

A quark star is often referred to as a hypothetical star which means that this type of star is not known to exist in actual at present time. This type of star is supposed to have a high temperature. It is also supposed to provide free quarks. Once again, this type of star is hypothetical. There is a big possibility that it will not exist. If it does, it has not been found yet.