QUARK — STAR FORMATION
Neutrons are not fundamental particles.Since they are made of even smaller particles , called quarks. Neutron composed of an up- quark & two down-quarks .
Image credit NASA
As in neutron-star , due to enough pressure and temperature, electrons are crushed to protons to form a stellar core of neutrons, similarly, if there is enough pressure and temperature is subjected to neutron stellar core,it reverts to a core of quarks. we called it as quark-star .
In 1965 Soviet physicist duo D D Ivanenko & D Kurdgelaidze proposed the existence of the quark stars. Physicists believe that it is a metastable state between a neutron star & a black hole. Since, to form a quark star, it should be large enough to collapse beyond a neutron star but small enough to form a black hole.
Since quarks do not exist separately, due to a phenomenon called ' @ quark- confinement .The @strong nuclear force which binds quarks together in nuclei, actually increases with a distance,if we pull two quarks apart, force pulling them back increases,such that eventually attractive energy between them is so large that new particles appear in the vacuum.so to make up stellar objects out of up & down quarks ,that object would explode very quickly. But if strange quarks , which are very heavy & so short lived, quickly decay into up & down quarks, so physicists have found that if strange quarks can bind with up & down quarks to form a strangelets , under extreme pressure it would be stable object & this extreme pressure can be found in stellar core.
But do these strange quark stars exist ? physicists do not fully understand the physics of quark stars, they don't know even precise mass range , where these stars could exist.
However, some of the evidence, in favour of these exotic stellar objects. Like, Gaia space observatory & XMM- Newton x ray space telescope observed Neutron star is at the centre of supernova remnant called HESS J1731-347 is about 8150 light years from the earth. Astronomers found some of its data , radius is about 10.4 km & surface temperature approximately 2 M °k , which is quite typical for neutron stars, but its mass is equal to only 77% of mass of the sun, which puzzled astronomers, since it's almost 1.5 times less than theortical limit . A possible explanation is that, it was not a neutron star but a quark star.
In the 2008 observation of supernovae SN 2006gy, SN 2005gj & SN 2005ap also suggests the possible existence of a quark star.
In 2022, astronomers looked at GW 190425, a gravitational wave event due to the merger of two netron stars . It produced a kilonova , which is an explosion more powerful than a Nova ,but weaker than a supernova, it could be a quark star.
Although astronomers found evidence of quark stars, physicists are sceptical about their existence,due to very little observation evidence so far they have .