An exotic star is a hypothetical compact star composed of something other than electrons, protons, and neutrons balanced against gravitational collapse by degeneracy pressure or other quantum properties. These include strange stars (composed of strange matter) and the more speculative preon stars (composed of preons).
Exotic stars are hypothetical, but observations released by the Chandra X-Ray Observatory on April 10, 2002 detected two candidate strange stars, designated RX J1856.5-3754and 3C58, which had previously been thought to be neutron stars. Based on the known laws of physics, the former appeared much smaller and the latter much colder than they should, suggesting that they are composed of material denser than neutronium. However, these observations are met with skepticism by researchers who say the results were not conclusive.
Quark stars and strange stars
If neutrons are squeezed enough at a high temperature, they will decompose into their component quarks, forming what is known as a quark matter. In this case, the star will shrink further and become denser, but instead of a total collapse into a black hole, it is possible, that the star may stabilize itself and survive in this state indefinitely, as long as no extra mass is added. It has, to some extent, become a very large nucleon. A star in this hypothetical state is called a quark star or more specifically a strange star. The pulsars RX J1856.5-3754 and 3C58 have been suggested as possible quark stars. Most neutron stars are thought to hold a core of quark matter, but it has proven hard to determine observationally.
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A preon star is a proposed type of compact star made of preons, a group of hypothetical subatomic particles. Preon stars would be expected to have huge densities, exceeding 1023 kilogram per cubic meter – intermediate between quark stars and black holes. Preon stars could originate from supernova explosions or the big bang; however, current observations from particle accelerators speak against the existence of preons.
Q stars are hypothetical compact, heavier neutron stars with an exotic state of matter where particle numbers are preserved. Q stars are also called “gray holes”.
An electroweak star is a theoretical type of exotic star, whereby the gravitational collapse of the star is prevented by radiation pressure resulting from electroweak burning, that is, the energy released by conversion of quarks to leptons through the electroweak force. This process occurs in a volume at the star’s core approximately the size of an apple, coleycontaining about two Earth masses.