Compact object
The state and type of a stellar remnant depends primarily on the mass of the star that it formed from.
In June 2020, astronomers reported narrowing down the source of Fast Radio Bursts (FRBs), which may now plausibly include "compact-object mergers and magnetars arising from normal core collapse supernovae".
All active stars will eventually come to a point in their evolution when the outward radiation pressure from the nuclear fusions in its interior can no longer resist the ever-present gravitational forces.
Compact objects have no internal energy production, but will—with the exception of black holes—usually radiate for millions of years with excess heat left from the collapse itself.
[3] According to the most recent understanding, compact stars could also form during the phase separations of the early Universe following the Big Bang.
Although compact objects may radiate, and thus cool off and lose energy, they do not depend on high temperatures to maintain their structure, as ordinary stars do.
Black holes are however generally believed to finally evaporate from Hawking radiation after trillions of years.
The equation of state for degenerate matter is "soft", meaning that adding more mass will result in a smaller object.
Continuing to add mass to what begins as a white dwarf, the object shrinks and the central density becomes even greater, with higher degenerate-electron energies.
If matter were removed from the center of a white dwarf and slowly compressed, electrons would first be forced to combine with nuclei, changing their protons to neutrons by inverse beta decay.
If further compressed, eventually it would reach a point where the matter is on the order of the density of an atomic nucleus – about 2×1017 kg/m3.
Electrons react with protons to form neutrons and thus no longer supply the necessary pressure to resist gravity, causing the star to collapse.
Once the star's pressure is insufficient to counterbalance gravity, a catastrophic gravitational collapse occurs within milliseconds.
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.
Most neutron stars are thought to hold a core of quark matter but this has proven difficult to determine observationally.
This process occurs in a volume at the star's core approximately the size of an apple, containing about two Earth masses.
However, it may become possible to detect them by the gravitational radiation emitted by a pair of co-orbiting boson stars.
[13][14] Based on the generalized uncertainty principle (GUP), proposed by some approaches to quantum gravity such as string theory and doubly special relativity, the effect of GUP on the thermodynamic properties of compact stars with two different components has been studied recently.
