Q star

A Q-star, also known as a grey hole, is a hypothetical type of a compact, heavy neutron star with an exotic state of matter. Such a star can be smaller than the progenitor star's Schwarzschild radius and have a gravitational pull so strong that some light, but not all photons, can escape. The Q stands for a conserved particle number. A Q-star may be mistaken for a stellar black hole.

Types of Q-stars

 * Q-ball
 * B-ball, stable Q-balls with a large baryon number B. They may exist in neutron stars that have absorbed Q-ball(s).