Q star

Not to be confused with Q* or quark star.

A Q-star, also known as a grey hole, is a hypothetical type of 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 light, can escape.^[1] Light going in the opposite direction of the star’s center would be the most likely to escape from it, while light going in a direction almost parallel to its surface is the most likely not to escape. The Q stands for a conserved particle number. A Q-star may be mistaken for a stellar black hole.^[2] Some stellar black holes might be grey holes, two of which are V404 Cygni and Cygnus X-1. ^[1]

A simple diagram illustrating how some but not all light can escape from a grey hole

Types of Q-stars

• Q-ball^[3]
• B-ball, stable Q-balls with a large baryon number B. They may exist in neutron stars that have absorbed Q-ball(s).^[3]

See also

• Black hole
  • Stellar black hole
• Compact star
  • Exotic star
    • Boson star
    • Electroweak star
    • Preon star
    • Strange star
    • Quark star