Black Holes and Compact Objects

Compact objects are the dense remnants of stars that have exhausted their nuclear fuel. They include white dwarfs, neutron stars, and black holes, with each type formed depending on the original mass of the star.

• White dwarfs are the remnants of low- and medium-mass stars. They are supported against gravity by electron degeneracy pressure.
• Neutron stars form after the supernova explosion of more massive stars. They are extremely dense and are supported by neutron degeneracy pressure. Some neutron stars are observed as pulsars, emitting regular pulses of radiation.
• Black holes are formed when a very massive star collapses under its own gravity, creating a region where gravity is so strong that not even light can escape. The boundary of this region is called the event horizon.

Black holes are characterized mainly by their mass, spin (angular momentum), and electric charge (although astrophysical black holes are usually considered electrically neutral). They can be detected indirectly through their gravitational effects, the motion of nearby stars, gravitational lensing, X-ray emission from accreting matter, and gravitational waves produced during black hole mergers.