Star

Black dwarf star

A black dwarf is a theoretical stellar remnant, specifically a white dwarf that has cooled sufficiently that it no longer emits significant heat or light.

Main sequence star

A main sequence star is any star that is fusing hydrogen in its core and has a stable balance of outward pressure from core nuclear fusion and gravitational forces pushing inward.

Red supergiant star

A red supergiant is an aging giant star that has consumed its core's supply of hydrogen fuel. Helium has accumulated in the core, and hydrogen is now undergoing nuclear fusion in the outer shells. These shells then expand, and the now cooler star takes on a red color. They are the largest known stars.

Neutron star

a celestial object of very small radius (typically 18 miles/30 km) and very high density, composed predominantly of closely packed neutrons. Neutron stars are thought to form by the gravitational collapse of the remnant of a massive star after a supernova explosion, provided that the star is insufficiently massive to produce a black hole.

Protostar

a contracting mass of gas that represents an early stage in the formation of a star, before nucleosynthesis has begun.

Star

a massive ball of gas in outer space that gives off heat, light and other forms of radiation

Planetary nebula

a ring-shaped nebula formed by an expanding shell of gas around an aging star.

White dwarf star

a small very dense star that is typically the size of a planet. A white dwarf is formed when a low-mass star has exhausted all its central nuclear fuel and lost its outer layers as a planetary nebula.

Red giant star

a very large star of high luminosity and low surface temperature. Red giants are thought to be in a late stage of evolution when no hydrogen remains in the core to fuel nuclear fusion.

Stellar nebula star

the nebulosity surrounding a star : a star's shell or envelope of nebulosity