An ultraluminous infrared galaxy (ULIRG) emits most of its light in the infrared, and has a luminosity that is greater than a trillion Suns. Discovered by IRAS in 1983, the high luminosity of ULIRGs is created by the energy produced by widespread bursts of star formation (perhaps initiated by galaxy collisions), or by active galactic nuclei in the [..]

Active galactic nuclei (AGN) are the center of galaxies where black holes are thought to be the source of high luminosities. Such galaxies produce huge amounts of energy, exceeding the light emitted by all of the stars in the galaxy. A quasar is one particular type of AGN.

The average distance between the Earth and the Sun. 1 AU is 149,597,870.691 km (about 93 million miles). The Astronomical Unit is a constant which is used to measure distances within our solar system.

An object whose gravity is so strong that not even light can escape from it. Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun. If a star that massive or larger undergoes a supernova explosion, it may leave behind a fairly massive burned out stellar remnant. With no outward forces to oppose gravitatio [..]

A low-luminosty object with a mass that is intermediate between that of a star and a giant planet. With a mass of about 1-8% of the Sun, a brown dwarf is too small to ignite the thermonuclear fusion that defines a star. A theoretical entity until 1995, hundreds of these cool objects have been discovered in recent years.

A flattened, rotating disk of dust surrounding a star during the evolutionary stage when planets are being formed. At an earlier phase, a protoplanetary disk of dust may be mixed with gas from which the future planets will form.

Gas and dust found between the stars in a galaxy.

A measure of the heavy element (metal) content in stars and the interstellar medium (ISM). In the astronomical context, a metal refers to any atom heavier than helium. Metals result from the thermonuclear fusion of hydrogen and helium within stars, and are ejected into the ISM during the late stages of stellar evolution. The ISM is continually enri [..]

A star that brightens suddenly and to an unprecedented degree, creating the impression that a new star has appeared where none was before. Hence the name, from nova for "new."

A bubble of gas surrounding a hot,dying star. The star is so hot that it makes the planetary nebula glow, which allows astronomers to see it. The star was once the core of a red giant, which ejected its outer atmosphere and created the planetary nebula. A planetary nebula has nothing to do with a planet, but through a small telescope, it looks like [..]