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.

The early Universe refers to approximately the first billion years after the Big Bang, which is estimated to have taken place about 14 billion years ago. Because of the expansion of the Universe, it also corresponds to the most distant reaches of the Universe.

A massive galaxy or cluster of galaxies that intervenes between us and a distant astronomical object and that gravitationally deflects the light from that distant object. Gravitational lenses can focus, distort, and split light beams in the same way that ordinary glass lenses do.

Gaseous nebulae which contain material at a temperature of about 10,000 degrees Kelvin. At this temperature hydrogen becomes ionized as its electrons break free.

Gas and dust found between the stars in a galaxy.