Ultraluminous infrared galaxy

An ultraluminous infrared galaxy (ULIRG) emits more than one trillion times the Sun’s luminosity in infrared light. Its intense emission is usually powered by rapid star formation, accretion onto a supermassive black hole, or both.

Dust emission: Thermal radiation emitted by interstellar dust after it absorbs energy from stars or other sources. Dust absorbs much of a ULIRG’s visible and ultraviolet light and reradiates that energy in the infrared.
Galaxy merger: The gravitational interaction and eventual coalescence of two or more galaxies. Mergers can concentrate gas and trigger the intense activity seen in many nearby ULIRGs.
Infrared astronomy: The study of astronomical objects using infrared radiation. Infrared observations penetrate dust that conceals much of a ULIRG’s energy source.
Hyperluminous infrared galaxy: A galaxy with infrared luminosity above ten trillion times the Sun’s luminosity. HyLIRGs extend the infrared-luminosity sequence beyond the ULIRG range.
Starburst: A period of unusually rapid star formation in a galaxy. Compact bursts of star formation can supply much of a ULIRG’s heating power.
Major merger: A merger between galaxies of broadly comparable mass. Many classic ULIRGs are associated with major mergers that strongly disrupt their structure.
Infrared luminosity: The total energy a source emits per unit time in the infrared wavelength range. This quantity defines the ULIRG threshold and enables comparisons among dusty galaxies.
Quasar: An extremely luminous active galactic nucleus powered by accretion onto a supermassive black hole. A quasar is identified by powerful nucleus emission, while a ULIRG is classified by total infrared luminosity.
Active galactic nucleus: A luminous central region powered by matter accreting onto a supermassive black hole. An obscured active nucleus can contribute substantially to a ULIRG’s infrared output.
Tidal interaction: A gravitational encounter that distorts galaxies and redistributes their stars and gas. Tidal forces can funnel gas inward and help initiate a ULIRG phase.

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