Arp 220 is the result of a collision between two galaxies which are now in the process of merging. It is the 220th object in Halton Arp's '' Atlas of Peculiar Galaxies''.

Features

The merging galaxy system Arp 220 from ALMA and Hubble

Arp 220 is the closest ultraluminous infrared galaxy (ULIRG) to Earth, at 250 million light years away. Its energy output was discovered by

IRAS The Infrared Astronomical Satellite (Dutch language, Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a astronomical survey, survey of the entire night sky at infrared wavelengths. Launched on 25 Janu ...

to be dominated by the far-infrared part of the spectrum. It is often regarded as the prototypical ULIRG and has been the subject of much study as a result. Most of its energy output is thought to be the result of a massive burst of star formation, or starburst, probably triggered by the merging of two smaller galaxies.

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

observations of Arp 220 in 2002 and 1997, taken in visible light with the ACS, and in infrared light with NICMOS, revealed more than 200 huge

star cluster A star cluster is a group of stars held together by self-gravitation. Two main types of star clusters can be distinguished: globular clusters, tight groups of ten thousand to millions of old stars which are gravitationally bound; and open cluster ...

s in the central part of the galaxy. The most massive of these clusters contains enough material to equal about 10 million suns. X-ray observations by the

Chandra Chandra (), also known as Soma (), is the Hindu god of the Moon, and is associated with the night, plants and vegetation. He is one of the Navagraha (nine planets of Hinduism) and Dikpala (guardians of the directions). Etymology and other ...

and

XMM-Newton ''XMM-Newton'', also known as the High Throughput X-ray Spectroscopy Mission and the X-ray Multi-Mirror Mission, is an X-ray space observatory launched by the European Space Agency in December 1999 on an Ariane 5 rocket. It is the second corners ...

satellites have shown that Arp 220 probably includes an

active galactic nucleus An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such e ...

(AGN) at its core, which raises interesting questions about the link between galaxy mergers and AGN, since it is believed that galactic mergers often trigger starbursts, and may also give rise to the supermassive black holes that appear to power AGN. Luminous far-infrared objects like Arp 220 have been found in surprisingly large numbers by sky surveys of submillimetre wavelengths using instruments such as the Submillimetre Common-User Bolometer Array (SCUBA) at the

James Clerk Maxwell Telescope The James Clerk Maxwell Telescope (JCMT) is a submillimetre-wavelength radio telescope at Mauna Kea Observatory in Hawaii, US. The telescope is near the summit of Mauna Kea at . Its primary mirror is 15 metres (16.4 yards) across: it is the la ...

(JCMT). Arp 220 and other relatively local ULIRGs are being studied as equivalents of this kind of object. Astronomers from the

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science F ...

have detected organic molecules in the galaxy. Arp 220 contains at least two bright maser sources, an OH megamaser, and a water maser. In October 2011, astronomers spotted a record-breaking seven

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

all found at the same time in Arp 220. The merging of the two galaxies started around 700 million years ago.

References

External links

"Hubble Sees Star Birth Gone Wild"
(''SpaceDaily'') Jun 16, 2006 * {{DEFAULTSORT:Arp 220 Spiral galaxies Galaxy mergers Starburst galaxies IC objects 09913 55497 220 18660504 20111002 Luminous infrared galaxies Serpens