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 The ''Atlas of Peculiar Galaxies'' is a catalog of peculiar galaxies produced by Halton Arp in 1966. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institute of Technology. The ...

''.

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: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten mo ...

to be dominated by the

far-infrared Far infrared (FIR) is a region in the infrared spectrum of electromagnetic radiation. Far infrared is often defined as any radiation with a wavelength of 15 micrometers (μm) to 1 mm (corresponding to a range of about 20 THz to ...

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. HST 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 clusters 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 ( sa, चन्द्र, Candra, shining' or 'moon), also known as Soma ( sa, सोम), 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) a ...

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 cornerst ...

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 has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not prod ...

(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 (JCMT). Arp 220 and other relatively local ULIRGs are being studied as equivalents of this kind of object. Astronomers from the Arecibo Observatory have detected organic molecules in the galaxy. Arp 220 contains at least two bright maser sources, an OH

megamaser A megamaser is a type of astrophysical maser, which is a naturally occurring source of stimulated spectral line emission. Megamasers are distinguished from other astrophysical masers by their large isotropic luminosity. Megamasers have typical ...

, and a water maser. In October 2011, astronomers spotted a record-breaking seven supernova 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 Interacting galaxies Starburst galaxies IC objects 09913 55497

220 __NOTOC__ Year 220 ( CCXX) was a leap year starting on Saturday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Antonius and Eutychianus (or, less frequently, year 973 '' ...

18660504 20111002 Luminous infrared galaxies Serpens (constellation)