阿普220

阿尔普220（Arp 220）是两个星系相互碰撞后合并中的天体，距离地球约2.5亿光年，位于巨蛇座。名称来自它是霍尔顿·阿尔普编的《特殊星系图集》中的第220个天体。

概要

阿尔普220是距离地球最近的极亮红外星系。红外天文卫星发现它的辐射波段主要是在远红外线，因此常被认为是极亮红外星系的原型，并且是许多相关研究的主题。阿尔普220大部分的能量输出被认为是大量恒星形成的结果，并且这现象可能是因为两个较小星系合并引发。2002到2007年哈勃空间望远镜对阿尔普220使用先进巡天照相机进行可见光波段观测，以及近红外线照相机和多目标分光仪进行红外线波段观测，在它的中心部位发现了超过200个巨大星团。其中最巨大的星团内所含物质约有1000万倍太阳质量。钱德拉X射线天文台和XMM-牛顿卫星以X射线观测的结果显示阿尔普220的核心可能存在活动星系核，这产生了活动星系核和星系合并之间关联性的有趣问题。一般认为既然星系合并常造成星暴，也可能产生驱动活动星系核的特大质量黑洞。

天文学家使用詹姆士·克拉克·麦斯威尔望远镜搭载的亚毫米波通用测辐射计阵列进行次毫米波段巡天观测，结果意外发现跟阿尔普220一样的亮红外星系相当多。天文学家对阿尔普220和其他相对距离地球较近的极亮红外星系都进行了大量研究。

阿雷西博天文台的天文学家对阿尔普220进行观测发现该星系内有有机分子存在。

阿尔普220内至少有两个明亮的激微波源，其中一个是 OH 分子，另一个则是水分子激微波。

2011年10月，天文学家破纪录地在阿尔普220内同时发现了7颗超新星。

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

Arp 220 is the closest ultraluminous infrared galaxy (ULIRG) to Earth, at 250 million light years away. Its energy output was discovered by IRAS 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 observations of Arp 220 in 2002 and 1997, taken in visible light with the ACS, and in infrared light with NICM…

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, 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.