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June 1990.

Galaxy Merger "The true nature of Arp 220, a peculiar 14th-magnitude galaxy in Serpens Caput, may finally be coming to light. For years astronomers have debated whether the system is a Seyfert galaxy, as its bright, active core suggests, or a starburst galaxy, as its very strong infrared emission would indicate....

"James R. Graham (California Institute of Technology) and colleagues made a very sharp 2.2-micron image using an infrared detector array on the 5-meter reflector atop Palomar Mountain. A special f/415 secondary mirror yielded an effective focal length of 2 kilometers....

"The resulting image ... shows two distinct sources barely 1 arc second apart [that] coincide with radio sources detected earlier at the Very Large Array.... This 'establishes beyond doubt that Arp 220 is the remnant of the merger of two galaxies,' says Graham, 'an event which triggered the ultraluminous phase now being witnessed.'"

The gravitational turmoil of this galactic merger seems responsible for the vigorous starforming activity being observed there, and it might in some way explain a surprise finding in 2011, namely, that Arp 220 spawns a supernova every few months.

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Title Annotation:75, 50 & 25 Years Ago; Arp 220 galaxy merging
Author:Sinnott, Roger W.
Publication:Sky & Telescope
Article Type:Brief article
Date:Jun 1, 2015
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