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Sky merger yields
sparkling dividends

Posted: October 13, 2009

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The Hubble Space Telescope has captured an image of a striking galaxy, revealing the celestial oddity as the product of a high-speed galactic collision between two Milky Way-like galaxies.

NGC 2623 resides 250 million light years away in the constellation of Cancer. The data used for this colour composite were taken in 2007 by the Advanced Camera for Surveys (ACS) aboard Hubble. Image: NASA, ESA and A. Evans (Stony Brook University, New York & National Radio Astronomy Observatory, Charlottesville, USA).

The two galaxies, collectively known as NGC 2623 or Arp 243, are in the late stages of merging – their cores have amalgamated into one central nucleus. Two tidal tails rich with young stars stream out from the cores, a classic sign that a merger event has taken place and that material has been frantically exchanged between the two original galaxies.

NGC 2623's prominent lower tail is also richly populated with bright star clusters – one hundred of them have been found in these observations, some of which are brighter than the brightest clusters we see in our own local neighbourhood. Star clusters in this interacting pair likely formed as part of a loop of stretched material associated with the northern tail, or from debris falling back onto the nucleus.

Merger events may also result in the 'turning on' of an active galactic nucleus, where one of the supermassive black holes residing at the centres of the two original galaxies is stirred into action. Matter is drawn in toward the black hole and the energy released heats up the surrounding disc of material, lighting up the galaxy across a wide range of energies.

NGC 2623 is bright in the infrared and thus is a member of the very luminous infrared galaxies (LIRG) group. It has been extensively studied by the Great Observatories All-sky LIRG Survey (GOALS) project that combines data from space observatories such as Hubble, Spitzer, Chandra and the Galaxy Evolution Explorer (GALEX).