At first glance, this latest image release from Hubble appears to be one really bizarre-looking galaxy. But actually, this is a pair of spiral galaxies that resemble our own Milky Way smashing together at breakneck speeds. The centers have already merged into one nucleus, and the two tidal tails stretching out from the center are sparkling with active star formation, prompted by the exchange of mass and gases from the dramatic collision. This object, NGC 2623, or Arp 243, is about 250 million light-years away in the constellation of Cancer (the Crab), and is in the late stages of the merging process.
The prominent lower tail is richly populated with bright star clusters — 100 of them have been found in these observations. The large star clusters that the team has observed in the merged galaxy are brighter than the brightest clusters we see in our own vicinity. These star clusters may have formed as part of a loop of stretched material associated with the northern tail, or they may have formed from debris falling back onto the nucleus. In addition to this active star-forming region, both galactic arms harbor very young stars in the early stages of their evolutionary journey.
Watch this video for more information on NGC 2623:
Some mergers (including NGC 2623) can result in an active galactic nucleus, where one of the supermassive black holes found at the centers of the two original galaxies is stirred into action. Matter is pulled toward the black hole, forming an accretion disc. The energy released by the frenzied motion heats up the disc, causing it to emit across a wide swath of the electromagnetic spectrum.
NGC 2623 is so bright in the infrared that it belongs to the group of very luminous infrared galaxies (LIRG) and has been extensively studied as the part of the Great Observatories All-sky LIRG Survey (GOALS) project that combines data from Hubble, the Spitzer Space Telescope, Chandra X-ray Observatory and the Galaxy Evolution Explorer (GALEX). The combination of resources is helping astronomers characterize objects like active galactic nuclei and nuclear star formation by revealing what is unseen at visible wavelengths.
The data used for this color composite were actually taken in 2007 by the Advanced Camera for Surveys (ACS) aboard Hubble, but is just being released now, as a team of over 30 astronomers, led by Aaron S. Evans, recently published an overview paper, detailing the first results of the GOALS project. Observations from ESA’s X-ray Multi-Mirror Mission (XMM-Newton) telescope contributed to the astronomers’ understanding of NGC 2623.
NGC 2623 paper
GOALS Overview paper
Source: European Hubble website