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An Ongoing Cosmic Collision
NGC 5256, Markarian 266
RA 13h 38m 17.78s Dec 48° 16' 33.21"
350 million light years
1.2 × 1.1 arcmin
2.26 x 2.26 arcminutes
North is 28.7° left of vertical
December 14, 2017
2008 Image: G0816
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ABOUT THIS IMAGE:
A riot of color and light dances through this peculiarly shaped galaxy, NGC 5256. Its smoke-like plumes are flung out in all directions and the bright core illuminates the chaotic regions of gas and dust swirling through the galaxys center. Its odd structure is due to the fact that this is not one galaxy, but two in the process of a galactic collision.
NGC 5256, also known as Markarian 266, was discovered by William Herschel on May 12, 1787. It is about 350 million light-years away from Earth, in the constellation of Ursa Major (The Great Bear) . It is composed of two disc galaxies whose nuclei are currently just 13,000 light-years apart. Their constituent gas, dust, and stars are swirling together in a vigorous cosmic blender, igniting newborn stars in bright star formation regions across the galaxy.
Interacting galaxies can be found throughout the Universe, producing a variety of intricate structures. Some are quiet, with one galaxy nonchalantly absorbing another. Others are violent and chaotic, switching on quasars, detonating supernovae, and triggering bursts of star formation.
While these interactions are destructive on a galactic scale, stars very rarely collide with each other in this process because the distances between them are so vast. But as the galaxies entangle themselves, strong tidal effects produce new structures like the chaotic-looking plumes of NGC 5256 before settling into a stable arrangement after millions of years.
In addition to the bright and chaotic features, each merging galaxy of NGC 5256 contains an active galactic nucleus, where gas and other debris are fed into a hungry supermassive black hole. Observations from NASAs Chandra X-ray Observatory show that both of these nuclei and the region of hot gas between them have been heated by shock waves created as gas clouds collide at high velocities.
Galaxy mergers, like the one NGC 5256 is currently experiencing, were more common early in the Universe and are thought to drive galactic evolution. Today most galaxies show signs of past mergers and near-collisions. Our own Milky Way too has a long history of interaction: it contains the debris of many smaller galaxies it has absorbed in the past; it is currently cannibalizing the Sagittarius Dwarf Spheroidal Galaxy; and in a kind of cosmic payback, the Milky Way will merge with our neighbor, the Andromeda Galaxy in about two billion years.
Also in this Hubble image is another pair of probably interacting galaxies they are hiding to the right of NGC 5256 in the far distance, and have not yet been explored by any astronomer. From our perspective here on Earth, NGC 5256 is also just a few degrees away from another famous pair of interacting galaxies, Messier 51, which was observed by Hubble in 2005 (heic0506).
 NGC 5256 has previously been imaged by Hubble as part of a collection of 59 images of merging galaxies, released on Hubbles 18th anniversary on April 24, 2008. This new image adds H-alpha data taken from the Wide-Field Camera 3 to the previously available data, making the gas visible.