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14 December 2017
An ongoing cosmic collision
A riot of colour 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 galaxy’s centre. 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, 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.
NGC 5256 (ground-based view)
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 NASA’s 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.
Hubble Space Telescope
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 cannibalising the Sagittarius Dwarf Spheroidal Galaxy; and in a kind of cosmic payback, the Milky Way will merge with our neighbour, the Andromeda Galaxy in about two billion years.
Zoom on NGC 5256
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).
Pan across NGC 5256
 NGC 5256 has previously been imaged by Hubble as part of a collection of 59 images of merging galaxies, released on Hubble’s 18th anniversary on 24 April 2008. This new image adds H-alpha data taken from the Wide-Field Camera 3 to the previously available data, making the gas visible.
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
Images of Hubble:http://www.spacetelescope.org/images/archive/category/spacecraft/
ESA's Hubble website: http://www.spacetelescope.org/
NASA’s Chandra X-ray Observatory: http://chandra.si.edu/
Images, Animation, Text, Videos, Credits: NASA, ESA/Mathias Jäger/The Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University).
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