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Astro: Hubble 21st anniversary image release

Posted 4/27/2011 12:04 AM by Ka Chun Yu | Comments

To celebrate the 21st anniversary of the Hubble Space Telescope, a spectacular image of the pair of colliding galaxies Arp 273 was released. Click on the image to get a super-enormous 4000-pixel wide version of the image (or this link for the full-size TIFF at roughly 8000 pixels across, and 120 MB in size):

Although the pair is known as Arp 273, the individual galaxies are UGC 1810 (top) and UGC 1813 (bottom).

Most galaxies reside in clusters.  The distances between them may be typically tens to hundreds of galactic diameters.  Hence near-misses, collisions, and mergers are quite common as galaxies orbit collectively around themselves in the cluster.  (This isn't the case for the stars inside the galaxies.  The stellar distances are millions of times larger than stellar diameters, so stellar mergers and near-misses are far rarer for all of the stars within a pair of colliding galaxies like above.)

The gravitational interplay between the pairs of galaxies lead to the tidal tails of stars that seem to bridge the two.  The larger galaxy's outer spiral arm is wrapping around itself, almost completing a ring around the galaxy.  The close pass has also disrupted the clouds of dark molecular gas and dust.  Instead of neatly following the spiral arms, they are spread out.  Some of it has been pushed and compressed, with clumps of clouds collapsing to form clusters of young stars.

A periodic series of stellar clusters can be seen running horizontally across the top of UGC 1810.  Different telescope filters were used to create the color composite from Hubble's Wide Field Camera 3.  Here the blue color represents ultraviolet (UV) radiation from young, massive stars, which live fast, and die young.  The winds and outflows from these and other young stars disrupt the molecular gas surrounding them in their natal environment.  Massive stars blowing up as supernovae can finish off the clouds, leaving the remaining young stars in the cluster -- now unbounded by the gravity of the parent cloud -- to spread out and percolate in their orbits through the rest of the galactic disk.

In addition to a fascinating snapshot into the collision and mergers of these galaxies (which can take hundreds of millions to billions of years), a picture like this also reveals all of the activity that goes on in galaxies.  There are hints of star birth, star death, and the cycling of matter as it goes from molecular clouds to stars and back into the interstellar medium.

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