Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2011 December 23
See Explanation.  Clicking on the picture will download
 the highest resolution version available.

Shell Galaxy NGC 7600
Image Credit & Copyright: Ken Crawford (Rancho Del Sol Observatory)
Collaboration: Andrew Cooper (MPA), Carlos Frenk, John Helly, Shaun Cole (Institute for Computational Cosmology),
David Martinez-Delgado (MPIA), Star Stream Pilot Survey Group

Explanation: Similar in size to the Milky Way, elliptical galaxy NGC 7600 is about 160 million light-years distant. In this deep image, spanning about 1/2 degree on the sky toward the constellation Aquarius, NGC 7600 sports a remarkable outer halo of nested shells and broad circumgalactic structures. The tantalizing features can be explained by the accretion of dark matter and stars on a cosmic timescale. In fact, a movie generated by simulating galaxy formation using a cosmological model with cold dark matter for the halos of merging galaxies reproduces the appearance of NGC 7600 in amazing detail. The remarkable simulation movie is available here on Vimeo and here in other formats. It presents compelling evidence that detailed features of galaxy mergers observed with small, wide field telescopes on planet Earth, are natural consequences of galaxy formation and fundamental properties of dark matter.

Tomorrow's picture: Moon over the mountains

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