Cl0939+47 (Abell 851)
January 28, 1999
Row Res. (160 KB)
High Res. (1.5MB)
Object Name: Cl0939+47 (Abell 851)
Telescope: Subaru Telescope / Cassegrain Focus
Instrument: CISCO (J, K'), Suprime-Cam (R)
Filter: R (red), J (1.25 micron), K' (2.15 micron)
Color: Blue (R), Green (J), Red (K')
Date: UT 1999 Jan 13 (R), Jan 14 (J), Jan 12 (K')
Exposure: 3600 sec (R), 2400 sec (J), 2400 sec (K')
Field of View: 120 arcsec by 145 arcsec
Orientation: North up, east left
Position: RA (J2000.0)=09h43m, DEC (J2000.0)=+46d59m
Galaxies are not evenly distributed throughout the Universe, but tend to reside in structures ranging from groups of a few galaxies to massive clusters containing thousands of galaxies. This image of the distant cluster Abell 851, located five billion light years away from us, is about two million light years across. While the nearest sizable galaxy to our own, M 31 in Andromeda, is about two million light years away with mostly empty space in between, the same volume of space in Abell 851 is filled with many galaxies with a wide range of colors and sizes. Almost every object in this image is a galaxy, with there being only a few stars from our own Milky Way. All galaxy clusters contain bright, red elliptical galaxies, but distant clusters such as this also possess fainter blue galaxies, which are not seen in nearby ones. Both types are clearly visible in this color image, formed from optical and infrared images taken with Subaru' s Suprime-Cam and CISCO cameras. The depth and excellent quality of this image reveal a wealth of information never before seen from the ground.
By studying clusters of galaxies, astronomers hope to understand how individual galaxies form and evolve, as well as the history of the clusters themselves. Theoretical models predict that if the Universe contains enough material to stop its present expansion, then most clusters should have formed very recently. On the other hand, large numbers of distant, old clusters would imply that gravity is insufficient to overcome this expansion.