This portrait of Stephan’s Quintet, also known as the Hickson Compact Group 92, was taken by the ‘new’ Wide Field Camera 3 (WFC3) aboard the NASA/ESA Hubble Space Telescope. Stephan’s Quintet, as the name implies, is a group of five galaxies. The name, however, is a bit of a misnomer. Studies have shown that group member NGC 7320, at upper left, is actually a foreground galaxy that is about seven times closer to Earth than the rest of the group. Read the rest here at spacetelescope.org
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Credit: The fantastic Hubble Space Telescope and the incredible army of folks who make it all possible.
This small group of spiral galaxies was first discovered by the French astronomer, Edouard Stephan in 1877 and is often considered the prototype of small compact galactic groups.
It is the first of the compact groups found and probably the most investigated at all wavelengths. Initially Stephan included five relatively bright members (NGC 7317, 7318A/B, 7319, and 7320). In 1961 red shift measurements of the group revealed that NGC7320, the largest member of the group, had a discordant redshift and is receding at a velocity 5000 kilometers per second slower than the other four members.
A redshift is considered discordant if it differs from the median redshift of the group by more than 1000 kilometers per second. Although the case of NGC 7320 still fuels controversy it is generally agreed that all members of the group are gravitationally interacting with the exception of the interloper NGC 7320 which is a foreground galaxy.
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The first identified compact galaxy group, Stephan’s Quintet is featured in this remarkable image constructed with data drawn from Hubble Legacy Archive and the Subaru Telescope on the summit of Mauna Kea. The galaxies of the quintet are gathered near the center of the field, but really only four of the five are locked in a cosmic dance of repeated close encounters taking place some 300 million light-years away. The odd man out is easy to spot, though. The interacting galaxies, NGC 7319, 7318A, 7318B, and 7317 have a more dominant yellowish cast. They also tend to have distorted loops and tails, grown under the influence of disruptivegravitational tides. The mostly bluish galaxy, NGC 7320, is in the foreground about 40 million light-years distant, and isn’t part of the interacting group. Still, captured in this field above and to the left of Stephan’s Quintet is another galaxy, NGC 7320C, that is also 300 million light-years distant. Of course, including it would bring the four interacting galaxies back up to quintet status. Stephan’s Quintet lies within the boundaries of the high flyingconstellation Pegasus. At the estimated distance of the quintet’s interacting galaxies, this field of view spans over 500,000 light-years.
Image assembly & processing: Robert Gendler and Judy Schmidt Image data: Subaru Telescope (NAOJ), Hubble Legacy Archive, R. Gendler