Stephan’s Quintet, identified by Edouard Stephan in 1877, was the first
compact group of galaxies discovered. More recent study has convinced most
astronomers that of the 5 tightly packed galaxies at the middle of this image,
the blue one (NGC 7320) is probably not actually a member of the group, since
it seems to lie about 40 million light years from earth, while the other
galaxies are about 270 million light years from us. However, the Quintet can
keep its name, because it also seems likely that the galaxy in the upper
left (NGC 7320 C) actually belongs with the other 4 galaxies, and all are
engaged in a gravitational dance with one another. The galaxy in the middle
of the grouping (NGC 7318 B) seems to have already passed through the galaxy
to its left (NGC 7319), scattering a trail of stars and galactic gas out from
it (strangely, though the blue NGC 7320 seems to be very far from this cluster
and so unaffected by any of its galactic interactions, it also has its own trail
of debris – faintly visible in this image - roughly parallel with the stream
trailing out from NGC 7319). NGC 7318 B now seems to be more actively engaged
with another galaxy, NGC 7318 A, causing energetic new star formation, which
shows up as knots of new star clusters in the arms of both those galaxies.
NGC 7317 (at the lower right), like NGC 7320 C at the upper left, is staying
out of the action – for now.

This lovely and complex galactic collision is found in the constellation Pegasus.

This image was published in "Astronomy" magazine, November 2017, page 50.

Image detail:
Camera: SBIG STL-11000
Exposure: LRGB 420:60:60:60 (10 hours total)
Telescope: 12.5” Hyperion

Image taken Sept 22 & 28, Oct 3 & 5, 2013