Stephan's Quintet

Stephan's Quintet is a visual grouping of five galaxies of which four form the first compact galaxy group ever discovered.

The group is the most studied of all the compact galaxy groups.

Emissions

X-rays

thumb|300px|right|Stephan's Quintet. The blue arc across the top center is a shock caused by colliding intergalactic gas. Image Credits: X-ray (blue): NASA/CXC/CfA/E. O'Sullivan Optical (brown): Canada-France-Hawaii-Telescope/Coelum

As NGC 7318B collides with gas in the group, a huge shock wave bigger than the Milky Way spreads throughout the medium between the galaxies, heating some of the gas to temperatures of millions of degrees where they emit X-rays detectable with the NASA Chandra X-ray Observatory.

Molecular hydrogen emission

The NASA Spitzer Space Telescope, which detects infrared radiation, discovered a very powerful molecular hydrogen signal from the shock wave between the galaxies. This emission is one of the most turbulent formations of molecular hydrogen ever seen, and the strongest emission originates near the center of the green area in the visible light picture discussed earlier. This phenomenon was discovered by an international team led by scientists at the California Institute of Technology and including scientists from Australia, Germany and China. The detection of molecular hydrogen from the collision was initially unexpected because the hydrogen molecule is very fragile and is easily destroyed in shock waves of the kind expected in Stephan's Quintet. However, one solution is that when a shock front moves through a cloudy medium like the center of the group, millions of smaller shocks are produced in a turbulent layer, and this can allow molecular hydrogen to survive.

thumb|Earthbound monochrome (sdss-g filtered) image of Stephan's Quintet from the [[Liverpool Telescope]]

Redshift

NGC 7320 indicates a small redshift (790 km/s) while the other four exhibit large redshifts (near 6,600 km/s). Since galactic redshift is proportional to distance, NGC 7320 is only a foreground projection

NGC 7319 has a type 2 Seyfert nucleus.

500px|thumb|center|alt=Photo of the area of the Hubble photo, with the various galaxies labeled by NGC number|The galaxies in the vicinity of Stephan's Quintet. The rectangle indicates the area covered by the 1998–99 [[:File:StephansQuintet3.jpg|Hubble Space Telescope image below.]]

A sixth galaxy, NGC 7320C, probably belongs to the Hickson association: it has a redshift similar to the Hickson galaxies, and a tidal tail appears to connect it with NGC 7319.

thumb|Detail of the quintet in a photo by [[Hubble Space Telescope, 1998–99. Credits: NASA/ESA]]

Infrared

Using its Mid Infrared Instrument (MIRI), the James Webb Space Telescope shows details shrouded by dust in visible light including large shock waves and tidal tails in four of the five galaxies, and previously hidden areas of star formation. These new details will contribute to insights on galaxy evolution.

thumb|center|Four galaxies (Missing is NGC 7317) of Stephan's Quintet using MIRI by [[James Webb Space Telescope]]

Members

{| class="wikitable" style="text-align:center;"

|+Members of the Hickson Compact Group 92

! Name

! Type

! R.A. (J2000)

References

External links

GALEX: Stephan's Quintet and NGC 7331
Star Clusters Born in the Wreckage of Cosmic Collisions
News Release at ESA/Hubble
Stephan's Quintet
NightSkyInfo.com : Stephan's Quintet
What's Behind Stephan's Quintet? Peter Edmonds, Chandra Blog, 21 July 2009
Astronomy Picture of the Day on Stephan's Quintet: 13 Nov 2000   12 Aug 2003   11 Sep 2009
NASA’s James Webb Space Telescope reveals never-before-seen details of the galaxy group called “Stephan’s Quintet.”