Stephan's Quintet
Encyclopedia
Stephan's Quintet in the constellation Pegasus
is a visual grouping of five galaxies
of which four form the first compact galaxy group ever discovered. The group was discovered by Édouard Stephan in 1877 at Marseilles Observatory.
The group is the most studied of all the compact galaxy groups. The brightest member of the visual grouping is NGC 7320 that is shown to have extensive H II region
s, identified as red blobs, where active star formation is occurring.
92, and are involved in a cosmic dance that most likely will end with the galaxies merging. Radio observations in the early 1970s revealed a mysterious filament of emission which lies in inter-galactic space between the galaxies in the group. This same region is also detected in the faint glow of ionized atomic hydrogen seen in the visible part of the spectrum as the magnificent green arc in the picture to the right. Two space telescopes have recently provided new insight into the nature of the strange filament, which is now believed to be a giant intergalactic shock-wave (similar to a sonic boom but traveling in intergalactic gas rather than air) caused by one galaxy (NGC 7318B) falling into the center of the group at several millions of miles per hour.
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
.
Spitzer Space Telescope
which detects infrared radiation. The molecular hydrogen emission, which is seen through infrared spectral analysis using the Spitzer Space Telescope
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 includes 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. Most notable is the fact that this collision can help provide a view into what happened in the postulated beginning of the universe some 14 billion years ago, since shocked molecular hydrogen is likely to be present in the early universe.
(790 km/s) while the other four exhibit large redshifts (near 6600 km/s). Since galactic redshift is proportional to distance, NGC 7320 is only a foreground projection and is ~39 million ly from Earth versus the 210-340 million ly of the other five.
NGC 7319
has a type 2 Seyfert
nucleus.
Pegasus (constellation)
Pegasus is a constellation in the northern sky, named after the winged horse Pegasus in Greek mythology. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations.-Stars:...
is a visual grouping of five galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...
of which four form the first compact galaxy group ever discovered. The group was discovered by Édouard Stephan in 1877 at Marseilles Observatory.
The group is the most studied of all the compact galaxy groups. The brightest member of the visual grouping is NGC 7320 that is shown to have extensive H II region
H II region
An H II region is a large, low-density cloud of partially ionized gas in which star formation has recently taken place. The short-lived, blue stars forged in these regions emit copious amounts of ultraviolet light, ionizing the surrounding gas...
s, identified as red blobs, where active star formation is occurring.
Description
These galaxies are of interest because of their violent collisions. Four of the five galaxies in Stephan's Quintet form a physical association, Hickson Compact GroupHickson Compact Group
A Hickson Compact Group is a collection of galaxies designated as published by Paul Hickson in 1982.The most famous group on Hickson’s list of 100 objects is HCG 92, Stephan's Quintet....
92, and are involved in a cosmic dance that most likely will end with the galaxies merging. Radio observations in the early 1970s revealed a mysterious filament of emission which lies in inter-galactic space between the galaxies in the group. This same region is also detected in the faint glow of ionized atomic hydrogen seen in the visible part of the spectrum as the magnificent green arc in the picture to the right. Two space telescopes have recently provided new insight into the nature of the strange filament, which is now believed to be a giant intergalactic shock-wave (similar to a sonic boom but traveling in intergalactic gas rather than air) caused by one galaxy (NGC 7318B) falling into the center of the group at several millions of miles per hour.
X-ray source
As NGC 7318BNGC 7318
NGC 7318 are a set of galaxies about 300 million light-years away in the Constellation Pegasus...
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
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
Chandra X-ray Observatory
Chandra X-ray Observatory
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
.
Molecular hydrogen emission
Perhaps even more unexpected is the discovery of very powerful molecular hydrogen signals from the shock wave, seen by the NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
which detects infrared radiation. The molecular hydrogen emission, which is seen through infrared spectral analysis using the Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
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
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...
and includes 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. Most notable is the fact that this collision can help provide a view into what happened in the postulated beginning of the universe some 14 billion years ago, since shocked molecular hydrogen is likely to be present in the early universe.
Redshift
Also of interest, NGC 7320 (to the lower left in both photos) indicates a small redshiftRedshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...
(790 km/s) while the other four exhibit large redshifts (near 6600 km/s). Since galactic redshift is proportional to distance, NGC 7320 is only a foreground projection and is ~39 million ly from Earth versus the 210-340 million ly of the other five.
NGC 7319
NGC 7319
NGC 7319 is a spiral galaxy member of the Stephan's Quintet located in the constellation Pegasus.Controversially, the galaxy could "contain" a quasar. A quasar is an object conventionally thought to be incredibly farther away than an ordinary galaxy such as 7319. An article on the controversial...
has a type 2 Seyfert
Seyfert galaxy
Seyfert galaxies are a class of galaxies with nuclei that produce spectral line emission from highly ionized gas, named after Carl Keenan Seyfert, the astronomer who first identified the class in 1943...
nucleus.
Members
The five visually adjacent galaxies of Stephan's Quintet are NGC 7317–7320. NGC 7320, however, is a foreground object roughly 40 million ly away, significantly closer than the others at about 290 million ly, and not part of the Hickson association. The visual distinction between 7320 and the others in the 2009 HST image below is quite striking. A sixth galaxy, NGC 7320C, probably belongs to the association: it has a redshift similar to the Hickson galaxies, and a tidal tail appears to connect it with NGC 7319.| Name | Type | R.A. Right ascension Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:... (J2000) |
Dec. Declination In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and... (J2000) |
Redshift Redshift In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum... (km/s) |
Apparent Magnitude Apparent magnitude The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere... |
|---|---|---|---|---|---|
| NGC 7317 NGC 7317 NGC 7317 is a galaxy member of the Stephan's Quintet located in the constellation Pegasus.... |
E4 | 6599 ± 26 | +14.6 | ||
| NGC 7318a (UGC 12099) |
E2 pec | 6630 ± 23 | +14.3 | ||
| NGC 7318b (UGC 12100) |
SB(s)bc pec | 5774 ± 24 | +13.9 | ||
| NGC 7319 NGC 7319 NGC 7319 is a spiral galaxy member of the Stephan's Quintet located in the constellation Pegasus.Controversially, the galaxy could "contain" a quasar. A quasar is an object conventionally thought to be incredibly farther away than an ordinary galaxy such as 7319. An article on the controversial... |
SB(s)bc pec | 6747 ± 7 | +14.1 | ||
| NGC 7320c NGC 7320c NGC 7320c is a galaxy member of the Stephan's Quintet located in the constellation Pegasus.... |
(R)SAB(s)0/a | 5985 ± 9 | +16.7 | ||
External links
- A Shocking Surprise in Stephan's Quintet
- 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