Galaxies · Space Codex
Stephan's Quintet
Four galaxies about 290 million light-years away locked in repeated close encounters, plus a fifth, NGC 7320, much nearer and only in the same line of sight.
Four interacting galaxies and an interloper
At a glance
| Measure | Value | Source |
|---|---|---|
| Distance | About 290 million light-years (NGC 7320: about 40 million)ESA: ESA/Webb weic2208 (opens in a new tab) | ESA: ESA/Webb weic2208 (opens in a new tab) |
| Shock front | NGC 7318B is smashing through the groupESA: ESA/Webb weic2208 (opens in a new tab) | ESA: ESA/Webb weic2208 (opens in a new tab) |
| Active nucleus | NGC 7319's black hole, 24 million Suns, shines like 40 billion SunsESA: ESA/Webb weic2208 (opens in a new tab) | ESA: ESA/Webb weic2208 (opens in a new tab) |
| Webb image | Its largest at release (2022): about one-fifth of the Moon's diameterESA: ESA/Webb weic2208 (opens in a new tab) | ESA: ESA/Webb weic2208 (opens in a new tab) |
Key points
- One of Webb's first images (2022)
- Four galaxies in a gravitational dance
- One 'member' is a foreground interloper
A cosmic pile-up
One galaxy is ploughing through the group at high speed, heating gas into a vast shock front. Webb traced the debris and the outflow from NGC 7319's feeding black hole.
How it was found
The French astronomer Édouard Stephan spotted the group in 1877, the first compact group of galaxies ever recognised. Redshift measurements later showed that NGC 7320 lies about 40 million light-years away, roughly seven times nearer than the rest, so the true physical group, catalogued as Hickson Compact Group 92, consists of the other four. The quintet sits in Pegasus and needs a sizeable telescope and dark autumn skies to see at all.
A shock larger than a galaxy
In 2006 Spitzer found that the intruder NGC 7318B, slamming into gas in the group, has driven a shock front larger than the Milky Way, glowing with the most turbulent molecular hydrogen then seen. In 2024 the WEAVE spectrograph on the William Herschel Telescope, combined with LOFAR radio and archival Webb data, clocked the intruder at about 3.2 million km/h. The shock appears two-faced: it ionises cold gas it passes through, but only compresses the hotter gas, which then shines in radio waves.
What Webb added
Webb's mosaic, one of its first images in July 2022, combined NIRCam and MIRI data into more than 150 million pixels from almost 1,000 separate image files. It resolved individual stars and the bright core of foreground NGC 7320, traced tails of gas, dust and stars pulled out by repeated encounters, and used its spectrographs to measure fast outflows near the black hole in NGC 7319.
Why it matters
Tight groups like this may have been more common in the young universe, when gas falling into galaxies could feed brilliant quasars. Stephan's Quintet shows the same processes up close: tidal stripping, collision shocks and star formation triggered by encounters, all of which help explain how massive galaxies were assembled.
Missions
- 2021–
Infrared observatory at Sun–Earth L2, about 1.5 million km from Earth.
Related entries
- Cartwheel GalaxyA ring galaxy made by a collision
- Antennae GalaxiesTwo spirals merging
Sources
- NASA Spitzer ssc2006-08a: a shocking surprise in Stephan's Quintet (opens in a new tab)
- Arnaudova et al. 2024, MNRAS 535:2269, WEAVE first light on the Stephan's Quintet shock (arXiv) (opens in a new tab)
- ESA: ESA/Webb weic2208 (opens in a new tab)
Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.