Pictures of galaxy clusters and galaxy groups

A guide to galaxy clusters and groups, and images of these gigantic cosmic structures.

Galaxy clusters are collections of gravitationally-bound galaxies and are the largest known structures held together by gravity in the Universe.

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Galaxy groups are similarly gigantic, but they generally contain fewer galaxies and are not as large as galaxy clusters.

Galaxy clusters

Fornax Galaxy Cluster by Rafael Compassi, Presidente Lucena, Brazil. Equipment: 80mm F/5 Triplet APO, QHY9m, 36mm Baader filters.
Fornax Galaxy Cluster by Rafael Compassi, Presidente Lucena, Brazil. Equipment: 80mm F/5 Triplet APO, QHY9m, 36mm Baader filters.

Galaxy clusters can contain up to thousands of galaxies and are fascinating objects for astronomers and cosmologists to observe because studying them reveals information about the hidden secrets of the Universe.

They are vital targets for understanding the properties of dark matter, for example.

Dark matter is the name given to the mysterious, invisible substance that accounts for about 85% of all matter in the Universe.

It cannot be directly observed, but astronomers can infer its existence because of its gravitational influence on visible matter.

Dark matter accounts for 85% of the total mass of a galaxy cluster: the galaxies themselves make up just 2% of the total mass.

In the case of galaxy clusters, the total visible mass is not enough to account for the gravity required to hold them together, given the speed at which they travel.

Extra mass in the form of hot gas known as the intracluster medium does account for some of the extra gravity required to hold the galaxy clusters together, but it’s still not enough.

The extra missing material is known as dark matter.

Famous galaxy clusters beloved by astronomers and astrophotographers include the Virgo Cluster, the Fornax Cluster and the Hercules Cluster.

Galaxy Groups

M96 Group of Galaxies by Jeffrey O. Johnson, Las Cruces, New Mexico, USA. Equipment: Takahashi FS-60C, Takahashi EM200 Temma II, QSI 540wsg , SX Lodestar.
M96 Group of Galaxies by Jeffrey O. Johnson, Las Cruces, New Mexico, USA. Equipment: Takahashi FS-60C, Takahashi EM200 Temma II, QSI 540wsg , SX Lodestar.

Galaxy groups are much smaller than galaxy clusters, but there is no clear dividing line between the two. Galaxy groups generally contain up to 50 galaxies gravitationally bound.

Our own galaxy the Milky Way is found in the Local Group of galaxies, along with the Andromeda Galaxy and the Triangulum Galaxy.

Below is a selection of images of galaxy clusters captured by BBC Sky at Night Magazine.

For more info on deep-sky imaging, read our guide on deep-sky astrophotography and deep-sky image processing.

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And don’t forget to send us your images or share them with us via Facebook, Twitter and Instagram.

The Virgo Cluster by Rob Little, Corbridge, UK. Equipment: ATIK 383L CCD, Badder 36mm RGB and Ha filters, Borg 77 EDII APO, NEQ6 mount.
The Virgo Cluster by Rob Little, Corbridge, UK. Equipment: ATIK 383L CCD, Badder 36mm RGB and Ha filters, Borg 77 EDII APO, NEQ6 mount.
Draco Trio by Dan Crowson, Animas, New Mexico, UK. Equipment: SBIG STF-8300M, Astro-Tech AT12RCT.
Draco Trio by Dan Crowson, Animas, New Mexico, UK. Equipment: SBIG STF-8300M, Astro-Tech AT12RCT.
NGC4216 and Friends by Ron Brecher, Ontario, Canada. Equipment: SBIG STL-11000M, Baader LRGB, 10
NGC4216 and Friends by Ron Brecher, Ontario, Canada. Equipment: SBIG STL-11000M, Baader LRGB, 10″ ASA astrograph, Paramount MX, QHY5, 80mm refractor, FocusMax, TheSkyX.
NGC4216 and Friends by Ron Brecher, Ontario, Canada. Equipment: SBIG STL-11000M, Baader LRGB, 10
NGC4216 and Friends by Ron Brecher, Ontario, Canada. Equipment: SBIG STL-11000M, Baader LRGB, 10″ ASA astrograph, Paramount MX, QHY5, 80mm refractor, FocusMax, TheSkyX.
Three Messiers in Virgo by Dan Crowson, Missouri, USA. Equipment: SBIG ST-8300M, Astro-Tech AT90DT
Three Messiers in Virgo by Dan Crowson, Missouri, USA. Equipment: SBIG ST-8300M, Astro-Tech AT90DT
C30 and 23 Other Galaxies by Andy Smith, Chatham, Kent, UK. Equipment: SkyWatcher 100ED, CG-5 mount, F/8.5 Focal Reducer, Canon 1100D, BackyardEOS, Orion MMAG
C30 and 23 Other Galaxies by Andy Smith, Chatham, Kent, UK. Equipment: SkyWatcher 100ED, CG-5 mount, F/8.5 Focal Reducer, Canon 1100D, BackyardEOS, Orion MMAG
NGC 7331 Galaxy Group by Dean Ashton, St Austell, Cornwall, UK. Equipment: 235mm Celestron EdgeHD SCT, CGEM Mount, Celestron Nightscape 10100 OSC CCD, LoadstarX2 guide camera, off axis guider.
NGC 7331 Galaxy Group by Dean Ashton, St Austell, Cornwall, UK. Equipment: 235mm Celestron EdgeHD SCT, CGEM Mount, Celestron Nightscape 10100 OSC CCD, LoadstarX2 guide camera, off axis guider.
The Deer Lick Group NGC7331 by Phill Froggett, Buckland, Hertfordshire, UK. Equipment: QHY8L, Skywatcher200p, NEQ6 (belt modified)
The Deer Lick Group NGC7331 by Phill Froggett, Buckland, Hertfordshire, UK. Equipment: QHY8L, Skywatcher200p, NEQ6 (belt modified)
Abell 1367, Quasars around NGC 3842 by Ryan Proctor, Wakefield, UK. Equipment: Nikond5500, Quattro 8s, Neq6, ZWO asi120mc-s Guider
Abell 1367, Quasars around NGC 3842 by Ryan Proctor, Wakefield, UK. Equipment: Nikond5500, Quattro 8s, Neq6, ZWO asi120mc-s Guider
Abell 1367 Galaxy Cluster by Ryan Proctor, Wakefield, UK. Equipment: Nikond5500, Quattro 8s, Neq6, ZWO asi120mc-s Guider
Abell 1367 Galaxy Cluster by Ryan Proctor, Wakefield, UK. Equipment: Nikond5500, Quattro 8s, Neq6, ZWO asi120mc-s Guider
Abell 2151 Galaxy Cluster by Mark Griffith, Swindon, Wiltshire, UK. Equipment: Teleskop service 12
Abell 2151 Galaxy Cluster by Mark Griffith, Swindon, Wiltshire, UK. Equipment: Teleskop service 12″ Richey-Chretien telescope, Skywatcher EQ8 mount, Atik 383L+ camera, Astronomik LRGB filters, Hutech IDAS light pollution filter.
NGC3190 Hickson 44 Galaxy Group by Mark Griffith, Swindon, Wiltshire, UK. Equipment: Teleskop service 12
NGC3190 Hickson 44 Galaxy Group by Mark Griffith, Swindon, Wiltshire, UK. Equipment: Teleskop service 12″ Richey-Chretien telescope, Skywatcher EQ8 mount, Atik 383L+ camera, Astronomik LRGB filters, Hutech IDAS light pollution filter.
Hickson 44 Galaxy Group by Mark Griffith, Swindon, Wiltshire, UK. Equipment: Teleskop service 12
Hickson 44 Galaxy Group by Mark Griffith, Swindon, Wiltshire, UK. Equipment: Teleskop service 12″ Richey-Chretien telescope, Skywatcher EQ8 mount, Atik 383L+ camera, Astronomik LRGB filters, Hutech IDAS light pollution filter, Astro physics 0.67 reducer.