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Galaxy cluster

From Wikipedia, the free encyclopedia
Structure made up of a gravitationally-bound aggregation of hundreds of galaxies
Composite image of five galaxies clustered together just 600 million years after the Universe's birth[1]

Agalaxy cluster, or acluster of galaxies, is a structure that consists of anywhere from hundreds to thousands ofgalaxies that are bound together bygravity,[1] with typical masses ranging from 1014 to 1015solar masses. Clusters consist of galaxies, heated gas, and dark matter.[2] They are the second-largest knowngravitationally bound structures in theuniverse aftersuperclusters. They were believed to be thelargest known structures in the universe until the 1980s, whensuperclusters were discovered.[3] Small aggregates of galaxies are referred to asgalaxy groups rather than clusters of galaxies. Together,galaxy groups and clusters form superclusters.

Basic properties

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Galaxy clusterIDCS J1426 is located 10 billion light-years from Earth and has the mass of almost 500 trillion suns (multi-wavelength image: X-rays in blue, visible light in green, and infrared light in red).[4]

Galaxy clusters typically have the following properties:

  • They contain 100 to 1,000 galaxies, hotX-ray emitting gas and large amounts ofdark matter.[2] Details are described in the "Composition" section.
  • They have total masses of 1014 to 1015solar masses.
  • They typically have diameters from 1 to 5Mpc (see1023 m for distance comparisons).
  • The spread of velocities for the individual galaxies is about 800–1000 km/s.

Composition

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Galaxy clusters have three main components. Galaxies themselves only make up a small fraction of clusters, although they are the only component we can detect in thevisible spectrum. The heated gas of the intracluster medium (ICM) has a peak temperature between 30 and 100 million degrees Celsius.[2] Dark matter makes up the majority of the mass of galaxy clusters, but cannot be detected optically.[3]

ComponentMass fractionDescription
Galaxies1%In optical observations, only galaxies are visible
Intergalactic gas inintracluster medium9%Plasma between the galaxies at high temperature and emit x-ray radiation by thermalbremsstrahlung
Dark matter90%Most massive component but cannot be detected optically and is inferred through gravitational interactions

Cluster formation and evolution

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As galaxy clusters form, massive amounts of energy are released due to shock waves, the heating of gas, and galaxy interactions.[3] Gas collides with existing material which generates shock waves, heating it to tens of millions of degrees and producing X-ray emissions. Galaxy evolution within the cluster is governed by interactions between galaxies, such asgalaxy mergers, and gas stripping.

Classification

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There are many classification systems for galaxy clusters, based on characteristics such as shape symmetry, X-rayluminosity, and dominant galaxy type.[5] TheBautz-Morgan classification sorts clusters into types I, II, and III based on the relative brightness of their galaxies–type I with greatest contrast and type III with the least.[6][7]

Galaxy clusters as measuring instruments

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Gravitational redshift

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Galaxy clusters have been used by Radek Wojtak from the Niels Bohr Institute at the University of Copenhagen to test predictions ofgeneral relativity: energy loss from light escaping a gravitational field. Photons emitted from the center of a galaxy cluster should lose more energy than photons coming from the edge of the cluster because gravity is stronger in the center. Light emitted from the center of a cluster has a longer wavelength than light coming from the edge. This effect is known asgravitational redshift. Using the data collected from 8000 galaxy clusters, Wojtak was able to study the properties of gravitational redshift for the distribution of galaxies in clusters. He found that the light from the clusters was redshifted in proportion to the distance from the center of the cluster as predicted by general relativity. The result also strongly supports theLambda-Cold Dark Matter model of the Universe, according to which most of the cosmos is made up ofDark Matter that does not interact with matter.[8]

Gravitational lensing

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Galaxy clusters are also used for their strong gravitational potential asgravitational lenses to boost the reach of telescopes.[9] The gravitational distortion of space-time occurs near massive galaxy clusters and bends the path of photons to create a cosmic magnifying glass. This can be done with photons of any wavelength from the optical to the X-ray band. The latter is more difficult, because galaxy clusters emit a lot of X-rays.[10] However, X-ray emission may still be detected when combining X-ray data to optical data. One particular case is the use of the Phoenix galaxy cluster to observe a dwarf galaxy in its early high energy stages of star formation.[11]

Notable galaxy clusters

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TheLaniakea supercluster with manygalaxy clusters
Main article:List of galaxy groups and clusters

Notable galaxy clusters in the relatively nearby universe include theVirgo Cluster,Fornax Cluster,Hercules Cluster, and theComa Cluster. A very large aggregation of galaxies known as theGreat Attractor, dominated by theNorma Cluster, is massive enough to affect thelocal expansion of the Universe. Notable galaxy clusters in the distant, high-redshift universe includeSPT-CL J0546-5345 andSPT-CL J2106-5844, the most massive galaxy clusters found in the early Universe. In the last few decades, they are also found to be relevant sites of particle acceleration, a feature that has been discovered by observing non-thermal diffuse radio emissions, such asradio halos andradio relics. Using theChandra X-ray Observatory, structures such as cold fronts andshock waves have also been found in many galaxy clusters.

ClusterNotes
Virgo ClusterThe nearest massive galaxy cluster
Norma ClusterThe cluster at the heart of theGreat Attractor
Bullet ClusterA cluster merger with the first observed separation between dark matter and normal matter
This lists some of the most notable clusters; for more clusters, see the list article.

Gallery

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Left: Image by theHubble Space Telescope (2017) Right: Image by theJames Webb Space Telescope (2022)[12]
Abell 2744 galaxy cluster – extremely distantgalaxies revealed bygravitational lensing (16 October 2014).[19][20]

Images

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Videos

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  • Video: Formation of galaxy clusterMRC 1138-262 (artist's concept).

See also

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Wikimedia Commons has media related toGalaxy clusters.

References

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  1. ^ab"Hubble Pinpoints Furthest Protocluster of Galaxies Ever Seen".ESA/Hubble Press Release. Retrieved13 January 2015.
  2. ^abc"Groups & Clusters of Galaxies".Chandra X-ray Observatory.
  3. ^abcKravtsov, A. V.; Borgani, S. (2012). "Formation of Galaxy Clusters".Annual Review of Astronomy and Astrophysics.50:353–409.arXiv:1205.5556.Bibcode:2012ARA&A..50..353K.doi:10.1146/annurev-astro-081811-125502.S2CID 119115331.
  4. ^"Galaxy cluster IDCS J1426". Retrieved11 January 2016.
  5. ^"Clusters and Superclusters of Galaxies".ned.ipac.caltech.edu. Retrieved2025-02-17.
  6. ^Bautz, L. P.; Morgan, W. W. (1970-12-01)."On the Classification of the Forms of Clusters of Galaxies".The Astrophysical Journal.162: L149.doi:10.1086/180643.ISSN 0004-637X.
  7. ^"1978ApJ...222...23D Page 23".adsabs.harvard.edu. Retrieved2025-02-17.
  8. ^Yudhijit, Bhattacharjee."Galaxy Clusters Back Up Einstein's Theory of Relativity".Wired. Retrieved2022-04-04.
  9. ^Walker, Stephen; Simionescu, Aurora; Nagai, Daisuke; Okabe, Nobuhiro; Eckert, Dominique; Mroczkowski, Tony; Akamatsu, Hiroki; Ettori, Stefano; Ghirardini, Vittorio (2019-01-02)."The Physics of Galaxy Cluster Outskirts".Space Science Reviews.215 (1): 7.arXiv:1810.00890.doi:10.1007/s11214-018-0572-8.ISSN 1572-9672.
  10. ^Reiprich, Thomas H.; Basu, Kaustuv; Ettori, Stefano; Israel, Holger; Lovisari, Lorenzo; Molendi, Silvano; Pointecouteau, Etienne; Roncarelli, Mauro (2013-08-01)."Outskirts of Galaxy Clusters".Space Science Reviews.177 (1):195–245.arXiv:1303.3286.doi:10.1007/s11214-013-9983-8.ISSN 1572-9672.
  11. ^Chu, Jennifer (15 October 2019)."Astronomers use giant galaxy cluster as X-ray magnifying lens".MIT News. Retrieved2022-04-04.
  12. ^Chow, Denise; Wu, Jiachuan (12 July 2022)."Photos: How pictures from the Webb telescope compare to Hubble's - NASA's $10 billion telescope peers deeper into space than ever, revealing previously undetectable details in the cosmos".NBC News. Retrieved16 July 2022.
  13. ^Garner, Rob (11 July 2022)."NASA's Webb Delivers Deepest Infrared Image of Universe Yet".NASA.Archived from the original on 12 July 2022. Retrieved12 July 2022.
  14. ^Overbye, Dennis; Chang, Kenneth; Tankersley, Jim (11 July 2022)."Biden and NASA Share First Webb Space Telescope Image – From the White House on Monday, humanity got its first glimpse of what the observatory in space has been seeing: a cluster of early galaxies".The New York Times.Archived from the original on 12 July 2022. Retrieved12 July 2022.
  15. ^Pacucci, Fabio (15 July 2022)."How Taking Pictures of 'Nothing' Changed Astronomy - Deep-field images of "empty" regions of the sky from Webb and other space telescopes are revealing more of the universe than we ever thought possible".Scientific American. Retrieved16 July 2022.
  16. ^Deliso, Meredith; Longo, Meredith; Rothenberg, Nicolas (14 July 2022)."Hubble vs. James Webb telescope images: See the difference".ABC News. Retrieved15 July 2022.
  17. ^Kooser, Amanda (13 July 2012)."Hubble and James Webb Space Telescope Images Compared: See the Difference - The James Webb Space Telescope builds on Hubble's legacy with stunning new views of the cosmos".CNET. Retrieved16 July 2022.
  18. ^Atkinson, Nancy (2 May 2022)."Now, We can Finally Compare Webb to Other Infrared Observatories".Universe Today.Archived from the original on 10 May 2022. Retrieved12 May 2022.
  19. ^abClavin, Whitney; Jenkins, Ann; Villard, Ray (7 January 2014)."NASA's Hubble and Spitzer Team up to Probe Faraway Galaxies".NASA. Retrieved8 January 2014.
  20. ^Chou, Felecia; Weaver, Donna (16 October 2014)."RELEASE 14-283 – NASA's Hubble Finds Extremely Distant Galaxy through Cosmic Magnifying Glass".NASA. Retrieved17 October 2014.
  21. ^"Distant and ancient".www.spacetelescope.org. Retrieved6 May 2019.
  22. ^"Strings of homeless stars".www.spacetelescope.org. Retrieved11 June 2018.
  23. ^"From toddlers to babies".www.spacetelescope.org. Retrieved7 May 2018.
  24. ^"Approaching the Universe's origins".www.spacetelescope.org. Retrieved16 April 2018.
  25. ^"HAWK-I and Hubble Explore a Cluster with the Mass of two Quadrillion Suns".www.eso.org. Retrieved25 December 2017.
  26. ^"Streaks and stripes".www.spacetelescope.org. Retrieved27 November 2017.
  27. ^"Cosmic RELICS".www.spacetelescope.org. Retrieved6 November 2017.
  28. ^"Cosmic archaeology".www.spacetelescope.org. Retrieved24 October 2017.
  29. ^"Hubble pushed beyond limits to spot clumps of new stars in distant galaxy".www.spacetelescope.org. Retrieved12 July 2017.
  30. ^Loff, Sarah; Dunbar, Brian (10 February 2015)."Hubble Sees A Smiling Lens".NASA. Retrieved10 February 2015.
  31. ^"Image of the galaxy cluster SpARCS1049". Retrieved11 September 2015.
  32. ^"Magnifying the distant Universe".ESA/Hubble Picture of the Week. Retrieved10 April 2014.
  33. ^"Seeing Triple". October 18, 2023.
Morphology
Structure
Active nuclei
Energetic galaxies
Low activity
Interaction
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