What is Galaxy cluster: Definition and 18 Discussions

A galaxy cluster, or cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity with typical masses ranging from 1014–1015 solar masses. They are the largest known gravitationally bound structures in the universe and were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. One of the key features of clusters is the intracluster medium (ICM). The ICM consists of heated gas between the galaxies and has a peak temperature between 2–15 keV that is dependent on the total mass of the cluster. Galaxy clusters should not be confused with star clusters, such as galactic clusters—also known as open clusters—which are structures of stars within galaxies, or with globular clusters, which typically orbit galaxies. Small aggregates of galaxies are referred to as galaxy groups rather than clusters of galaxies. The galaxy groups and clusters can themselves cluster together to form superclusters.
Notable galaxy clusters in the relatively nearby Universe include the Virgo Cluster, Fornax Cluster, Hercules Cluster, and the Coma Cluster. A very large aggregation of galaxies known as the Great Attractor, dominated by the Norma Cluster, is massive enough to affect the local expansion of the Universe. Notable galaxy clusters in the distant, high-redshift Universe include SPT-CL J0546-5345 and SPT-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 as radio halos and radio relics. Using the Chandra X-ray Observatory, structures such as cold fronts and shock waves have also been found in many galaxy clusters.

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  1. S

    I More extended equilibrium configurations due to dark energy?

    Dark Energy puts a constrain on the size of overdensities (like clusters and superclusters of galaxies) and their growth. A higher Dark Energy density would reduce the radius of the zone where matter would be gravitationally bound, because more Dark Energy density would mean that objects would...
  2. S

    I Dark Energy contribution to plasma temperature in galaxy clusters?

    I have a question about this work called "Dark energy and key physical parameters of clusters of galaxies"*There, towards the end, the authors talk about the isothermal velocities and tempreature parameters of the gas and particles circulating between galaxies in clusters. In particular they...
  3. S

    I Expansion-Collapse cycle in cosmological structures?

    Concerning cosmological structures (like galaxies, clusters of galaxies, gas bodies, superclusters...etc) if the elements that make them are close enough they will be attracted towards each other by gravity. Contrarily, if they are sufficiently far apart they will get further away following the...
  4. S

    I Deviations of conservation laws in cosmological evolution?

    If energy is "not conserved" in General Relativity (or at least, it is difficult to define it) in the context of an expanding accelerating spacetime (like it happens in our Universe), are there any observations of deviations from the strict conservation laws in the evolution and formation of...
  5. S

    I Is energy conserved during the formation of local systems?

    I found an old article (https://journals.aps.org/pr/abstract/10.1103/PhysRev.137.B1379) which talks about conservation of energy in an expanding space. Apparently, the author found that energy is conserved at local scales (like the motion of planets in our solar system) as one would expect, but...
  6. T

    I What is a typical mass density for inter-galactic gas in a cluster?

    I assume we can work it out from X-ray emission detections, such as shown with the famous bullet cluster images.
  7. shahbaznihal

    A Galaxy statistics calculation in Saslaw's book

    I am trying to follow a calculation from the book of William C. Saslaw, The Distribution of the Galaxies: Gravitational Clustering in Cosmology. The calculation is shown on the pages following page 122 in chapter 14 where the author talks about the Correlation function. I am able to reproduce...
  8. F

    From the original burst, fraction of stellar mass still on the Main Sequence

    <Moderator's note: Moved from a technical forum and thus no template.> Suppose that all stars in this galaxy were born in a single major-merger burst event about 10 Gyr ago. From this original burst, I want to compute the fraction of stellar mass still surviving as stars in the main sequence ...
  9. R

    Mass of a Cluster of galaxies

    Homework Statement An estimate of the mass of the Coma cluster can be made from the velocity of the galaxies relative to the centre of mass of the cluster; the velocities are around 2000 km s-1. The stars that form the cluster have been together for a long time. Show that a simple model will...
  10. PrincePhoenix

    B Is the formation of galaxy groups explained correctly here?

    Hello! I watched a video on the Youtube channel Kurzgesagt titled How far can we go? Limits of humanity The video attempts to explain why we may be limited to our local galaxy group even with science fiction technologies. During a part of the video (starting at 2:26), they try to explain how...
  11. throneoo

    Average photon energy from a galaxy cluster

    Homework Statement I want to calculate/estimate the average photon energy from a galaxy cluster incident on the mirror of a X ray telescope (Chandra to be specific) . The cluster has redshift z and at constant uniform temperature T Homework Equations Specific Intensity of thermal...
  12. Earnest Guest

    Gas Mass Calcuation in Galaxy Cluster

    I found this: http://adsabs.harvard.edu/abs/1992A&A...259L..31B document that describes how the X-Ray emissions from galaxy clusters are used to calculate the mass of the cluster. I'm unable to follow the steps to calculating the gas mass. Specifically, in section (2) there is a formula for...
  13. Earnest Guest

    Do Galaxy Clusters follow De Vaucouleurs' Law?

    If objects in the universe are built hierarchically, wouldn't one expect a Galaxy Cluster that is roughly spherical to follow the same profile as an elliptical galaxy?
  14. P

    Astronomers find galaxy cluster with bursting heart

    Astronomers find galaxy cluster with bursting heart An international team of astronomers has discovered a gargantuan galaxy cluster with a core bursting with new stars - an incredibly rare find. The discovery, made with the help of the NASA/ESA Hubble Space Telescope, is the first to show that...
  15. Earnest Guest

    Improved MOND Model for Galaxy Cluster Kinematic Data

    I have a modification to MOND that appears to work much better than 'Standard' MOND at the galactic scale. I want to test this model now on larger structures. Does anyone know where I can find kinematic data on galaxy clusters, preferably some 'gold' standard that people have been examining for...
  16. synfiniti

    Are Galaxies in Hubble Telescope Photos of Clusters?

    Below are two URLs to Hubble telescope photos of galaxy clusters. I would like to know if every single white or colored splotch in these photos is a galaxy, or do single/individual stars/suns manage to get mixed in there? Thank you for your time...
  17. T

    Massive galaxy cluster could upend theory of universe evolut

    I saw this article and wondered if there is cause for concern? It does seem rather large and well defined so soon after the BB. Massive galaxy cluster could upend theory of universe evolution...
  18. M

    Galaxy cluster mass profiles

    I'm doing an undergraduate research project this term on some modified theories of gravity, and I need some mass/density profiles. Does anyone know any papers that give mass profiles of galaxy clusters determined predominantly through gravitational lensing measurements? The model I'm working...