Editing Elliptical galaxy

{{Short description|Spherical or ovoid mass of stars}}
{{More footnotes needed|date=March 2015}}
{{Use dmy dates|date=October 2019}}

[[Image:Abell S740, cropped to ESO 325-G004.jpg|thumb|The giant elliptical galaxy [[ESO 325-4]]]]

An '''elliptical galaxy''' is a type of [[galaxy]] with an approximately [[ellipsoid]]al shape and a smooth, nearly featureless image. They are one of the three main [[galaxy morphological classification|classes of galaxy]] described by [[Edwin Hubble]] in his [[Hubble sequence#Physical significance|Hubble sequence]] and 1936 work ''The Realm of the Nebulae'',<ref name=Hubble-1936>{{cite book |last=Hubble |first=E.P. |author-link=Edwin Hubble |title=The realm of the nebulae |year=1936 |publisher=[[Yale University Press]] |location=New Haven |isbn=9780300025002 |oclc=611263346 |series=Mrs. Hepsa Ely [[Silliman Memorial Lectures]], 25 |url=https://books.google.com/books?id=kgiXdDGLpFUC }} [https://archive.org/details/TheRealmOfTheNebulae Alt URL](pp.&nbsp;124–151)</ref> along with [[spiral galaxy|spiral]] and [[lenticular galaxy|lenticular]] galaxies. 
Elliptical (E) galaxies are, together with lenticular galaxies (S0) with their large-scale disks, and ES galaxies<ref name="adsabs.harvard.edu">Liller, M.H. (1966), [http://adsabs.harvard.edu/abs/1966ApJ...146...28L The Distribution of Intensity in Elliptical Galaxies of the Virgo Cluster. II]</ref><ref>Nieto, J.-L. et al. (1988), [http://adsabs.harvard.edu/abs/1988A%26A...195L...1N More isotropic oblate rotators in elliptical galaxies]</ref><ref>Graham, A.W. et al. (2016), [http://adsabs.harvard.edu/abs/2016ApJ...831..132G Disky Elliptical Galaxies and the Allegedly Over-massive Black Hole in the Compact “ES“ Galaxy NGC 1271 (see their Fig.7).]</ref> with their intermediate scale disks, a subset of the "early-type" galaxy population.

Most elliptical galaxies are composed of older, [[stellar evolution#Low-mass stars|low-mass stars]], with a sparse [[interstellar medium]], and they tend to be surrounded by large numbers of [[globular cluster]]s. [[Star formation]] activity in elliptical galaxies is typically minimal; they may, however, undergo brief periods of star formation when merging with other galaxies.<ref>{{cite journal |last1=Pearson |first1=W. J. |last2=Wang |first2=L. |last3=Alpaslan |first3=M. |last4=Baldry |first4=I. |last5=Bilicki |first5=M. |last6=Brown |first6=M. J. I. |last7=Grootes |first7=M. W. |last8=Holwerda |first8=B. W. |last9=Kitching |first9=T. D. |last10=Kruk |first10=S. |last11=van der Tak |first11=F. F. S. |title=Effect of galaxy mergers on star-formation rates |journal=Astronomy & Astrophysics |date=November 2019 |volume=631 |pages=A51 |doi=10.1051/0004-6361/201936337|arxiv=1908.10115 |bibcode=2019A&A...631A..51P }}</ref> Elliptical galaxies are believed to make up approximately 10–15% of galaxies in the [[Virgo Supercluster]], and they are not the dominant type of galaxy in the universe overall.<ref>{{cite journal|author=Loveday, J.|date=February 1996|title=The APM Bright Galaxy Catalogue.|journal=[[Monthly Notices of the Royal Astronomical Society]]|volume=278|issue=4|pages=1025–1048|arxiv=astro-ph/9603040|bibcode=1996MNRAS.278.1025L|doi=10.1093/mnras/278.4.1025|doi-access=free }}</ref> They are preferentially found close to the centers of [[galaxy cluster]]s.<ref>{{cite journal|author=Dressler, A.|date=March 1980|title=Galaxy morphology in rich clusters – Implications for the formation and evolution of galaxies.|journal=The Astrophysical Journal|volume=236|pages=351–365|bibcode=1980ApJ...236..351D|doi=10.1086/157753|doi-access=free}}</ref>

Elliptical galaxies range in size from dwarf ellipticals with tens of millions of stars, to [[Type-cD galaxy|supergiants]] of over one hundred trillion [[star]]s that dominate their galaxy clusters. Originally, Edwin Hubble hypothesized that elliptical galaxies evolved into spiral galaxies, which was later discovered to be false,<ref name="author">John, D. (2006). ''Astronomy: The definitive guide to the universe''. Bath, UK: Parragon Publishing., p. 224-225</ref> although the accretion of gas and smaller galaxies may build a disk around a pre-existing ellipsoidal structure.<ref>Dekel, A., et al. (2009), [http://adsabs.harvard.edu/abs/2009Natur.457..451D Cold streams in early massive hot haloes as the main mode of galaxy formation]</ref><ref>Stewart, Kyle R., et al. (2013), [http://adsabs.harvard.edu/abs/2013ApJ...769...74S Angular Momentum Acquisition in Galaxy Halos]</ref>
Stars found inside of elliptical galaxies are on average much older than stars found in spiral galaxies.<ref name="author" />

==Examples==
*[[3C 244.1]]
*[[Messier 49|M49 (NGC 4472)]]
*[[Messier 59|M59 (NGC 4621)]]
*[[Messier 60|M60 (NGC 4649)]]
*[[Messier 87|M87 (NGC 4486)]], whose supermassive black hole was the first black hole to be imaged by the [[Event Horizon Telescope]].<ref name=BHImage>{{cite journal |author=The Event Horizon Telescope Collaboration |year=2019 |title=First M87 Event Horizon Telescope results. IV. Imaging the central supermassive black hole |journal=The Astrophysical Journal |volume=875 |issue=1 |page=L4 |issn=2041-8213 |doi=10.3847/2041-8213/ab0e85 |arxiv=1906.11241 |bibcode=2019ApJ...875L...4E |s2cid=146068771 |url=https://repository.ubn.ru.nl/bitstream/2066/202543/1/202543.pdf |doi-access=free }}</ref><ref name=EHT2019>{{cite magazine |author=Jeffrey, K. |date=10 April 2019 |title=These are the first pictures of a black hole — And that's a big, even supermassive, deal |magazine=[[Time (magazine)|Time]] |url=https://time.com/5566225/first-black-hole-picture-photo/ |access-date=10 April 2019}}</ref>
*[[Messier 89|M89 (NGC 4552)]]
*[[Messier 105|M105 (NGC 3379)]]
*[[NGC 4697]], part of the [[NGC 4697 Group]]
*[[ESO 383-76]], one of the [[List of largest galaxies|largest galaxies known]].
*[[IC 1101]], the central galaxy of [[Abell 2029]]
*[[Hercules A]], supergiant elliptical galaxy
*[[Maffei 1]], the closest giant elliptical galaxy
*[[CGCG 049-033]], known for having the longest galactic jet discovered
*[[Centaurus A|Centaurus A (NGC 5128)]], an elliptical/lenticular [[radio galaxy]] with peculiar morphology and unusual dust lanes
*[[NeVe 1]], the source of the [[Ophiuchus Supercluster]] eruption, the most powerful astronomical event known
*[[Messier 86|M86]]  ([[Messier 86|4406]]) an elliptical or [[lenticular galaxy]] in the [[constellation]] [[Virgo (constellation)|Virgo]]

== General characteristics ==
[[File:Elliptical galaxy IC 2006.jpg|thumb|Elliptical galaxy [[IC 2006]]<ref>{{cite web|title=Elliptical galaxy IC 2006|url=http://www.spacetelescope.org/images/heic1508a/|website=www.spacetelescope.org|publisher=ESA/Hubble|access-date=21 April 2015}}</ref>]]

Elliptical galaxies are characterized by several properties that make them distinct from other classes of galaxy. They are spherical or ovoid masses of stars, starved of star-making gases. Furthermore, there is very little [[interstellar matter]] (neither gas nor dust), which results in low rates of [[star formation]], few [[Open cluster|open star clusters]], and few young stars; rather elliptical galaxies are dominated by [[Population II|old stellar populations]], giving them red colors. Large elliptical galaxies typically have an extensive system of [[globular cluster]]s. They generally have two distinct populations of globular clusters: one that is redder and metal-rich, and another that is bluer and metal-poor.<ref>{{cite journal|doi=10.3847/1538-3881/ac680d|title=The Ancient Globular Clusters of NGC 1291 |year=2022 |last1=Hixenbaugh |first1=Kyle |last2=Chandar |first2=Rupali |last3=Mok |first3=Angus |journal=The Astronomical Journal |volume=163 |issue=6 |page=271 |s2cid=248853311 |arxiv=2205.14047 | bibcode=2022AJ....163..271H |doi-access=free }}</ref>
[[File:Galactic fireflies.jpg|thumb|The galaxy located in the image is [[4C 73.08]], a giant elliptical galaxy.<ref>{{Cite web |last=information@eso.org |title=Galactic fireflies |url=https://esahubble.org/images/potw1246a/ |access-date=2024-09-12 |website=www.esahubble.org |language=en}}</ref>]]
The dynamical properties of elliptical galaxies and the [[Bulge (astronomy)|bulges]] of [[Disc galaxy|disk galaxies]] are similar, suggesting that they may be formed by the same physical processes, although this remains controversial. The [[Luminosity#In astronomy|luminosity]] profiles of both elliptical galaxies and bulges are well fit by [[Sersic profile|Sersic's law]], and a range of scaling relations between the elliptical galaxies' structural parameters unify the population.<ref>Graham, A.W. (2013), [http://adsabs.harvard.edu/abs/2013pss6.book...91G Elliptical and Disk Galaxy Structure and Modern Scaling Laws]</ref>

Every massive elliptical galaxy contains a [[supermassive black hole]] at its center. Observations of 46 elliptical galaxies, 20 classical bulges, and 22 pseudobulges show that each contain a black hole at the center.<ref>{{Cite journal|last1=Kormendy|first1=John|last2=Ho|first2=Luis C.|date=18 August 2013|title=Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies|journal=Annual Review of Astronomy and Astrophysics|volume=51|issue=1|pages=511–653|doi=10.1146/annurev-astro-082708-101811|issn=0066-4146|arxiv = 1304.7762 |bibcode = 2013ARA&A..51..511K |s2cid=118172025}}</ref> The mass of the black hole is tightly correlated with the mass of the galaxy,<ref>Graham, A.W. (2016), [http://adsabs.harvard.edu/abs/2016ASSL..418..263G Galaxy Bulges and Their Massive Black Holes: A Review]</ref> evidenced through correlations such as the [[M–sigma relation]] which relates the [[velocity dispersion]] of the surrounding stars to the mass of the black hole at the center.

Elliptical galaxies are preferentially found in [[galaxy clusters]] and in compact [[Galaxy group|groups of galaxies]].

Unlike flat [[spiral galaxy|spiral galaxies]] with organization and structure, elliptical galaxies are more three-dimensional, without much structure, and their stars are in somewhat random orbits around the center.

==Sizes and shapes==
[[File:A Multi-Wavelength View of Radio Galaxy Hercules A.jpg|thumb|[[Hercules A]], a supergiant elliptical galaxy and also a [[radio galaxy]]. The radio lobes shown here in pink are over a million light-years across.]]
The [[List of largest galaxies|largest galaxies]] are supergiant ellipticals, or [[Type-cD galaxy|type-cD galaxies]]. Elliptical galaxies vary greatly in both size and mass with diameters ranging from 3,000 [[light year]]s to more than 700,000 light years, and masses from 10<sup>5</sup> to nearly 10<sup>13</sup> solar masses.<ref>{{cite book|last1=Fraknoi|first1=Andrew|last2=Morrison|first2=David|last3=Wolf|first3=Sidney C.|title=Open Stax Astronomy|date=13 January 2017|url=https://cnx.org/contents/LnN76Opl@10.13:1G3DS4T6@3/Properties-of-Galaxies|access-date=2 February 2017}}</ref> This range is much broader for this galaxy type than for any other. The smallest, the [[Dwarf elliptical galaxy|dwarf elliptical galaxies]], may be no larger than a typical [[globular cluster]], but contain a considerable amount of [[dark matter]] not present in clusters. Most of these small galaxies may not be related to other ellipticals.[[File:MACSJ1423.8+2404.jpg|thumb|The brilliant central object is the supergiant elliptical galaxy SDSS J142347.87+240442.4, the dominant member of the [[galaxy cluster]] MACS J1423.8+2404. It has a diameter of 380,000 light-years.<ref name=NED_SDSSJ1423>{{Cite web|url=https://ned.ipac.caltech.edu/cgi-bin/objsearch?objname=SDSS+J142347.87+240442.4&extend=no&hconst=67.74&omegam=0.3089&omegav=0.6911&corr_z=1&out_csys=Equatorial&out_equinox=J2000.0&obj_sort=RA+or+Longitude&of=pre_text&zv_breaker=30000.0&list_limit=5&img_stamp=YES|title=Your NED Search Results|website=ned.ipac.caltech.edu|accessdate=8 May 2023}}</ref> Note the [[gravitational lensing]].]]

The [[Galaxy morphological classification|Hubble classification]] of elliptical galaxies contains an integer that describes how elongated the galaxy image is.
The classification is determined by the ratio of the major (''a'') to the minor (''b'') axes of the galaxy's [[Contour line#Other phenomena|isophotes]]:

:<math>10 \times \left(1 - \frac{b}{a}\right)</math>

Thus for a spherical galaxy with ''a'' equal to ''b'', the number
is 0, and the Hubble type is E0. While the limit in the literature is about E7, it has been known since 1966<ref name="adsabs.harvard.edu" /> that the E4 to E7 galaxies are misclassified lenticular galaxies with disks inclined at different angles to our line of sight. This has been confirmed through spectral observations revealing the rotation of their stellar disks.<ref>Graham, A.W. et al. (1998), [http://adsabs.harvard.edu/abs/1998A%26AS..133..325G Extended stellar kinematics of elliptical galaxies in the Fornax cluster]</ref><ref>Emsellem, E. (2011), [http://adsabs.harvard.edu/abs/2011MNRAS.414..888E The ATLAS<sup>3D</sup> project – III. A census of the stellar angular momentum within the effective radius of early-type galaxies: unveiling the distribution of fast and slow rotators]</ref> Hubble recognized that his shape classification depends both on the intrinsic shape of the galaxy, as well as the angle with which the galaxy is observed. Hence, some galaxies with Hubble type E0 are actually elongated.

It is sometimes said that there are two physical types of ellipticals: the giant ellipticals with slightly "boxy"-shaped isophotes, whose shapes result from random motion which is greater in some directions than in others (anisotropic random motion); and the "disky" normal and [[dwarf elliptical]]s, which contain disks.<ref>Pedraz, S. et al. (2002), [http://adsabs.harvard.edu/abs/2002MNRAS.332L..59P Evidence of fast rotation in dwarf elliptical galaxies]</ref><ref>Toloba, E. et al. (2015), [http://adsabs.harvard.edu/abs/2015ApJ...799..172T Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-type Galaxies from the SMAKCED Project. III. Angular Momentum and Constraints on Formation Scenarios]</ref> This is, however, an abuse of the nomenclature, as there are two types of early-type galaxy, those with disks and those without. Given the existence of ES galaxies with intermediate-scale disks, it is reasonable to expect that there is a continuity from E to ES, and onto the S0 galaxies with their large-scale stellar disks that dominate the light at large radii.

[[Dwarf spheroidal galaxy|Dwarf spheroidal galaxies]] appear to be a distinct class: their properties are more similar to those of irregulars and late spiral-type galaxies.

At the large end of the elliptical spectrum, there is further division, beyond Hubble's classification. Beyond ''gE'' giant ellipticals, lies [[Type-D galaxy|D-galaxies]] and [[Type-cD galaxy|cD-galaxies]]. These are similar to their smaller brethren, but more diffuse, with large haloes that may as much belong to the galaxy cluster within which they reside than the centrally-located giant galaxy.

[[File:A galactic mega-merger.jpg|thumb|[[NGC 3597]] is the product of a collision between two galaxies. It is evolving into a giant elliptical galaxy.]]

==Star formation==
In recent years, evidence has shown that a reasonable proportion (~25%) of early-type (E, ES and S0) galaxies have residual gas reservoirs<ref name="Young2011">{{cite journal|author=Young, L. M.|display-authors=etal|date=June 2011|title=The Atlas3D project – IV: the molecular gas content of early-type galaxies|journal=Monthly Notices of the Royal Astronomical Society|volume=414|issue=2|pages=940–967|arxiv=1102.4633|bibcode=2011MNRAS.414..940Y|doi=10.1111/j.1365-2966.2011.18561.x|doi-access=free |s2cid=119267988}}</ref>
and low-level star formation.<ref name="Crocker2011">{{cite journal|last=Crocker|first=A. F.|display-authors=etal|date=January 2011|title=Molecular gas and star formation in early-type galaxies|journal=Monthly Notices of the Royal Astronomical Society|volume=410|issue=2|pages=1197–1222|arxiv=1007.4147|bibcode=2011MNRAS.410.1197C|doi=10.1111/j.1365-2966.2010.17537.x|doi-access=free |s2cid=54764264}}</ref>

[[Herschel Space Observatory]] researchers have speculated that the central black holes in elliptical galaxies keep the gas from cooling enough for star formation.<ref>{{Cite web|url=http://www.hngn.com/articles/25442/20140227/red-and-dead-galaxies-have-beating-black-hole-hearts-preventing-star-formation.htm|title=Red And Dead Galaxies Have Beating Black Hole 'Hearts', Preventing Star Formation &#124; HNGN - Headlines & Global News|date=27 February 2014 |accessdate=8 May 2023}}</ref>

==See also==
* [[Firehose instability]]
* [[Fundamental plane (elliptical galaxies)]]
* [[Galaxy color–magnitude diagram]]
* [[Galaxy morphological classification]]
* [[Hubble sequence]]
* [[Lenticular galaxy]]
* [[Osipkov–Merritt model]]
* [[Sersic profile]]

==References==
{{reflist|30em}}

==Further reading==
* {{Citation |last1=Mo |first1= Houjun|last2=van den Bosch|first2=Frank|last3=White|first3=Simon|title=Galaxy Formation and Evolution |publisher= [[Cambridge University Press]] |date=June 2010   |edition=1 |isbn= 978-0521857932 }}

==External links==
{{Commons category|Elliptical galaxies}}
*[http://messier.seds.org/elli.html Elliptical Galaxies], SEDS Messier pages
*[http://csep10.phys.utk.edu/astr162/lect/galaxies/elliptical.html Elliptical Galaxies] ([https://web.archive.org/web/20130412000638/http://csep10.phys.utk.edu/astr162/lect/galaxies/elliptical.html Archived])

{{Galaxy}}

[[Category:Elliptical galaxies| ]]
[[Category:Galaxy morphological types]]