Editing Dwarf spheroidal galaxy (section)

== Evidence of dark matter ==
Because of the faintness of the lowest-luminosity dwarf spheroidal galaxies and the nature of the stars contained within them, some astronomers suggest that dwarf spheroidal galaxies and [[Globular cluster|globular clusters]] may not be clearly separate and distinct types of objects.<ref name="Bergh20074">{{cite journal |last=van den Bergh |first=Sidney |author-link=Sidney van den Bergh |date=November 2007 |title=Globular clusters and dwarf spheroidal galaxies |journal= Monthly Notices of the Royal Astronomical Society: Letters |volume=385 |issue=1 |pages=L20–L22 |doi=10.1111/j.1745-3933.2008.00424.x |doi-access=free |bibcode=2008MNRAS.385L..20V |arxiv=0711.4795|s2cid=15093329 }}</ref> Other recent studies, however, have found a distinction in that the total amount of mass inferred from the motions of stars in dwarf spheroidals is many times that which can be accounted for by the mass of the stars themselves. Studies reveal that dwarf spheroidal galaxies have a dynamical mass of around 10{{sup|7}}&nbsp;{{solar mass}}, which is very large despite the low luminosity of dSph galaxies.<ref name=":23"/>

Although at fainter luminosities of dwarf spheroidal galaxies, it is not universally agreed upon how to differentiate between a dwarf spheroidal galaxy and a star cluster; however, many astronomers decide this depending on the object's dynamics: If it seems to have more [[dark matter]], then it is likely that it is a dwarf spheroidal galaxy rather than an enormous, faint [[star cluster]]. In the current predominantly accepted [[Lambda-CDM model|Lambda cold dark matter]] cosmological model, the presence of dark matter is often cited as a reason to classify dwarf spheroidal galaxies as a different class of object from [[globular cluster]]s, which show little to no signs of dark matter. Because of the extremely large amounts of dark matter in dwarf spheroidal galaxies, they may deserve the title "most dark matter-dominated galaxies."<ref name="Strigari20074">{{cite journal |last1=Strigari |first1=Louie |first2=Savvas M. |last2=Koushiappas |last3=Bullock |first3=James S. |last4=Kaplinghat |first4=Manoj |last5=Simon |first5=Joshua D. |last6=Geha |first6=Marla|author6-link= Marla Geha |last7=Willman |first7=Beth |display-authors=etal |year=2008 |title=The most dark matter dominated galaxies: Predicted gamma-ray signals from the faintest Milky Way dwarfs |journal=The Astrophysical Journal |volume=678 |issue=2 |pages=614–620 |arxiv=0709.1510 |bibcode=2008ApJ...678..614S |doi=10.1086/529488|s2cid=11415491 }}</ref>

Further evidence of the prevalence of dark matter in dSphs includes  the case of Fornax dwarf spheroidal galaxy, which can be assumed to be in dynamic equilibrium to estimate mass and amount of dark matter, since the gravitational effects of the Milky Way are small.<ref name=":33">{{cite journal |last1=Battaglia |first1=Giuseppina |last2=Sollima |first2=Antonio |last3=Nipoti |first3=Carlo |year=2015 |title=The effect of tides on the Fornax dwarf spheroidal galaxy |journal=Monthly Notices of the Royal Astronomical Society |volume=454 |issue=3 |pages=2401–2415 |arxiv = 1509.02368 |bibcode = 2015MNRAS.454.2401B |doi = 10.1093/mnras/stv2096 |doi-access=free }}</ref> Unlike the Fornax galaxy, there is evidence that the UMa2, a dwarf spheroidal galaxy in the [[Ursa Major|Ursa Major constellation]], experiences strong tidal disturbances from the Milky Way.<ref name=":13"/>

A topic of research is how much the internal dynamics of dwarf spheroidal galaxies are affected by the gravitational tidal dynamics of the galaxy they are orbiting. In other words, dwarf spheroidal galaxies could be prevented from achieving equilibrium due to the gravitational field of the Milky Way or other galaxy that they orbit.<ref name=":03"/> For example, the [[Sextans Dwarf Spheroidal|Sextans dwarf spheroidal galaxy]] has a velocity dispersion of 7.9±1.3&nbsp;km/s, which is a velocity dispersion that could not be explained solely by its stellar mass according to the [[Virial theorem|Virial Theorem]]. Similar to Sextans, previous studies of [[Hercules (dwarf galaxy)|Hercules dwarf spheroidal galaxy]] reveal that its orbital path does not correspond to the mass contained in Hercules.<ref>{{Cite journal |last1=Roderick |first1=T.A. |last2=Jerjen |first2=H. |last3=Da Costa |first3=G.S. |last4=Mackey |first4=A.D. |year=2016 |title=Structural analysis of the Sextans dwarf spheroidal galaxy |journal=Monthly Notices of the Royal Astronomical Society |volume=460 |issue=1 |pages=30–43 |arxiv = 1604.06214 |bibcode = 2016MNRAS.460...30R |doi = 10.1093/mnras/stw949 |doi-access=free }}</ref> Furthermore, there is evidence that the UMa2, a dwarf spheroidal galaxy in the [[Ursa Major|Ursa Major constellation]], experiences strong tidal disturbances from the Milky Way.<ref name=":13"/>