Editing Galaxy rotation curve (section)

== Alternatives to dark matter ==

There have been a number of attempts to solve the problem of galaxy rotation by modifying gravity without invoking dark matter. One of the most discussed is [[modified Newtonian dynamics]] (MOND), originally proposed by [[Mordehai Milgrom]] in 1983, which modifies the Newtonian force law at low accelerations to enhance the effective gravitational attraction.<ref>{{Cite book |last=Merritt |first=D. |title=A Philosophical Approach to MOND: Assessing the Milgromian Research Program in Cosmology. |publisher=Cambridge University Press. |year=2020 |isbn=9781108665681}}</ref> MOND has had a considerable amount of success in predicting the rotation curves of low-surface-brightness galaxies,<ref>{{cite journal |author=S. S. McGaugh |author2=W. J. G. de Blok | title=Testing the Hypothesis of Modified Dynamics with Low Surface Brightness Galaxies and Other Evidence |journal=Astrophysical Journal | date=1998 | volume=499 | issue=1 | pages=66–81 | arxiv=astro-ph/9801102 | doi=10.1086/305629 | bibcode=1998ApJ...499...66M|s2cid=18901029 }}</ref> matching the [[baryonic Tully–Fisher relation]],<ref>{{cite journal | author=S. S. McGaugh | title=Novel Test of Modified Newtonian Dynamics with Gas Rich Galaxies | journal=Physical Review Letters | date=2011 | volume=106 | issue=12 | page=121303 | arxiv=1102.3913|doi=10.1103/PhysRevLett.106.121303|bibcode = 2011PhRvL.106l1303M | pmid=21517295| s2cid=1427896 }}</ref> and the velocity dispersions of the small satellite galaxies of the [[Local Group]].<ref>{{cite journal |author=S. S. McGaugh |author2=M. Milgrom | title=Andromeda Dwarfs in Light of Modified Newtonian Dynamics | date=2013 | volume=766 | issue=1 | page=22 | arxiv=1301.0822 |bibcode = 2013ApJ...766...22M |doi = 10.1088/0004-637X/766/1/22 | journal=The Astrophysical Journal|s2cid=118576979 }}</ref>

Using data from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database, a group has found that the radial acceleration traced by rotation curves (an effect given the name "radial acceleration relation") could be predicted just from the observed baryon distribution (that is, including stars and gas but not dark matter).<ref>{{cite journal |author=Stacy McGaugh |author2=Federico Lelli |author3=Jim Schombert | title=The Radial Acceleration Relation in Rotationally Supported Galaxies  | date=2016 | arxiv=1609.05917 | journal=Physical Review Letters |volume=117 |issue=20 |pages=201101 | doi = 10.1103/physrevlett.117.201101 |pmid=27886485 |bibcode=2016PhRvL.117t1101M |s2cid=34521243 }}</ref>  This so-called radial acceleration relation (RAR) might be fundamental for understanding the dynamics of galaxies.<ref>{{cite journal|doi=10.1093/mnras/stad2675|doi-access=free |title=On the fundamentality of the radial acceleration relation for late-type galaxy dynamics |date=2023 |last1=Stiskalek |first1=Richard |last2=Desmond |first2=Harry |journal=Monthly Notices of the Royal Astronomical Society |volume=525 |issue=4 |pages=6130–6145 |arxiv=2305.19978 }}</ref> The same relation provided a good fit for 2693 samples in 153 rotating galaxies, with diverse shapes, masses, sizes, and gas fractions. Brightness in the near infrared, where the more stable light from red giants dominates, was used to estimate the density contribution due to stars more consistently.  The results are consistent with MOND, and place limits on alternative explanations involving dark matter alone. However, cosmological simulations within a Lambda-CDM framework that include baryonic feedback effects reproduce the same relation, without the need to invoke new dynamics (such as MOND).<ref>{{cite journal|last1=Keller|first1=B. W.|last2=Wadsley|first2=J. W.|title=Λ is Consistent with SPARC Radial Acceleration Relation|journal=The Astrophysical Journal|date=23 January 2017|volume=835|issue=1|pages=L17|doi=10.3847/2041-8213/835/1/L17|bibcode=2017ApJ...835L..17K|arxiv = 1610.06183 |doi-access=free }}</ref> Thus, a contribution due to dark matter itself can be fully predictable from that of the baryons, once the feedback effects due to the dissipative collapse of baryons are taken into account.

Attempts to model of galaxy rotation based on a [[general relativity]] metric, showing that the rotation curves for the [[Milky Way]], [[Messier 81|NGC 3031]], [[NGC 3198]] and [[NGC 7331]] are consistent with the mass density distributions of the visible matter<ref>{{Cite journal|last1=Cooperstock|first1=F. I.|last2=Tieu|first2=S.|title=Galactic Dynamics Via General Relativity: A Compilation and New Developments |date=2007-05-20|url=https://www.worldscientific.com/doi/abs/10.1142/S0217751X0703666X|journal=International Journal of Modern Physics A|language=en|volume=22|issue=13|pages=2293–2325|doi=10.1142/S0217751X0703666X|issn=0217-751X|arxiv=astro-ph/0610370|bibcode=2007IJMPA..22.2293C |s2cid=155920 }}</ref> and other similar work<ref>{{Cite journal|last=Ludwig|first=G. O.|date=2021-02-23|title=Galactic rotation curve and dark matter according to gravitomagnetism|journal=The European Physical Journal C|language=|volume=81|issue=2|pages=186|doi=10.1140/epjc/s10052-021-08967-3|bibcode=2021EPJC...81..186L |issn=|doi-access=free}}</ref> have been disputed.<ref>{{Cite journal |last1=Lasenby |first1=A N |last2=Hobson |first2=M P |last3=Barker |first3=W E V |date=2023-10-09 |title=Gravitomagnetism and galaxy rotation curves: a cautionary tale |journal=Classical and Quantum Gravity |volume=40 |issue=21 |pages=215014 |doi=10.1088/1361-6382/acef8b |issn=0264-9381|arxiv=2303.06115 }}</ref>

According to recent analysis of the data produced by the [[Gaia (spacecraft)|Gaia spacecraft]], it would seem possible to explain at least the [[Milky Way]]'s rotation curve without requiring any dark matter if instead of a [[Newtonian approximation]] the entire set of equations of [[general relativity]] is adopted.<ref>{{cite journal
| last1 = Crosta
| first1 = Mariateresa
| last2 = Giammaria
| first2 = Marco
| last3 = Lattanzi
| first3 = Mario G.
| last4 = Poggio
| first4 = Eloisa
| date = August 2020
| title = On testing CDM and geometry-driven Milky Way rotation curve models with ''Gaia'' DR2 
| journal = [[Monthly Notices of the Royal Astronomical Society]]
| volume = 496
| issue = 2
| pages = 2107–2122
| doi = 10.1093/mnras/staa1511
| publisher = [[Oxford University Press|OUP]]
| doi-access = free
| arxiv = 1810.04445
}}</ref><ref>{{cite journal
| last1 = Beordo
| first1 = William
| last2 = Crosta
| first2 = Mariateresa
| last3 = Lattanzi
| first3 = Mario G.
| last4 = Re Fiorentin
| first4 = Paola
| last5 = Spagna
| first5 = Alessandro
| date = April 2024
| title = Geometry-driven and dark-matter-sustained Milky Way rotation curves with ''Gaia'' DR3 
| journal = [[Monthly Notices of the Royal Astronomical Society]]
| volume = 529
| issue = 4
| pages = 4681–4698
| doi = 10.1093/mnras/stae855
| publisher = [[Oxford University Press|OUP]]
| doi-access = free
}}</ref>