Editing Cuspy halo problem

{{short description|Unsolved problem in physics}}
The '''cuspy halo problem''' (also known as the '''core-cusp problem''') is a discrepancy between the inferred [[dark matter]] density profiles of low-mass galaxies and the density profiles predicted by cosmological [[N-body simulation]]s. Nearly all simulations form dark matter halos which have "cuspy" dark matter distributions, with density increasing steeply at small radii, while the rotation curves of most observed dwarf galaxies suggest that they have flat central dark matter density profiles ("cores").<ref>{{cite journal|last1=Moore|first1=Ben|title=Evidence against dissipation-less dark matter from observations of galaxy haloes|journal=Nature|date=August 1994|volume=370|issue=6491|pages=629–631|doi=10.1038/370629a0|display-authors=etal|bibcode = 1994Natur.370..629M |s2cid=4325561}}</ref><ref>{{cite journal|last1=Oh|first1=Se-Heon|title=High-resolution Mass Models of Dwarf Galaxies from LITTLE THINGS|journal=The Astronomical Journal|date=May 2015|volume=149|issue=6|pages=180|display-authors=etal|arxiv=1502.01281|bibcode = 2015AJ....149..180O |doi = 10.1088/0004-6256/149/6/180 |s2cid=1389457}}</ref>

Several possible solutions to the core-cusp problem have been proposed. Many recent studies have shown that including [[baryonic]] feedback (particularly feedback from [[supernova]]e and [[Active galactic nucleus|active galactic nuclei]]) can "flatten out" the core of a galaxy's dark matter profile, since feedback-driven gas outflows produce a time-varying [[gravitational potential]] that transfers energy to the orbits of the collisionless dark matter particles.<ref>{{cite journal|last1=Navarro|first1=Julio|title=The cores of dwarf galaxy haloes|journal=MNRAS|date=December 1996|volume=283|issue=3|pages=L72–L78|doi=10.1093/mnras/283.3.l72|doi-access=free |display-authors=etal|arxiv = astro-ph/9610187 |bibcode = 1996MNRAS.283L..72N }}</ref><ref>{{cite journal|last1=Pontzen|first1=Andrew|title=How supernova feedback turns dark matter cusps into cores|journal=Nature|date=2012|volume=421|issue=4|pages=3464–3471|doi=10.1111/j.1365-2966.2012.20571.x|doi-access=free |display-authors=etal|arxiv = 1106.0499 |bibcode = 2012MNRAS.421.3464P |s2cid=26992856}}</ref> Other works have shown that the core-cusp problem can be solved outside of the most widely accepted Cold Dark Matter (CDM) paradigm: simulations with [[Warm dark matter|warm]] or [[Self-interacting dark matter|self-interacting]] dark matter also produce dark matter cores in low-mass galaxies.<ref>{{cite journal|last1=Lovell|first1=Mark|title=The haloes of bright satellite galaxies in a warm dark matter universe|journal=MNRAS|date=March 2012|volume=420|issue=3|pages=2318–2324|doi=10.1111/j.1365-2966.2011.20200.x|doi-access=free |display-authors=etal|arxiv = 1104.2929 |bibcode = 2012MNRAS.420.2318L |s2cid=53698295}}</ref><ref>{{cite journal|last1=Elbert|first1=Oliver|title=Core formation in dwarf haloes with self-interacting dark matter: no fine-tuning necessary|journal=MNRAS|date=October 2015|volume=453|issue=1|pages=29–37|doi=10.1093/mnras/stv1470|doi-access=free |display-authors=etal|arxiv = 1412.1477 |bibcode = 2015MNRAS.453...29E }}</ref> It is also possible that the distribution of dark matter that minimizes the system energy has a flat central dark matter density profile.<ref name=":0">{{Cite journal|last=Runstedtler|first=Allan|date=November 2018|title=A model for the mass and distribution of particles in dark matter halos|journal=Canadian Journal of Physics|volume=96|issue=11|pages=1178–1182|doi=10.1139/cjp-2017-0804|issn=0008-4204|bibcode=2018CaJPh..96.1178R|s2cid=125555275 }}</ref>

==Simulation results==

According to W.J.G. de Blok "The presence of a cusp in the centers of CDM halos is one of the earliest and strongest results derived from N-body cosmological simulations."<ref>{{cite journal|author1=de Blok |author2=W. J. G. |title=The core-cusp problem|year=2009|arxiv=0910.3538|bibcode = 2010AdAst2010E...5D |doi = 10.1155/2010/789293 |volume=2010 |journal=Advances in Astronomy |pages=1–14|s2cid=55026264 |doi-access=free }}</ref> Numerical simulations for CDM structure formation predict some structure properties that conflict with astronomical observations.

==Observations==

The discrepancies range from galaxies to clusters of galaxies. "The main one that has attracted a lot of attention is the cuspy halo problem, namely that CDM models predict halos that have a high density core or have an inner profile that is too steep compared to observations."<ref>{{cite journal|author=Hui, L.|title=Unitarity Bounds and the Cuspy Halo Problem|journal=Phys. Rev. Lett.|year=2001|volume=86|issue=16|pages=3467–3470|arxiv=astro-ph/0102349|bibcode = 2001PhRvL..86.3467H |doi = 10.1103/PhysRevLett.86.3467|pmid=11328000|s2cid=22259958}}</ref>

==Potential solutions==

The conflict between numerical simulations and [[astronomical observation]]s creates numerical constraints related to the core/cusp problem. Observational constraints on halo concentrations imply the existence of theoretical constraints on cosmological parameters. According to [[Stacy McGaugh|McGaugh]], Barker, and de Blok,<ref>{{cite journal|author1=McGaugh, S.S. |author2=Barker, M.K. |author3=de Blok, W.J.G. |title=A limit on the cosmological mass density and power spectrum from the rotation curves of low surface brightness galaxies|journal=The Astrophysical Journal|date=Feb 20, 2003|volume=584|issue=2 |pages=566–576|arxiv = astro-ph/0210641 |bibcode = 2003ApJ...584..566M |doi = 10.1086/345806 |s2cid=14888119 }}</ref> there might be 3 basic possibilities for interpreting the halo concentration limits stated by them or anyone else:
#"CDM halos must have cusps, so the stated limits hold and provide new constraints on cosmological parameters."<ref>{{cite journal|author1=Valenzuela, O. |author2=Rhee, G. |author3=Klypin, A. |author4=Governato, F.,Stinson, G. |author5=Quinn, T.|author5-link=Tom Quinn (astrophysicist) |author6=Wadsley, J. |title=Is There Evidence for Flat Cores in the Halos of Dwarf Galaxies? The Case of NGC 3109 and NGC 6822|journal=The Astrophysical Journal|date=Feb 20, 2007|volume=657|issue=2 |pages=773–789|arxiv = astro-ph/0509644 |bibcode = 2007ApJ...657..773V|doi = 10.1086/508674 |s2cid=14206466 }}</ref>
#"Something (e.g. feedback, modifications of the nature of dark matter) eliminates cusps and thus the constraints on cosmology."<ref>{{cite journal|author1=Governato, F. |author2=Brook, C. |author3=Mayer, L. |author4=Brooks, A.,Rhee, G. |author5=Jonsson, P. |author6=Willman, B. |author7=Stinson, G. |author8=Quinn, T. |author9=Madau, P. |title=Bulgeless dwarf galaxies and dark matter cores from supernova-driven outflows|journal=Nature|date=Jan 20, 2010|volume=463|issue=7278 |pages=203–206|arxiv = 0911.2237 |bibcode = 2010Natur.463..203G|doi = 10.1038/nature08640 |pmid=20075915|s2cid=4411280 }}</ref>
# "The picture of halo formation suggested by CDM simulations is wrong."

One approach to solving the cusp-core problem in galactic halos is to consider models that modify the nature of dark matter; theorists have considered [[Warm dark matter|warm]], [[fuzzy cold dark matter|fuzzy]], [[Self-interacting dark matter|self-interacting]], and [[meta-cold dark matter|meta-]]cold dark matter, among other possibilities.<ref>{{cite journal|author1=McGaugh, S.S. |author2=de Blok, W.J.G. |author3=Schombert, J.M. |author4=Kuzio de Naray, R. |author5=Kim, J.H. |title=The rotation velocity attributable to dark matter at intermediate radii in disk galaxies|journal=The Astrophysical Journal|volume=659|issue=1 |date=April 10, 2007|pages=149–161|arxiv = astro-ph/0612410 |bibcode = 2007ApJ...659..149M |doi = 10.1086/511807 |s2cid=15193438 }}</ref> One straightforward solution could be that the distribution of dark matter that minimizes the system energy has a flat central dark matter density profile.<ref name=":0" />

==See also==
* [[Dwarf galaxy problem]] (also known as "the missing satellites problem")
* [[List of unsolved problems in physics]]

==References==
{{reflist}}

{{Dark matter}}

[[Category:Dark matter]]
[[Category:Unsolved problems in physics]]