Models of dark matter halos based on statistical mechanics: The fermionic King model

Chavanis, Pierre‐Henri; Lemou, Mohammed; Méhats, Florian

doi:10.1103/physrevd.92.123527

Cited by 69 publications

(215 citation statements)

References 136 publications

(358 reference statements)

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“…The solution to this system of equations leads to a continuous and novel dense corediluted halo DM profile from the center all the way to the galactic halo (see Siutsou et al 2015;Argüelles et al 2016;Mavromatos et al 2017, for its applications). Similar core-halo profiles with applications to fermionic DM were also obtained in Bilic et al (2002) and more recently in Chavanis et al (2015) from a statistical approach within Newtonian gravity.…”

Section: Ruffini-argüelles-rueda Model Of Dark Mattersupporting

confidence: 73%

Geodesic motion of S2 and G2 as a test of the fermionic dark matter nature of our Galactic core

Becerra-Vergara

Argüelles

Krut

et al. 2020

A&A

116

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The motion of S-stars around the Galactic center implies that the central gravitational potential is dominated by a compact source, Sagittarius A* (Sgr A*), which has a mass of about 4 × 106 M⊙ and is traditionally assumed to be a massive black hole (BH). The explanation of the multiyear accurate astrometric data of the S2 star around Sgr A*, including the relativistic redshift that has recently been verified, is particularly important for this hypothesis and for any alternative model. Another relevant object is G2, whose most recent observational data challenge the scenario of a massive BH: its post-pericenter radial velocity is lower than expected from a Keplerian orbit around the putative massive BH. This scenario has traditionally been reconciled by introducing a drag force on G2 by an accretion flow. As an alternative to the central BH scenario, we here demonstrate that the observed motion of both S2 and G2 is explained in terms of the dense core – diluted halo fermionic dark matter (DM) profile, obtained from the fully relativistic Ruffini-Argüelles-Rueda (RAR) model. It has previously been shown that for fermion masses 48−345 keV, the RAR-DM profile accurately fits the rotation curves of the Milky Way halo. We here show that the solely gravitational potential of such a DM profile for a fermion mass of 56 keV explains (1) all the available time-dependent data of the position (orbit) and line-of-sight radial velocity (redshift function z) of S2, (2) the combination of the special and general relativistic redshift measured for S2, (3) the currently available data on the orbit and z of G2, and (4) its post-pericenter passage deceleration without introducing a drag force. For both objects, we find that the RAR model fits the data better than the BH scenario: the mean of reduced chi-squares of the time-dependent orbit and z data are ⟨χ̄2⟩S2,RAR ≈ 3.1 and ⟨χ̄2⟩S2,BH ≈ 3.3 for S2 and ⟨χ̄2⟩G2,RAR ≈ 20 and ⟨χ̄2⟩G2,BH ≈ 41 for G2. The fit of the corresponding z data shows that while for S2 we find comparable fits, that is, χ̄2z,RAR ≈ 1.28 and χ̄2z,BH ≈ 1.04, for G2 the RAR model alone can produce an excellent fit of the data, that is, χ̄2z,RAR ≈ 1.0 and χ̄2z,BH ≈ 26. In addition, the critical mass for gravitational collapse of a degenerate 56 keV-fermion DM core into a BH is ∼ 108 M⊙. This result may provide the initial seed for the formation of the observed central supermassive BH in active galaxies, such as M 87.

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Section: Ruffini-argüelles-rueda Model Of Dark Mattersupporting

confidence: 73%

Geodesic motion of S2 and G2 as a test of the fermionic dark matter nature of our Galactic core

Becerra-Vergara

Argüelles

Krut

et al. 2020

A&A

116

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“…For WDM, this is not true: its maximal phase-space density f max is finite at early times and does not increase during halo formation [17]. Usually, density distri-butions with finite f max are derived either from analytical studies of self-gravitating Fermi-Dirac dark matter (see, e.g., [18][19][20][21][22][23][24][25][26][27]) or from N -body simulations imitating initial dark matter velocities (see, e.g., [28][29][30][31][32]).…”

Section: Pacsmentioning

confidence: 99%

New Model of Density Distribution for Fermionic Dark Matter Halos

Rudakovskyi

Savchenko

2018

Ukr. J. Phys.

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PACSIn this paper, we formulate a new model of density distribution for halos made of warm dark matter (WDM) particles. The model is described by a single microphysics parameter the mass (or, equivalently, the maximal value of the initial phase-space density distribution) of dark matter particles. Given the WDM particle mass and the parameters of a dark matter density profile at the halo periphery, this model predicts the inner density profile. In case of initial Fermi-Dirac distribution, we successfully reproduce cored dark matter profiles from N -body simulations. Also, we calculate the core radii of warm dark matter halos of dwarf spheroidal galaxies for particle masses mfd = 100, 200, 300 and 400 eV. K e y w o r d s: Dark matter: warm, cold; dark matter halo profile; cores; Navarro-Frenk-White profileThe nature of dark matter the largest gravitating substance in the Universe is not yet identified. Usual (left-handed) neutrinos the only natural dark matter candidate within the Standard Model of particle physics are too light to form the observed large-scale structure of the Universe [1] and the densest dark matter-dominated objects, dwarf spheroidals (dSphs) [2]. So far, many extensions of the Standard Model containing a viable dark matter candidate have been proposed; see, e.g., reviews [3][4][5][6]. In terms of their initial velocities, valid dark matter candidates can be split in two groups 1 (see, e.g., [9]):• cold dark matter (CDM), composed of particles with small (non-relativistic) initial velocities [10,11]; c A.V. RUDAKOVSKYI, D.O. SAVCHENKO, 2018 1 Note that, for some specific dark matter particle candidates, their initial velocity spectrum can be approximated by a mixture of 'cold ' and 'warm' components [7, 8].• warm dark matter (WDM), composed of particles with large (relativistic) initial velocities [12,13].Density distribution of CDM haloes is often described by the Navarro-Frenk-White (NFW) profile [14,15] ρ nfw (r) = ρ s r s r 1 + r rs 2 . (1) Its parameters ρ s and r s are connected with the halo mass M 200 (the mass within the sphere of radius R 200 , within which the average density is 200 times larger than the critical density ρ crit of the Universe) and halo concentration parameter c 200 = R 200 /r s .The phase-space density for CDM haloes becomes infinite towards the halo centre; see, e.g., [16]. For WDM, this is not true: its maximal phase-space density f max is finite at early times and does not increase during halo formation [17]. Usually, density distri-

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“…In Lynden-Bell's theory, further developed by Chavanis and Sommeria [88], the quasistationary state generically has a core-halo structure with a completely degenerate core at T = 0 (effective fermion ball) 7 The halo cannot be exactly isothermal otherwise it would have an infinite mass [7]. In reality, the density in the halo decreases as r −3 , similarly to the NFW [27] and Burkert [28] profiles, or even as r −4 (see Appendix D of [89] and Appendix I of [90]), instead of r −2 corresponding to the isothermal sphere [7]. This extra-confinement may be due to incomplete relaxation, tidal effects, and stochastic perturbations as discussed in Appendix B of [79].…”

Section: Introductionmentioning

confidence: 96%

Predictive model of BEC dark matter halos with a solitonic core and an isothermal atmosphere

Chavanis

2019

Phys. Rev. D

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121

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We develop a model of Bose-Einstein condensate dark matter halos with a solitonic core and an isothermal atmosphere based on a generalized Gross-Pitaevskii-Poisson equation [P.H. Chavanis, Eur. Phys. J. Plus 132, 248 (2017)]. This equation provides a heuristic coarse-grained parametrization of the ordinary Gross-Pitaevskii-Poisson equation accounting for violent relaxation and gravitational cooling. It involves a cubic nonlinearity taking into account the self-interaction of the bosons, a logarithmic nonlinearity associated with an effective temperature, and a source of dissipation. It leads to superfluid dark matter halos with a core-halo structure. The quantum potential or the self-interaction of the bosons generates a solitonic core that solves the cusp problem of the cold dark matter model. The logarithmic nonlinearity generates an isothermal atmosphere accounting for the flat rotation curves of the galaxies. The dissipation ensures that the system relaxes towards an equilibrium configuration. In the Thomas-Fermi approximation, the dark matter halo is equivalent to a barotropic gas with an equation of state P = 2πas 2 ρ 2 /m 3 + ρkBT /m, where as is the scattering length of the bosons and m is their individual mass. We numerically solve the equation of hydrostatic equilibrium and determine the corresponding density profiles and rotation curves. We impose that the surface density of the halos has the universal value Σ0 = ρ0r h = 141 M /pc 2 obtained from the observations. For a boson with ratio as/m 3 = 3.28 × 10 3 fm/(eV/c 2 ) 3 , we find a minimum halo mass (M h )min = 1.86 × 10 8 M and a minimum halo radius (r h )min = 788 pc. This ultracompact halo corresponds to a pure soliton which is the ground state of the Gross-Pitaevskii-Poisson equation. For (M h )min < M h < (M h ) * = 3.30 × 10 9 M the soliton is surrounded by a tenuous isothermal atmosphere without plateau. For M h > (M h ) * we find two branches of solutions corresponding to (i) pure isothermal halos without soliton and (ii) isothermal halos harboring a central soliton and presenting a plateau. The purely isothermal halos (gaseous phase) are stable. For M h > (M h )c = 6.86 × 10 10 M , they are indistinguishable from the observational Burkert profile. For (M h ) * < M h < (M h )c, the deviation from the isothermal law (most probable state) may be explained by incomplete violent relaxation, tidal effects, or stochastic forcing. The isothermal halos harboring a central soliton (core-halo phase) are canonically unstable (having a negative specific heat) but they are microcanonically stable so they are long-lived. By extremizing the free energy (or entropy) with respect to the core mass, we find that the core mass scales as Mc/(M h )min = 0.626 (M h /(M h )min) 1/2 ln(M h /(M h )min). For a halo of mass M h = 10 12 M , similar to the mass of the halo that surrounds our Galaxy, the solitonic core has a mass Mc = 6.39×10 10 M and a radius Rc = 1 kpc. The solitonic core cannot mimic by itself a supermassive black hole at the center of the Galaxy but i...

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Models of dark matter halos based on statistical mechanics: The fermionic King model

Cited by 69 publications

References 136 publications

Geodesic motion of S2 and G2 as a test of the fermionic dark matter nature of our Galactic core

Geodesic motion of S2 and G2 as a test of the fermionic dark matter nature of our Galactic core

New Model of Density Distribution for Fermionic Dark Matter Halos

Predictive model of BEC dark matter halos with a solitonic core and an isothermal atmosphere

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