We study the structure of compact objects that contain non-self annihilating, self-interacting dark matter admixed with ordinary matter made of neutron star and white dwarf materials. We extend the ...previous work Phys. Rev. D 92, 123002 (2015) on these dark compact objects by analyzing the effect of weak and strongly interacting dark matter with particle masses in the range of 1–500 GeV, so as to set some constraints in the strength of the interaction and the mass of the dark matter particle. We find that the total mass of the compact objects increases with decreasing dark matter particle mass. In the strong interacting case and for dark matter particle masses in the range 1–10 GeV, the total mass of the compact objects largely exceeds the 2 M ⊙ constraint for neutron star masses and the nominal 1 M ⊙ for white dwarfs, while for larger dark matter particle masses or in the weakly interacting case the compact objects show masses in agreement or smaller than these constraints, thus hinting at the exclusion of strongly self-interacting dark matter of masses 1–10 GeV in the interior of these compact objects. Moreover, we observe that the smaller the dark matter particle mass, the larger the quantity of dark matter captured is, putting constraints on the dark matter mass trapped in the compact objects so as to fulfill ≃ 2 M ⊙ observations. Finally, the inhomogeneity of distribution of dark matter in the Galaxy implies a mass dependence of compact objects from the environment which can be used to put constraints on the characteristics of the Galaxy halo DM profile and on particle mass. In view of these results, we discuss the formation of the dark compact objects in an homogeneous and nonhomogeneous dark matter environment.
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Neutron star mass in dark matter clumps Deliyergiyev, Maksym; Del Popolo, Antonino; Le Delliou, Morgan
Monthly Notices of the Royal Astronomical Society,
11/2023, Volume:
527, Issue:
3
Journal Article
Peer reviewed
Open access
ABSTRACT
This paper investigates a hypothesis proposed in previous research relating neutron star (NS) mass and its dark matter (DM) accumulation. As DM accumulates, NS mass decreases, predicting ...lower NS masses toward the Galactic centre. Due to limited NSs data near the Galactic centre, we examine NSs located within DM clumps. Using the CLUMPY code simulations, we determine the DM clumps distribution, with masses from 10 to 108 M⊙ and scales from 10−3 to 10 kpc. These clumps’ DM exhibit a peak at the centre, tapering toward the outskirts, resembling our Galaxy’s DM distribution. We analyse these DM clumps’ NS mass variations, considering diverse DM particle masses and galaxy types. We find relatively stable NS mass within 0.01 – 5 kpc from the clump centre. This stability supports the initial hypothesis, particularly for NSs located beyond 0.01 kpc from the clump centre, where NS mass reaches a plateau around 0.1 kpc. Nevertheless, NS mass near the clump’s periphery reveals spatial dependence: NS position within DM clumps influences its mass in Milky Way-type galaxies. Moreover, this dependence varies with the DM model considered. In summary, our study investigates the proposed link between NS mass and DM accumulation by examining NSs within DM clumps. While NS mass remains stable at certain distances from the clump centre, spatial dependencies arise near the clump’s outer regions, contingent on the specific DM model.
This review aims at proposing to the field an overview of the Cusp-core problem, including a discussion of its advocated solutions, assessing how each can satisfactorily provide a description of ...central densities. Whether the Cusp-core problem reflects our insufficient grasp on the nature of dark matter, of gravity, on the impact of baryonic interactions with dark matter at those scales, as included in semi-analytical models or fully numerical codes, the solutions to it can point either to the need for a paradigm change in cosmology, or to to our lack of success in ironing out the finer details of the ΛCDM paradigm.
The ΛCDM model, or concordance cosmology, as it is often called, is a paradigm at its maturity. It is clearly able to describe the universe at large scale, even if some issues remain open, such as ...the cosmological constant problem, the small-scale problems in galaxy formation, or the unexplained anomalies in the CMB. ΛCDM clearly shows difficulty at small scales, which could be related to our scant understanding, from the nature of dark matter to that of gravity; or to the role of baryon physics, which is not well understood and implemented in simulation codes or in semi-analytic models. At this stage, it is of fundamental importance to understand whether the problems encountered by the ΛDCM model are a sign of its limits or a sign of our failures in getting the finer details right. In the present paper, we will review the small-scale problems of the ΛCDM model, and we will discuss the proposed solutions and to what extent they are able to give us a theory accurately describing the phenomena in the complete range of scale of the observed universe.
An Anisotropic Model for the Universe Delliou, Morgan Le; Deliyergiyev, Maksym; del Popolo, Antonino
Symmetry,
10/2020, Volume:
12, Issue:
10
Journal Article
Peer reviewed
Open access
Motivated by the back-reaction debate, and some unexplained characteristics of the CMB, we investigate the possibility of some anisotropy in the universe observed around us. To this aim, we build up ...a novel prediction for the Hubble law for the late universe from a Bianchi type I model, taken as proof of concept, transcribing the departure of such model from a ΛCDM model. We dicussed the redshift measurement in this universe, and finally formalized the Hubble diagram.
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In principle, the local cosmic void can be simply modeled by the spherically symmetric Lemaitre–Tolman–Bondi (LTB) metric. In practice, the real local cosmic void is probably not spherically ...symmetric. In this paper, to reconstruct a more realistic profile of the local cosmic void, we divide it into several segments. Each segment with certain solid angle is modeled by its own LTB metric. Meanwhile, we divide the 1048 type Ia supernovae (SNIa) of the Pantheon Survey into corresponding subsets according to their distribution in the galactic coordinate system. Obviously, each SNIa subset can only be used to reconstruct the profile of one segment. Finally, we can patch together an irregular profile for the local cosmic void with the whole Pantheon sample. Note that, the paucity of each data subset lead us to focus on the inner part of each void segment and assume that the half radii of the void segments are sufficient to constrain the whole segment. We find that, despite
2
σ
signals of anisotropy limited to the depth of the void segments, the constraints on every void segment are consistent with
Λ
CDM model at 95% CL. Moreover, our constraints are too weak to challenge the cosmic homogeneity and isotropy.
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The Birkhoff theorem is a well-known result in general relativity, and it is used in many applications. However, its most general version, due to Bona, is almost unknown and presented in a form less ...accessible to the relativist and cosmologist community. Moreover, many wield it mistakenly as a simple transposition of Newton’s iron sphere theorem. In the present work, we propose a modern, dual null, presentation-useful in many explorations, including black holes-of the theorem that renders accessible most of the results of Bona’s version. In addition, we discuss the fluid contents admissible for the application of the theorem, beyond a vacuum, and we demonstrate how the formalism greatly simplifies solving the dynamical equations and allows one to express the solution as a power expansion in r. We present a family of solutions that share the properties predicted by the Birkhoff theorem and discuss the existence of trapped and antitrapped regions. The formalism manifestly shows how the type of region-trapped or untrapped-determines the character of the Killing vector.
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In this paper, we extend the work of Freundlich et al. 2020 who showed how to obtain a Dekel–Zhao density profile with mass dependent shape parameters in the case of galaxies. In the case of ...Freundlich et al. 2020, the baryonic dependence was obtained using the NIHAO set of simulations. In our case, we used simulations based on a model of ours. Following Freundlich et al. 2020, we obtained the dependence from baryon physics of the two shape parameters, obtaining in this way a mass dependent Dekel–Zhao profile describing the dark matter profiles from galaxies to clusters of galaxies. The extension to the Dekel–Zhao mass dependent profile to clusters of galaxies is the main result of the paper. In the paper, we show how the Dekel–Zhao mass dependent profile gives a good description of the density profiles of galaxies, already shown by Freundlich et al. 2020, but also to a set of clusters of galaxies.
Neutron Stars and Dark Matter Del Popolo, Antonino; Le Delliou, Morgan; Deliyergiyev, Maksym
Universe,
12/2020, Volume:
6, Issue:
12
Journal Article
Peer reviewed
Open access
Neutron stars change their structure with accumulation of dark matter. We study how their mass is influenced from the environment. Close to the sun, the dark matter accretion from the neutron star ...does not have any effect on it. Moving towards the galactic center, the density increase in dark matter results in increased accretion. At distances of some fraction of a parsec, the neutron star acquire enough dark matter to have its structure changed. We show that the neutron star mass decreases going towards the galactic centre, and that dark matter accumulation beyond a critical value collapses the neutron star into a black hole. Calculations cover cases varying the dark matter particle mass, self-interaction strength, and ratio between the pressure of dark matter and ordinary matter. This allow us to constrain the interaction cross section, σdm, between nucleons and dark matter particles, as well as the dark matter self-interaction cross section.
In this paper, we extend a paper by Milgrom (2009, MNRAS 398, 1023) dealing with the existence of a quasi-universal surface density for object of all mass and structure, if they are in the Newtonian ...regime, i.e., that their mean acceleration is larger than MOND typical acceleration a0. This result is in agreement with Donato et al. (2009)’s results, claiming the existence of a quasi-universal surface density in all masses in galaxies. The Milgrom paper also predicts that objects with mean inner acceleration smaller than the values discussed do not show the quasi-universal behavior of the surface density discussed. In the present paper, we extend the result of Milgrom’s paper, based on a point mass model, considering spiral galaxies, modelled with a double exponential disk. Similar to Milgrom’s results, we find the existence of a universal surface density for galaxies with large surface density, and a different behavior for galaxies having small surface density.
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