We study the hydrostatic equilibrium configuration of an admixture of degenerate dark matter and normal nuclear matter by using a general relativistic two-fluid formalism. We consider non- self-annihilating dark matter particles of mass ~ 1 GeV. The mass-radius relations and moments of inertia of these dark-matter admixed neutron stars are investigated and the stability of these stars is demonstrated by performing a radial perturbation analysis. We find a new class of compact stars which consists of a small normal matter core with radius of a few km embedded in a ten-kilometer- sized dark matter halo. These stellar objects may be observed as extraordinarily small neutron stars that are incompatible with realistic nuclear matter models.
In [Leung et al., Phys. Rev. D 84, 107301 (2011)], we presented our results on using a general relativistic two-fluid formalism to study the hydrostatic equilibrium configuration of an admixture of degenerate dark matter and normal nuclear matter. In this work, we present more analysis to complement our previous findings. We study the radial oscillation modes of these compact stars in detail. We find that these stars in general have two classes of oscillation modes. For a given total mass of the star, the first class of modes is insensitive to the dark-matter particle mass. They also reduce pr…
Scalar and vector dark matter admixed neutron stars with linear and quadratic couplings
Università di Salerno（萨莱诺大学）；INFN, Gruppo collegato di Salerno（意大利国家核物理研究所萨莱诺协作组）；Institute for Particle Physics Phenomenology (IPPP), Department of Physics, Durham University（达勒姆大学粒子物理现象学研究所）
We study the equilibrium structures of white dwarfs with dark matter cores formed by non-self-annihilating dark matter DM particles with mass ranging from 1 GeV to 100 GeV, which are assumed to form an ideal degenerate Fermi gas inside the stars. For DM particles of mass 10 GeV and 100 GeV, we find that stable stellar models exist only if the mass of the DM core inside the star is less than O(10^-3) Msun and O(10^-6) Msun, respectively. The global properties of these stars, and in particular the corresponding Chandrasekhar mass limits, are essentially the same as those of traditional white dwa…
We study the structural properties like the gravitational mass, radius and tidal deformability of dark matter (DM) admixed strange quark stars (SQSs). For the purpose we consider the vector MIT Bag model to describe the strange quark matter (SQM) and investigate the possible presence of accreted DM in the SQSs consequently forming DM admixed SQSs. We introduce feeble interaction between SQM and the accreted fermionic DM via a vector dark boson mediator. Considering the present literature, in the context of possible presence of DM in SQSs, this work is the first to consider interaction between …
Observational bounds on Dark Matter Admixed Neutron Stars from Gravitational Wave Data
Instituto Nacional de Pesquisas Espaciais（巴西国家空间研究所）；Universidade Federal do Rio Grande do Sul（南里奥格兰德联邦大学）；Universidade Federal do Espírito Santo（圣埃斯皮里图联邦大学）
We perform two-dimensional hydrodynamic simulations for the thermonuclear explosion of Chandrasekhar-mass white dwarfs with dark matter (DM) cores in Newtonian gravity. We include a 19-isotope nuclear reaction network and make use of the pure turbulent deflagration model as the explosion mechanism in our simulations. Our numerical results show that the general properties of the explosion depend quite sensitively on the mass of the DM core M$_{\rm DM}$: a larger M$_{\rm DM}$ generally leads to a weaker explosion and a lower mass of synthesized iron-peaked elements. In particular, the total mass…
We present simulations of thermonuclear supernovae admixed with an extended component of fermionic cold dark matter. We consider the explosion of a Chandrasekhar-mass white dwarf using the deflagration model with deflagration-detonation transition with spherical symmetry. The dark matter component is comparable in size with that of the normal matter, and so the system is described by two-fluid, one-dimensional Eulerian hydrodynamics. The explosion leaves all the dark matter trapped as a remnant compact dark star in all of our considered models. The presence of dark matter lengthens the deflagr…
The distribution of the dark matter (DM) in DM-admixed-neutron stars (DANSs) is supposed to be either a dense dark core or an extended dark halo, which is subject to the DM fraction of DANS ($f_χ$) and the DM properties, such as the mass ($m_χ$) and the strength of the self-interaction ($y$). In this paper, we perform an in-depth analysis of the formation criterion for dark core/dark halo and point out that the relative distribution of these two components is essentially determined by the ratio of the central enthalpy of the DM component to that of the baryonic matter component inside DANSs. F…
We investigate the possible presence of dark matter (DM) in massive and rotating neutron stars (NSs). For the purpose we extend our previous work [1] to introduce a light new physics vector mediator besides a scalar one in order to ensure feeble interaction between fermionic DM and $β$ stable hadronic matter in NSs. The masses of DM fermion, the mediators and the couplings are chosen consistent with the self-interaction constraint from Bullet cluster and from present day relic abundance. Assuming that both the scalar and vector mediators contribute equally to the relic abundance, we compute th…
We study the gravitational effect of non-self-annihilating dark matter on compact stellar objects. The self-interaction of condensate dark matter can give high accretion rate of dark matter onto stars. Phase transition to condensation state takes place when the dark matter density exceeds the critical value. A compact degenerate dark matter core is developed and alter the structure and stability of the stellar objects. Condensate dark matter admixed neutron stars is studied through the two-fuid TOV equation. The existence of condensate dark matter deforms the mass-radius relation of neutron st…
Evolution of Neutron Star Environment in the Galactic Halo : Implications for Dark Matter Accretion
Dharampeth M. P. Deo Memorial Science College（Dharampeth M. P. Deo 纪念科学学院）；BITS-Pilani Hyderabad Campus（比拉尼理工学院海德拉巴校区）；Inter-University Centre for Astronomy and Astrophysics（大学间天文学与天体物理中心）；Universidad de Salamanca（萨拉曼卡大学）
In the present paper we study the oscillation spectrum of neutron stars containing both ordinary matter and dark energy in different proportions. Within the model we consider, the equilibrium configurations are numerically constructed and the results show that the properties of the mixed neuron-dark-energy star can differ significantly when the amount of dark energy in the stars is varied. The oscillations of the mixed neuron-dark-energy stars are studied in the Cowling approximation. As a result we find that the frequencies of the fundamental mode and the higher overtones are strongly affecte…
It is by now well established that non-relativistic matter in the Universe is dominated by dark matter, the origin and nature of which still remains a mystery. Although the collisionless dark matter paradigm works very well at large distances, a few puzzles at galactic scales arise. These problems may be tackled assuming a self-interacting dark matter. If dark matter is accumulated inside a star it will modify its evolution and its properties, such as mass-to-radius profiles and frequency oscillation modes. Asteroseismology is a relatively new, powerful tool that allows us to constrain dark ma…
We study the density distribution of the minimally-coupled scalar field dark energy inside a neutron star. The dark energy is considered in the hydrodynamical representation as a perfect fluid with three parameters (background density, equation of state, and effective sound speed). The neutron star matter is modeled with three unified equations of state, developed by the Brussels-Montreal group. With the calculated density distribution of the dark energy inside a neutron star (and its dependence on the dark energy parameters) we investigate how its presence impacts the macroscopic characterist…
Motivated by the recent detection of the gravitational wave signal emitted by a binary neutron star merger, we analyse the possible impact of dark matter on such signals. We show that dark matter cores in merging neutron stars may yield an observable supplementary peak in the gravitational wave power spectral density following the merger, which could be distinguished from the features produced by the neutron components.
We consider the implications of fermionic asymmetric dark matter for a "mixed neutron star" composed of ordinary baryons and dark fermions. We find examples, where for a certain range of dark fermion mass -- when it is less than that of ordinary baryons -- such systems can reach higher masses than the maximal values allowed for ordinary ("pure") neutron stars. This is shown both within a simplified, heuristic Newtonian analytic framework with non-interacting particles and via a general relativistic numerical calculation, under certain assumptions for the dark matter equation of state. Our work…
It was recently proposed that the disagreement in the experimental measurements of the lifetime of the neutron might be eradicated if the neutron decays to particles responsible for the dark matter in the Universe. In this paper we construct a proto- type self-interacting dark matter model which, apart from reproducing the correct relic abundance, resolves all small-scale problems of the $Λ$CDM paradigm. The theory is compatible with all present cosmological observations and astrophysical bounds.
New decay channels for the neutron into dark matter plus other particles have been suggested for explaining a long-standing discrepancy between the neutron lifetime measured from trapped neutrons versus those decaying in flight. Many such scenarios are already ruled out by their effects on neutron stars, and the decay into dark matter plus photon has been experimentally excluded. Here we explore the decay into a dark Dirac fermion $χ$ and a dark photon $A'$, which can be consistent with all constraints if $χ$ is a subdominant component of the dark matter. Neutron star constraints are evaded if…
