To Observe, or Not to Observe, Quantum-Coherent Dark Matter in the Milky Way, That is a Question

In recent years, Bose-Einstein-condensed dark matter (BEC-DM) has become a popular alternative to standard, collisionless cold dark matter (CDM). This BEC-DM -also called scalar field dark matter (SFDM)- can suppress structure formation and thereby resolve the small-scale crisis of CDM for a range of boson masses. However, these same boson masses also entail implications for BEC-DM substructure within galaxies, especially within our own Milky Way. Observational signature effects of BEC-DM substructure depend upon its unique quantum-mechanical features and have the potential to reveal its presence. Ongoing efforts to determine the dark matter substructure in our Milky Way will continue and expand considerably over the next years. In this contribution, we will discuss some of the existing constraints and potentially new ones with respect to the impact of BEC-DM onto baryonic tracers. Studying dark matter substructure in our Milky Way will soon resolve the question, whether dark matter behaves classical or quantum on scales of ≲ 1 kpc.

Observational signatures of strongly naked singularities: image of the thin accretion disk

We study the optical appearance of a thin accretion disk around the strongly naked static Janis–Newman–Winicour singularity. The solution does not possess a photon sphere, which results in the formation of a complex structure of bright rings in the central region of the disk image. Such structure is absent in the case of the Schwarzschild black hole with a thin accretion disk, where instead of the image we observe the black hole shadow. Some of the rings emit with the maximal observable radiation flux from the accretion disk, and should be experimentally detectable. Thus, this qualitatively new feature can be used to distinguish observationally black holes from naked singularities. We elucidate the appearance of the ring structure by revealing the physical mechanism of its formation, and explaining the nature of each of the ring images. We make the conjecture that a similar structure would also appear for other solutions without a photon sphere and it can serve as a general observational signature for distinguishing compact objects possessing no photon sphere from black holes.

Imprint of Pressure on Characteristic Dark Matter Profiles: The Case of ESO0140040

We investigate the dark matter distribution in the spiral galaxy ESO0140040, employing the most widely used density profiles: the pseudo-isothermal, exponential sphere, Burkert, Navarro-Frenk-White, Moore and Einasto profiles. We infer the model parameters and estimate the total dark matter content from the rotation curve data. For simplicity, we assume that dark matter distribution is spherically symmetric without accounting for the complex structure of the galaxy. Our predictions are compared with previous results and the fitted parameters are statistically confronted for each profile. We thus show that although one does not include the galaxy structure it is possible to account for the same dynamics assuming that dark matter provides a non-zero pressure in the Newtonian approximation. In this respect, we solve the hydrostatic equilibrium equation and construct the dark matter pressure as a function for each profile. Consequently, we discuss the dark matter equation of state and calculate the speed of sound in dark matter. Furthermore, we interpret our results in view of our approach and we discuss the role of the refractive index as an observational signature to discriminate between our approach and the standard one.

Evolution of Primordial Dark Matter Planets in the Early Universe

In a recent paper we had discussed possibility of DM at high redshifts forming primordial planets composed entirely of DM to be one of the reasons for not detecting DM (as the flux of ambient DM particles would be consequently reduced). In this paper we discuss the evolution of these DM objects as the universe expands. As universe expands there will be accretion of DM, Helium and Hydrogen layers (discussed in detail) on these objects. As they accumulate more and more mass, the layers get heated up leading to nuclear reactions which burn H and He when a critical thickness is reached. In the case of heavier masses of these DM objects, matter can be ejected explosively. It is found that the time scale of ejection is smaller than those from other compact objects like neutron stars (that lead to x-ray bursts). These flashes of energy could be a possible observational signature for these dense DM objects.

Formation of counter-rotating stars during gas-rich disc–disc mergers

ABSTRACT We present a new scenario for the origin of the counter-rotating stars in disc galaxies, defined as stars that have a negative tangential velocity. This scenario involves a merger between two gas-rich disc galaxies that have comparable masses, are nearly coplanar, and are rotating in the same direction. The merger results in an intense starburst, during which a significant fraction of the gas is converted to stars. The system then settles into an equilibrium configuration consisting of a thick disc and a bulge partly supported by velocity dispersion and a thin disc supported by rotation. Star formation proceeds until most of the gas supply is exhausted. Stars formed during the starburst have tangential velocities ranging from $-600$ to $600\, {\rm km\, s^{-1}}$. Stars formed afterward in the thick disc and bulge have high eccentricities and low tangential velocities, typically in the range $-100$ to $100\, {\rm km\, s^{-1}}$, while stars formed in the thin disc have large, positive velocities. All fast, counter-rotating stars ($V\lt -200\, {\rm km\, s^{-1}}$) are old, metal-poor, with very low dispersion in ages and metallicities. By contrast, fast, corotating stars ($V\gt 200\, {\rm km\, s^{-1}}$) have a wide range of ages and metallicities. The average abundances ratios $\rm [O/H]$ and [Fe/H] for fast, corotating stars typically exceed the corresponding ratios for fast, counter-rotating stars by $0.1-0.4\,\mathrm{ dex}$, while the dispersion in the values of NFe/NH are larger by factors between 2 and 14. This provides an observational signature of major, gas-rich mergers at high redshift.

Dark Matter Candidates with Dark Energy Interiors Determined by Energy Conditions

We outline the basic properties of regular black holes, their remnants and self-gravitating solitons G-lumps with the de Sitter and phantom interiors, which can be considered as heavy dark matter (DM) candidates generically related to a dark energy (DE). They are specified by the condition T t t = T r r and described by regular solutions of the Kerr-Shild class. Solutions for spinning objects can be obtained from spherical solutions by the Newman-Janis algorithm. Basic feature of all spinning objects is the existence of the equatorial de Sitter vacuum disk in their deep interiors. Energy conditions distinguish two types of their interiors, preserving or violating the weak energy condition dependently on violation or satisfaction of the energy dominance condition for original spherical solutions. For the 2-nd type the weak energy condition is violated and the interior contains the phantom energy confined by an additional de Sitter vacuum surface. For spinning solitons G-lumps a phantom energy is not screened by horizons and influences their observational signatures, providing a source of information about the scale and properties of a phantom energy. Regular BH remnants and G-lumps can form graviatoms binding electrically charged particles. Their observational signature is the electromagnetic radiation with the frequencies depending on the energy scale of the interior de Sitter vacuum within the range available for observations. A nontrivial observational signature of all DM candidates with de Sitter interiors predicted by analysis of dynamical equations is the induced proton decay in an underground detector like IceCUBE, due to non-conservation of baryon and lepton numbers in their GUT scale false vacuum interiors.