Black Hole Phenomenology and Dark Matter Searches

June 20, 2022
11:00am to 1:00pm

IFT Seminar Room/Red Room

Specialist level
Francesca María Scarcella

IFT Seminar Room/Red Room


In this thesis we discuss some possible inter-plays between dark matter searches and the physics of black holes. In particular, we consider black holes formed in the early Universe, long before the birth of stars and galaxies. These are known as primordial black holes, and could originate from the gravitational collapse of large (order one) density perturbations from inflation. If black holes of this kind exist, they would make up a part, possibly even all, of the dark matter. The discovery of such objects would have far reaching consequences for the study of the dark matter, even if they were found to constitute only a subdominant component of it. Primordial black holes with masses ranging between a few and a hundred solar masses have been the subject of many recent studies and debate, following the recent detection of gravitational waves emitted by mergers of binary black hole systems.

We also discuss two complimentary observational channels for the observation of black holes in this mass range. Firstly, we consider the intense electromagnetic radiation that can be emitted by the process of gas accretion. We study the possibility of detecting isolated black holes in our Galaxy through this channel, separately examining the astrophysical black hole population and an hypothetical primordial one. Regarding the former, our findings suggest that the detection of isolated black holes in the vicinity of the galactic centre is around the corner. Multi-wavelength studies are essential for the identification of this type of sources, hence we consider detection in both the X-ray and radio band. We furthermore study the prospects for radio detection with the future Square Kilometer Array telescope. With respect to primordial black holes, we consider a population whose mass distribution arises from the study of the thermal history of the Universe in the radiation era. We find that this population is not constrained by the searches for accretion signals from the Galactic centre.

Secondly, we turn to the gravitational wave channel. While attempts have been made to disentangle the astrophysical background form a possible primordial signal in present data, any conclusion is hampered by large theoretical uncertainties on the properties of both populations. Third-generation gravitational wave detectors such as the Einstein Telescope will be able to detect mergers up to immense distances, corresponding to epochs preceding the birth of the first stars. At such distances, the astrophysical background is expected to be absent. We discuss the theoretical redshift dependence of the merger rates of astrophysical and primordial black holes, together with their most relevant uncertainties. Through the process of mock data generation and analysis, we assess the ability of the Einstein Telescope to identify a subdominant population of primordial black holes, disentangling it from the astrophysical one based exclusively on measurements of the distances to the events. In particular, we model and discuss the important role played by the instrumental errors on distance measurements. We find that the Einstein Telescope should be able to detect and constrain the abundance of primordial black holes if these constitute at least one part in ∼10^5 of the total dark matter.