Black Holes and Dark Matter (Daniele Gaggero – Università di Torino)

Abstract : The discovery of gravitational wave signals from merger events of massive binary-black-hole (BBH) systems have prompted a renewed debate in the scientific community about the interplay between Black Hole phenomenology and Dark Matter searches. On the one hand, Black Holes of primordial origin (PBHs) may have formed in the early Universe and could constitute a significant portion of the elusive dark matter that, according to standard cosmology, makes up the majority of the matter content in the universe. On the other hand, peculiar classes of Black Holes can be studied as “portals” to Dark Matter detection in the Gravitational Wave channel, due to the large density of DM that is expected to be present around them. In the first part of the talk, I will review the most promising multi-messenger avenues towards detection of PBHs. I will first focus on the radio/X-ray band, and present the prospects of discovery for both a hypothetical PBH population and the guaranteed population of astrophysical isolated black holes in our Galaxy, based on the broad-band emission from the interstellar gas that is being accreted onto them. Then, I will turn my attention to the gravitational wave domain, and discuss the merger rate of black-hole binaries. I will present a detailed evaluation of the expected rate from a generic (subdominant) component of PBHs, and analyze the role of future observation at high redshift to identify a primordial component on top of the rate associated to astrophysical BHs. In the final part of my talk, I will turn my attention to the impact of Dark Matter overdensities around Intermediate-Mass Black Holes, and on their impact on the gravitational waveform emitted in presence of an Intermediate-Mass-Ratio inspiral. I will demonstrate that the dephasing effect induced by the presence of the DM is observable in this channel, and the properties of the DM overdensity can be measured by the upcoming LISA observatory.