Speaker
Description
Primordial black holes (PBHs) have been excluded from constituting the entirety of the dark matter (DM), except in the so-called 'asteroid-mass' range (between 10¹⁷ and 10²³ g) where they remain unconstrained. We present here observation-based constraints on PBHs in this previously open window, using photometric observations of local ultra-faint dwarf galaxies (UFDs) from the Hubble Space Telescope (HST). More specifically, we rely on the fact that if asteroid-mass PBHs exist, they could be captured by stars in DM-dominated environments with low velocity dispersion, such as UFDs. We computed this capture probability, and found that it increases with the stellar mass. Once captured, PBHs are expected to rapidly accrete their host stars. Consequently, the presence of PBHs in a UFD would lead to the destruction of a fraction of its stars, with heavier star being preferentially destroyed. This process would alter the stellar mass function of the UFD, making it top-light. Using HST photometric observations of three UFDs, we show that it is unlikely that their stellar mass functions have been significantly modified by PBHs, and we place constraints on the PBH abundance. PBHs with masses around 10¹⁹g are excluded at the 2σ (3σ) level from constituting more than 55% (78%) of the dark matter, while the possibility that PBHs represent the entirety of the DM is excluded at the 3.7σ level. This talk is based on the following works: 2207.07412 (PRD), 2311.12658 (MNRAS), 2503.03352 (A&A).
