Speaker
Prof.
Lindita Hamolli
(Department of Physics, University of Tirana, Albania)
Description
Microlensing is an effective tool for constraining the properties of compact dark matter candidates, such as Primordial Black Holes (PBHs). Standard photometric observations of microlensing events offer valuable insights into the mass and spatial distribution of PBHs. However, degeneracies among lensing parameters often limit the precision of these measurements. A promising approach to alleviate these limitations involves detecting polarization signals generated during microlensing events.
In this study, we investigate the expected polarimetric signatures of PBH-induced microlensing events, focusing on those that may be identified through photometric monitoring by the upcoming Nancy Grace Roman Space Telescope (Roman). The strength of the polarization signal depends on the geometry of the source–lens system and the structure of the circumstellar envelope. The signal typically reaches its maximum when the lens passes near the outer edge of the envelope—a configuration that can be effectively probed using high-sensitivity ground-based polarimeters such as FORS2 at the Very Large Telescope (VLT).
Using Monte Carlo simulations, we model a population of PBHs distributed according to a Galactic halo profile. The source stars are assumed to be cool red giant branch (RGB) stars, each surrounded by an extended dusty envelope that generates intrinsic polarization through scattering by dust and molecules. Given Roman’s photometric precision and its planned survey of the Galactic center, we find that PBHs with masses in the range of 10⁻⁵ to 10 M☉ are most likely to induce detectable polarization in RGB stars. Our simulations indicate a polarization detection probability of approximately 8.4%, underscoring the importance of ground-based polarimetric follow-up with instruments like VLT/FORS2 for placing tighter constraints on the PBH population in the Milky Way.
Primary authors
Prof.
Lindita Hamolli
(Department of Physics, University of Tirana, Albania)
Marsida Laze
Mimoza Hafizi
