Date: 06.05.2025

Michał Pawlak (LU,SE)

Search for dormant black holes

Abstract:
Black holes (BHs) are the end products of the evolution of the most massive stars. Their unique properties make BHs very interesting but also very challenging objects to detect and study, as they do not emit electromagnetic radiation; hence, in most cses, they have to be observed indirectly. I will discuss the currently existing methods of BH detection (X-ray observation, gravitational waves, astrometry, microlensing) and present the 4MOST Dormant Black Holes Survey, which aims to explore a new BH discovery channel using a combination of photometric and spectroscopic observations. The goal of the survey is to spectroscopically follow up stars that might have dormant compact companions, either black holes or neutron stars. These stars have been identified as ellipsoidal binaries in the Magellanic Clouds by the OGLE survey. A sample of more than 700 ellipsoidals with periods shorter than 10 days will be observed to obtain multi-epoch radial-velocity measurements. 4MOST radial velocities, in conjunction with OGLE photometry, will allow the determination of the secondary component's mass and hence the identification of systems with compact companions.