Przemysław Mróz (Astronomical Observatory, Warsaw University)
Gravitational-wave detectors - LIGO, Virgo, and KAGRA - have revealed a population of massive black holes whose origin is still a subject o vigorous debate. Understanding the population of black holes in the Milky Way is therefore of key importance for understanding and putting into the astrophysical context the LIGO/Virgo/KAGRA discoveries. Gravitational microlensing remains the only viable technique which enables us to detect and directly measure masses of isolated stellar remnants, especially neutron stars and black holes. In this talk, I will present the recent advancements in the field of gravitational microlensing, which have led to the discovery of the first isolated stellar-mass black hole in the Milky Way and which will pave the way for future similar discoveries. I will present how astrometric and interferometric observations of gravitational microlensing events allow us to detect and characterize isolated neutron stars and black holes. Finally, I will discuss whether black holes of different sizes can make up dark matter.
Maciek Wielgus (Instituto de Astrofísica de Andalucía, IAA-CSIC, Granada, Hiszpania)
I will discuss the first 3D-general relativistic magnetohydrodynamic (GRMHD) simulation of sustained accretion onto a horizonless singularity in which matter falls onto the central object rather than being accumulated outside of it or expelled in outflows. We consider a Joshi-Malafarina-Narayan JMN-1 type spacetime, a well-motivated black hole mimicker arising from gravitational collapse with anisotropic pressure in general relativity, with a compactness parameter resulting in a null type central singularity. We find that the simulation reaches a sustained magnetically arrested disk state. For the parameters of the low-luminosity active galactic nucleus system M87* we find the mass accretion rate of (3-5) x 1e-6 of the Eddington rate, fully consistent with the estimates driven by the Kerr GRMHD, and in particular comparable with our reference Schwarzschild black hole simulation. Synthetic raytraced images at 230 GHz, computed through polarized general relativistic radiative transfer, are broadly consistent with the observations of M87* by the Event Horizon Telescope (EHT). We identified a key observational discriminant between a black hole and JMN-1, related to the presence of brightness in the images inside the “shadow” of JMN-1. This brightness is related to emission located very close to the central singularity, in the region that would be blocked by the event horizon in case of a black hole spacetime. Such a signature, while inaccessible to current EHT observations, falls within the projected imaging dynamic range of the near-future radio-interferometric instruments, offering a robust observational test of the black hole paradigm.
Patrick C. Fragile (Charleston College)
Accretion of gas onto black holes is one of the most important processes shaping our Universe. Understanding extremely high rates of accretion (dubbed `super-Eddington') is vital to explaining the challenging observation that supermassive black holes (SMBHs) are fully formed at redshifts >7. It is also important to understanding astrophysical objects such as tidal disruption events (TDEs) and ultra-luminous X-ray sources (ULXs). While we are able to perform observations of super-Eddington accreting systems, to understand them more fully, we must turn to numerical studies. In this talk, I will present the results of some recent super-Eddington disk simulations and discuss some of the interesting things we are learning.
Bogumił Pilecki (CAMK, Warsaw)
Samik Mitra (Astrophysics and Relativity Group International Centre for Theoretical Sciences, Bengaluru, India)
Andrzej Kruszewicz (Warsaw Zoological Garden)
Rameshan Thimmappa
