The illustration shows the precession of an accretion disk that formed shortly after the disruption of a star in the immediate vicinity of a supermassive black hole (the transient AT2020ocn). The left panel corresponds to the phase when we observe a smaller and cooler projected area of the disk from Earth (lower flux), while the right panel shows the phase with a larger projected disk area (higher flux) and the hotter regions of the accretion flow becoming exposed. The discovery of Lense–Thirring precession was published in Nature and was also featured in an MIT News press release. Credit: Michal Zajaček

We study the central regions of galaxies, including the center of the Milky Way. We are interested in the activity of supermassive black holes, how they grow, and how they interact with their surroundings. We investigate how the growth of supermassive black holes is influenced by their environment across different spatial scales and, conversely, how these black holes affect their surroundings. We use multi-wavelength observational data in combination with theoretical and computational models.

We now know that most galaxies host at least one supermassive black hole at their centers. Although these massive compact objects, with masses ranging from millions to billions of solar masses, dynamically influence only relatively small regions in their immediate surroundings, with radii of approximately 0.5–100 parsecs, their intense radiation and powerful outflows can affect the rate of star formation and the amount of cold gas in their host galaxies and even their wider environments on the scales of galaxy clusters. It is therefore essential to study black-hole growth processes, such as accretion and mergers, and to investigate how supermassive black holes influence the evolution of galaxies in a cosmological context.

Current Research Areas

We study the motion of stars and gas in the vicinity of the supermassive black hole at the center of the Milky Way, whose observational counterpart is the compact and variable radio source Sgr A*. We have searched for stars orbiting very close to Sgr A*. One of the record holders is S4716, which orbits Sgr A* on a scale comparable to the size of the Solar System, completing one orbit in just 4 years. One of the remaining mysteries is how these relatively young stars could have formed so close to the supermassive black hole. A key to solving this puzzle may be provided by the still-enigmatic dust-enshrouded objects, which are found similarly close to Sgr A* and exhibit signatures of young stellar objects. On the other hand, the recent discovery of the D9 binary star orbiting the supermassive black hole, which belongs to the population of dust-enshrouded objects (the so-called G objects), opens up the possibility that these enigmatic objects form as a result of ongoing binary interactions and mergers.

We also study the interactions of stars and compact remnants with accretion disks, nuclear winds, and jets in the vicinity of supermassive black holes. In particular, we investigate how these smaller bodies can affect accretion rates and outflows and whether such interactions can significantly influence stellar evolution and the appearance of stars in the vicinity of supermassive black holes. To this end, we have performed detailed three-dimensional hydrodynamic simulations of collisions between red giants and a nuclear jet, which may have been present during a period of enhanced Sgr A* activity in the past.

Another important question concerns the relationship between processes that are not associated with galaxy mergers (and which can be studied through galaxy morphology) and the supply of matter to supermassive black holes and their feedback on the surrounding environment. Members of our group focus particularly on the observed trend that galaxies with prominent bars show a higher incidence of active galactic nuclei, as well as on other complex relationships between galactic bars, bulges, and supermassive black-hole activity.

We are also interested in the fundamental physics of gravitational theories and black holes, particularly the possibility of testing for the presence of charged black holes in the Universe and the potential use of accreting black holes to constrain cosmological models.

We collaborate closely with other research groups at the Department of Theoretical Physics and Astrophysics, specifically the Galaxy Cluster Astrophysics and Observing the Energetic Universe with Small Satellites groups within MUNI High-Energy Astrophysics.

Funding

We have received support from the Czech Science Foundation (GA ČR) for the research projects described above through a Junior Star grant (GM24-10599M) and a Czech–Polish collaborative project (GF23-04053L).