Mounting theoretical evidence suggests that the information stored in black holes suppresses their decay rate. This quantum effect of memory burden opens up a new window for small primordial black holes (PBHs) below $10^{15}\,{\rm g}$ as dark matter candidates. In this talk, I show that the smooth transition from semi-classical evaporation to the memory-burdened phase strongly impacts...
The fundamental scale of gravity could be significantly lower than the Planck scale due to the existence of a large number of particle species. This would also mean that processes exceeding this energy scale could produce black holes. In this talk, I will discuss two consequences of such a situation: first, the production of micro black holes in the corona of active galactic nuclei, together...
The thermodynamics of large black holes is reliably described by semiclassical quantum gravity, and contains the seeds of holography. Generically, it cannot be extrapolated beyond the validity of gravitational effective field theory. In some special regimes this is possible, and leads to novel constraints on weakly coupled completions of gravity. I will present the framework and discuss how...
Charged black hole solutions, which are ubiquitous in string theory, provide a natural setting for thought experiments probing the ultraviolet (UV) structure of quantum gravity. I will review recent progress in understanding how UV scales emerge in Effective Field Theories of quantum gravity, and explain how the attractor mechanism of charged black holes offers a controlled way to access UV...
Black holes remain one of the most fascinating windows into the quantum nature of gravity, yet their entropy is not fully captured by semiclassical considerations. Supersymmetric black holes, in particular, provide a controlled laboratory to explore subtle quantum effects and gain insights into more general black hole dynamics. In this work, we investigate genuinely non-perturbative...
Dark matter could consist of primordial black holes (PBHs). I present the first simulation of structure formation with PBH dark matter that self-consistently incorporates collisional few-body effects, post-Newtonian orbit corrections, orbital decay due to gravitational radiation, and black-hole mergers. An interesting phenomenology emerges in this simulation. Many-body interactions eject PBHs...
Resolving the rich structure in the central 0.1 x 0.1’’ in the Galactic Center allows tracing stars orbiting the central massive black hole SgrA*. Serving as test particles in a strong gravitational field, these S-stars are susceptible to effects of General Relativity. With its unmatched astrometric precision, the interferometric beam-combiner GRAVITY has already facilitated in the past a...
Since 2016, the GRAVITY interferometer at ESO’s Very Large Telescope has provided astrometric data with unprecedented accuracy for the S-stars orbiting Sagittarius A*, providing a powerful means to probe the gravitational potential surrounding the supermassive black hole at the center of our Galaxy. Notably, we have detected the in-plane, prograde Schwarzschild precession of the orbit of the...
Photons emitted from near ultra-compact objects carry information not only about their emission environment but also about the spacetime geometry around such objects. In the case of Sagittarius A*, the supermassive black hole at the centre of the Milky Way, the detected emission in the Near Infrared can flare to ten times its quiescent flux and be resolved temporally and spatially by the...
Extended X-ray emission observed in the direction of several molecular clouds in the Central Molecular Zone (CMZ) of our Galaxy exhibits spectral and temporal properties consistent with the `X-ray echo' scenario. It postulates that the observed signal is a light-travel-time delayed reflection of a short ($δt<$1.5 yr) and bright ($L_{\rm X}>10^{39}~{\rm erg~s^{-1}}$) flare, most probably...
Sagittarius A*, the supermassive black hole at the center of our Galaxy, offers a unique laboratory to study black hole accretion at extremely low rates. Understanding what material is available to feed it, and how that material interacts with its accretion zone, is key to understanding black hole feeding mechanisms more broadly. Many gas clumps of the order of a few Earth Solar masses have...
Gravitational-wave observations have opened a new window onto compact objects across the Universe. The Laser Interferometer Space Antenna (LISA) is a flagship European-led mission that will explore the intermediate-frequency gravitational-wave spectrum between 0.1 and 100 mHz. With its unique discovery potential, LISA will detect an exceptionally rich variety of sources, from stellar binaries...
Stellar evolution models predict that our galaxy should be filled with hundred of millions of isolated stellar-mass black holes (ISBH), yet only one has been detected conclusively as of today. Microlensing is the only method to detect ISBH, and only spatially resolving the event can break the degeneracy between distance and mass to the lens. I will present the latest developments in predicting...
Recent discoveries of puzzling electromagnetic transients in galactic centers, such as quasi-periodic eruptions and oscillations, point to a new class of stellar-mass objects interacting with supermassive black holes (SMBH). One compelling scenario is that stars gradually spiral inward through gravitational-wave emission and eventually transfer mass to the SMBH, forming stellar extreme mass...
Stellar-mass black holes (BHs) are formed in the collapse of massive stars. The detailed pathways to BH formation are, however, still under active debate. In my talk, I will present results from a set of three-dimensional (3D) neutrino-hydrodynamics simulations of BH formation in failed core-collapse supernova explosions (sometimes called "unnovae"). Because failed supernovae lack a bright...
There is growing evidence that a substantial fraction of the compact object mergers detected through gravitational waves merge with non-zero eccentricity or large spin-orbit misalignment. In particular, recent evidence for an eccentric neutron star-black hole (NSBH) merger and NSBHs with anti-aligned BH spins challenge leading formation scenarios to date. Residual eccentricity rules out...
Unraveling the mysteries of supermassive black holes and their relationship with their host galaxies is challenging and requires a proper disentanglement of the emission from the Active Galactic Nucleus (AGN) and the stellar populations. When observing the same AGN in different phases of its activity, some properties obtained from its optical spectra should be consistent, as the mass of the...
I discuss the relevance of high ionisation coronal lines as genuine tracers of the ionising continuum in galactic nuclei, and in turn of the spectral shape and temperature of the accretion disk, hence of the BH mass. On the basis of bona-fide BH masses from reverberation mapping and the strong infrared coronal line [Si VI] 1.96 um, a tight correlation between the excitation of the gas and...
The most massive galaxies in the Universe also host the largest black holes, with masses of $10^9 \: \mathrm{M_{\odot}}$ and above (SMBHs). During their hierarchical assembly, these galaxies accreted many low-mass galaxies across cosmic time, possibly hosting IMBHs. They have experienced only a few major mergers at low redshift. If some of these IMBHs migrate to the galactic center, they may...
AGN feedback has become a standard ingredient in cosmological simulations to help regulate the development of cooling flows and star formation from the scales of galaxies to groups and clusters. However, it is difficult to fine-tune the feedback efficiency to reproduce the observed cool-core fractions at all scales. In the paper "How the cool-core population transitions from galaxy groups to...
The mass and spin of massive black holes (BHs) at the centre of galaxies evolve due to gas accretion and mergers with other BHs. Besides affecting the evolution of relativistic jets, the BH spin determines the efficiency with which the BH radiates energy.
I implemented a sub-resolution prescription for cosmological, hydrodynamical simulations that models the evolution of the BH spin,...
Extended Ly-alpha nebulae observed around quasars trace the cool gas
within the multiphase circumgalactic medium and can provide key insights
into the complex interplay between gas dynamics and active galactic
nuclei (AGN) feedback. However, the connection between this cool phase
and the cold molecular gas around the host galaxies remains largely
unexplored. In this talk, I leverage ALMA...
Quasars are the most luminous type of AGN currently known, detectable across a vast range of redshifts extending beyond $z=7$. Thus, increasing the number of known quasars is essential for studying the accretion mechanisms of supermassive black holes, the evolution of galaxies, and the large-scale structure of the Universe, among others.
Over the last four decades, spectroscopic surveys have...
The early growth of high-redshift quasars and their host galaxies raises critical questions about their cosmic evolution. We exploit the angular resolution and sensitivity of NIRCam to investigate the host galaxies of 31 quasars at $4 < z <7$ drawn from multiple JWST surveys. Using a new multi-band forward-modeling code (\textsc{GalfitS}) that incorporates physically motivated priors, we...
The formation channels of the first supermassive black holes (SMBHs) at z > 6 remain elusive, as current observations are dominated by the most luminous quasars, representing only the tip of the population. To uncover fainter quasars, gravitational lensing provides a uniquely effective natural telescope, extending the accessible luminosity range and offering essential probes of black hole...
Little Red Dots (LRDs), compact galaxies at z > 5 discovered by JWST, show hydrogen Balmer lines with broad wings (>1000 km/s), absorption features, and asymmetric profiles, indicating extremely dense hydrogen gas. When the broad components of Balmer lines are analyzed using standard AGN methods, they imply supermassive black holes with unusually high black hole–to–stellar mass ratios....
