We present the accretion of collisional dark matter on a supermassive black hole seed. The analysis is based on the numerical solution of the fully coupled system of Einstein-Euler equations for spherically symmetric flow, where the dark matter is modeled as a perfect fluid that obeys an ideal gas equation of state. As the black hole actually grows, the accretion rate of dark matter corresponds to the black hole apparent horizon growth rate. We analyse cases with infall velocity as high as $0.5c$ and an environment density of $100M_{\odot}/\mathrm{pc}^3$, which are rather extreme conditions. Being the radial flux the maximum accretion case, our results show that the accretion of an ideal gas, eventually collisional dark matter, does not contribute significantly to SMBH masses. This result favors models predicting SMBHs were formed already with supermasses. We show that despite the fact that we are solving the full general relativistic system, for the parameter space studied our results are surprisingly similar to those obtained using the Bondi formula, which somehow certifies its use as a good approximation of a fully evolving space-time with spherical symmetry at short scales at least for dark matter densities. Additionally, we study the density profile of the gas and find that the presence of SMBHs redistributes the gas near the event horizon with a cuspy profile, whereas beyond a small fraction of a parsec it is not-cuspy anymore.
The processes driving gas accretion on to supermassive black holes (SMBHs) are still poorly understood. Angular momentum conservation prevents gas within $\sim10\,$pc of the black hole from reaching radii $\sim10^{-3}\,$pc where viscous accretion becomes efficient. Here we present simulations of the collapse of a clumpy shell of swept-up isothermal gas, which is assumed to have formed as a result of feedback from a previous episode of AGN activity. The gas falls towards the SMBH forming clumps and streams, which intersect, collide, and often form a disc. These collisions promote partial cancel…
We solve the spherically symmetric time dependent relativistic Euler equations on a Schwarzschild background space-time for a perfect fluid, where the perfect fluid models the dark matter and the space-time background is that of a non-rotating supermassive black hole. We consider the fluid obeys an ideal gas equation of state as a simple model of dark matter with pressure. Assuming out of equilibrium initial conditions we search for late-time attractor type of solutions, which we found to show a constant accretion rate for the non-zero pressure case, that is, the pressure itself suffices to pr…
I review the evolution of binary supermassive black holes and focus on the stellar-dynamical mechanisms that may help to overcome the final-parsec problem - the possible stalling of the binary at a separation much larger than is required for an efficient gravitational wave emission. Recent N-body simulations have suggested that a departure from spherical symmetry in the nucleus of the galaxy may keep the rate of interaction of stars with the binary at a high enough level so that the binary continues to shrink rather rapidly. However, a major problem of all these simulations is that they do not…
We consider the problem of star consumption by supermassive black holes in non-spherical (axisymmetric, triaxial) galactic nuclei. We review the previous studies of the loss-cone problem and present a novel simulation method which allows to separate out the collisional (relaxation-related) and collisionless (related to non-conservation of angular momentum) processes and determine their relative importance for the capture rates in different geometries. We show that for black holes more massive than 10^7 Msun, the enhancement of capture rate in non-spherical galaxies is substantial, with even mo…
Wind-fed Supermassive Black Hole Accretion in the Ultracompact Dwarf Galaxy M60-UCD1
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（南京大学现代天文与天体物理教育部重点实验室）；Institute of Science and Technology for Deep Space Exploration, Suzhou Campus, Nanjing University（南京大学苏州校区深空探测研究院）
The progenitors of astronomical transients are linked to a specific stellar population and galactic environment, and observing their host galaxies hence constrains the physical nature of the transient itself. Here, we use imaging from the Hubble Space Telescope, and spatially-resolved, medium resolution spectroscopy from the Very Large Telescope obtained with X-Shooter and MUSE to study the host of the very luminous transient ASASSN-15lh. The dominant stellar population at the transient site is old (around 1 to 2 Gyr), without signs of recent star-formation. We also detect emission from ionize…
The flat stellar density cores of massive elliptical galaxies form rapidly due to sinking supermassive black holes (SMBH) in gas-poor galaxy mergers. After the SMBHs form a bound binary, gravitational slingshot interactions with nearby stars drive the core regions towards a tangentially biased stellar velocity distribution. We use collisionless galaxy merger simulations with accurate collisional orbit integration around the central SMBHs to demonstrate that the removal of stars from the centre by slingshot kicks accounts for the entire change in velocity anisotropy. The rate of strong (unbindi…
It is assumed that a galaxy starts as a dark halo of a few million Jeans clusters (JCs), each of which consists of nearly a trillion micro brown dwarfs, MACHOs of Earth mass. JCs in the galaxy center heat up their MACHOs by tidal forces, which makes them expand, so that coagulation and star formation occurs. Being continuously fed by matter from bypassing JCs, the central star(s) may transform into a super massive black hole. It has a fast $t^3$ growth during the first mega years, and a slow $t^{1/3}$ growth at giga years. JCs disrupted by a close encounter with this black hole can provide mat…
The dynamical evolution of supermassive black-hole binary systems is tethered on large scales to the merger rate of massive galaxies, and on small scales to the stellar and gaseous environments of galactic cores. The population of these systems will create an ensemble gravitational-wave signal at nanohertz frequencies that is detectable by Pulsar Timing Arrays (PTA), such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). By measuring nanohertz gravitational waves, we will be able to definitively demonstrate that supermassive black-hole binaries reach milliparsec s…
A fundamental role is attributed to supermassive black holes (SMBH), and the feedback they generate, in the evolution of galaxies. But theoretical models trying to reproduce the relation between the SMBH mass and stellar velocity dispersion of the galaxy bulge make broad assumptions about the physical processes involved. These assumptions are needed due to the scarcity of observational constraints on the relevant physical processes which occur when the SMBH is being fed via mass accretion in Active Galactic Nuclei (AGN). In search for these constraints, our group -- AGN Integral Field Spectros…
The centre of our Milky Way harbours the closest candidate for a supermassive black hole. The source is thought to be powered by radiatively inefficient accretion of gas from its environment. This form of accretion is a standard mode of energy supply for most galactic nuclei. X-ray measurements have already resolved a tenuous hot gas component from which it can be fed. However, the magnetization of the gas, a crucial parameter determining the structure of the accretion flow, remains unknown. Strong magnetic fields can influence the dynamics of the accretion, remove angular momentum from the in…
We present the first observational constraint on the Br-gamma recombination line emission associated with the supermassive black hole at the center of our Galaxy, known as Sgr A*. By combining 13 years of data with the Adaptive Optics fed integral field spectrograph OSIRIS at the W. M. Keck Observatory obtained as part of the Galactic Center Orbits Initiative, we extract the near-infrared spectrum within ~0.2'' of the black hole and we derive an upper limit on the Br-gamma flux. The aperture was set to match the size of the disk-like structure that was recently reported based on millimeter-wav…
We propose high-velocity collisions of protogalaxies as a new pathway to form supermassive stars (SMSs) with masses of ~ 10^5 Msun at high redshift (z > 10). When protogalaxies hosted by dark matter halos with a virial temperature of ~ 10^4 K collide with a relative velocity > 200 km/s, the gas is shock-heated to ~ 10^6 K and subsequently cools isobarically via free-free emission and He^+, He, and H line emission. Since the gas density (> 10^4 cm^{-3}) is high enough to destroy H_2 molecules by collisional dissociation, the shocked gas never cools below ~ 10^4 K. Once a gas cloud of ~ 10^5 Msu…
The quest for binary and dual supermassive black holes (SMBHs) at the dawn of the multi-messenger era is compelling. Detecting dual active galactic nuclei (AGN) -- active SMBHs at projected separations larger than several parsecs -- and binary AGN -- probing the scale where SMBHs are bound in a Keplerian binary -- is an observational challenge. The study of AGN pairs (either dual or binary) also represents an overarching theoretical problem in cosmology and astrophysics. The AGN triggering calls for detailed knowledge of the hydrodynamical conditions of gas in the imminent surroundings of the …
A Wandering 35,000-Solar-Mass Black Hole Fed by a Gravitational Wake
Westlake University（西湖大学）；Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS（中国科学院南美洲天文学中心，国家天文台，中国科学院）；Xiamen University（厦门大学）；Nanjing University（南京大学）；Qinghai University（青海大学）；Qujing Normal University（曲靖师范学院）
Mass accretion by black holes (BHs) is typically capped at the Eddington rate, when radiation's push balances gravity's pull. However, even exponential growth at the Eddington-limited e-folding time t_E ~ few x 0.01 billion years, is too slow to grow stellar-mass BH seeds into the supermassive luminous quasars that are observed when the universe is 1 billion years old. We propose a dynamical mechanism that can trigger supra-exponential accretion in the early universe, when a BH seed is trapped in a star cluster fed by the ubiquitous dense cold gas flows. The high gas opacity traps the accretio…
Models aiming to explain the formation of massive black hole seeds, and in particular the direct collapse scenario, face substantial difficulties. These are rooted in rather ad hoc and fine-tuned initial conditions, such as the simultaneous requirements of extremely low metallicities and strong radiation backgrounds. Here we explore a modification of such scenarios where a massive primordial star cluster is initially produced. Subsequent stellar collisions give rise to the formation of massive (10^4 - 10^5 solar mass) objects. Our calculations demonstrate that the interplay between stellar dyn…
We investigate how uncertainties in the chemical and cooling rate coefficients relevant for a metal-free gas influence our ability to determine the critical ultraviolet field strength required to suppress H2 cooling in high-redshift atomic cooling halos. The suppression of H2 cooling is a necessary prerequisite for the gas to undergo direct collapse and form an intermediate mass black hole. These black holes can then act as seeds for the growth of the supermassive black holes (SMBHs) observed at redshifts $z \sim 6$. The viability of this model for SMBH formation depends on the critical ultrav…
Stellar-wind Fueled Accretion onto Sagittarius A* in the Presence of a Nuclear Star Cluster
Northwestern University（西北大学）；Institute for Advanced Study（高等研究院）；Canadian Institute for Theoretical Astrophysics（加拿大理论天体物理研究所）；University of Maryland（马里兰大学）
When a star passes close to a supermassive black hole (BH), the BH's tidal forces rip it apart into a thin stream, leading to a tidal disruption event (TDE). In this work, we study the post-disruption phase of TDEs in general relativistic hydrodynamics (GRHD) using our GPU-accelerated code H-AMR. We carry out the first grid-based simulation of a deep-penetration TDE ($β$=7) with realistic system parameters: a black-hole-to-star mass ratio of $10^6$, a parabolic stellar trajectory, and a nonzero BH spin. We also carry out a simulation of a tilted TDE whose stellar orbit is inclined relative to …
`Direct collapse black holes' (DCBHs) provide possible seeds for supermassive black holes that exist at redshifts as high as z~7. We study Lyman Alpha (Lya) radiative transfer through simplified representations of the DCBH-scenario. We find that gravitational heating of the collapsing cloud gives rise to a Lya cooling luminosity of up to ~ 1e38(M_gas/1e6 Msun)^2 erg/s. The Lya production rate can be significantly larger during the final stages of collapse, but collisional deexcitation efficiently suppresses the emerging Lya flux. Photoionization by a central source boosts the Lya luminosity to…
Supermassive black holes can capture or disrupt stars that come sufficiently close. This article reviews the dynamical processes by which stars or stellar remnants are placed onto loss-cone orbits and the implications for feeding rates. The capture rate is well defined for spherical galaxies with nuclear relaxation times that are shorter than the galaxy's age. However, even the dense nucleus of the Milky Way may be less than one relaxation time old, and this is certainly the case for more massive galaxies; the capture rate in such galaxies is an initial-value problem with poorly-known initial …
We numerically investigate the motion of stars on the meridional plane of an axially symmetric disk galaxy model, containing a central supermassive black hole, represented by the Paczynski-Wiita potential. By using this pseudo-Newtonian potential we can replicate important relativistic properties, such as the existence of the Schwarzschild radius. After classifying extensive samples of initial conditions of trajectories, we manage to distinguish between collisional, ordered, and chaotic motion. Besides, all starting conditions of regular orbits are further classified into families of regular o…
We calculate the radial profiles of galaxies where the nuclear region is self-gravitating, consisting of self-interacting dark matter (SIDM) with $F$ degrees of freedom. For sufficiently high density this dark matter becomes collisional, regardless of its behaviour on galaxy scales. Our calculations show a spike in the central density profile, with properties determined by the dark matter microphysics, and the densities can reach the `mean density' of a black hole (from dividing the black-hole mass by the volume enclosed by the Schwarzschild radius). For a galaxy halo of given compactness ($χ=…
As a natural consequence of the elementary processes of dust growth, we discovered that a new class of planets can be formed around supermassive black holes (SMBHs). We investigated a growth path from sub-micron sized icy dust monomers to Earth-sized bodies outside the "snow line", located several parsecs from SMBHs in low luminosity active galactic nuclei (AGNs). In contrast to protoplanetary disks, the "radial drift barrier" does not prevent the formation of planetesimals. In the early phase of the evolution, low collision velocity between dust particles promotes sticking; therefore, the int…
Supermassive black holes (SMBHs) are the central engines of luminous quasars and are found in most massive galaxies today. But the recent discoveries of ULAS J1120+0641, a $2 \times 10^9$ M$_{\odot}$ BH at $z =$ 7.1, and ULAS J1342+0928, a $8.0 \times 10^{8}$ M$_{\odot}$ BH at $z =$ 7.5, now push the era of quasar formation up to just 690 Myr after the Big Bang. Here we report new cosmological simulations of SMBHs with X-rays fully coupled to primordial chemistry and hydrodynamics that show that J1120 and J1342 can form from direct collapse black holes (DCBHs) if their growth is fed by cold, d…
We discuss the properties of orbits within the influence sphere of a supermassive black hole (BH), in the case that the surrounding star cluster is nonaxisymmetric. There are four major orbit families; one of these, the pyramid orbits, have the interesting property that they can approach arbitrarily closely to the BH. We derive the orbit-averaged equations of motion and show that in the limit of weak triaxiality, the pyramid orbits are integrable: the motion consists of a two-dimensional libration of the major axis of the orbit about the short axis of the triaxial figure, with eccentricity var…
Actively accreting supermassive black holes significantly impact the evolution of their host galaxies, truncating further star formation by expelling large fractions of gas with wide-angle outflows. The X-ray band is key to understanding how these black hole winds affect their environment, as the outflows have high temperatures ($\sim$10$^{5-8}$K). We have developed a Bayesian framework for characterizing Active Galactic Nuclei (AGN) outflows with an improved ability to explore parameter space and perform robust model selection. We applied this framework to a new 700 ks and an archival 315 ks …
Supermassive black holes (SMBHs) are thought to provide energy that prevents catastrophic cooling in the centers of massive galaxies and galaxy clusters. However, it remains unclear how this "feedback" process operates. We use high-resolution optical data to study the kinematics of multi-phase filamentary structures by measuring the velocity structure function (VSF) of the filaments over a wide range of scales in the centers of three nearby galaxy clusters: Perseus, Abell 2597 and Virgo. We find that the motions of the filaments are turbulent in all three clusters studied. There is a clear cor…
We study the birth of supermassive black holes from the direct collapse process and characterize the sites where these black hole seeds form. In the pre-reionization epoch, molecular hydrogen (H$_2$) is an efficient coolant, causing gas to fragment and form Population III stars, but Lyman-Werner radiation can suppress H$_2$ formation and allow gas to collapse directly into a massive black hole. The critical flux required to inhibit H$_2$ formation, $J_{\rm crit}$, is hotly debated, largely due to the uncertainties in the source radiation spectrum, H$_2$ self-shielding, and collisional dissocia…
FROST-CLUSTERS -- III. Metallicity-dependent intermediate mass black hole formation by runaway collisions in dense star clusters
Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；Institute of Astronomy, University of Cambridge（剑桥大学天文研究所）；Kavli Institute for Cosmology, Cambridge (KICC), University of Cambridge（剑桥卡弗里宇宙学研究所）；Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut（海德堡大学天文中心，天文计算研究所）；Max Planck Computing and Data Facility (MPCDF)（马克斯·普朗克计算与数据中心）；European Southern Observatory（欧洲南方天文台）；Department of Physics, University of Helsinki（赫尔辛基大学物理系）
The James Webb Space Telescope (JWST) will open a new window of the most distant universe and unveil the early growth of supermassive black holes (BHs) in the first galaxies. In preparation for deep JWST imaging surveys, it is crucial to understand the color selection of high-redshift accreting seed BHs. We model the spectral energy distribution of super-Eddington accreting BHs with millions of solar masses in metal-poor galaxies at $z\gtrsim 8$, applying post-process line transfer calculations to radiation hydrodynamical simulation results. Ten kilosecond exposures with the NIRCam and MIRI br…
BlackHoleWeather -- Jet-regulated chaotic cold accretion across the meso scale: Variability and kinematics
University of Modena and Reggio Emilia（摩德纳和雷焦艾米利亚大学）；Universidad de Santiago de Chile（智利圣地亚哥大学）；CIRAS, Universidad de Santiago de Chile（智利圣地亚哥大学 CIRAS）；INAF – Astronomical Observatory of Rome（意大利国家天体物理研究所罗马天文台）；Universidad Diego Portales（迭戈帕托莱斯大学）；NASA Ames Research Center（美国宇航局艾姆斯研究中心）
Nuclear star clusters (NSCs) and supermassive black holes (SMBHs) both inhabit galactic nuclei, coexisting in a range of bulge masses, but excluding each other in the largest or smallest galaxies. We propose that the transformation of NSCs into SMBHs occurs via runaway tidal captures, once NSCs exceed a certain critical central density and velocity dispersion. The bottleneck in this process, as with all collisional runaways, is growing the first e-fold in black hole mass. The growth of a stellar mass black hole past this bottleneck occurs as tidally captured stars are consumed in repeated epis…
We propose the formation of massive pristine dark-matter (DM) halos with masses of $\sim 10^8~M_\odot$, due to the dynamical effects of frequent mergers in rare regions of the Universe with high baryonic streaming velocity relative to DM. Since the streaming motion prevents gas collapse into DM halos and delays prior star formation episodes, the gas remains metal-free until the halo virial temperatures $\gtrsim 2\times 10^4~{\rm K}$. The minimum cooling mass of DM halos is boosted by a factor of $\sim 10-30$ because frequent major mergers of halos further inhibit gas collapse. We use Monte Car…
Using a new, high-resolution cosmological hydrodynamic simulation of a Milky Way-type (MW-type) galaxy, we explore how a merger-rich assembly history affects the mass budget of the central supermassive black hole (SMBH). We examine a MW-mass halo at the present epoch whose evolution is characterized by several major mergers to isolate the importance of merger history on black hole accretion. This study is an extension of Bellovary et. al. 2013, which analyzed the accretion of high mass, high redshift galaxies and their central black holes, and found that the gas content of the central black ho…
We perform the first three-dimensional radiation hydrodynamical simulations that investigate the growth of intermediate-mass BHs (IMBHs) embedded in massive self-gravitating, dusty nuclear accretion disks. We explore the dependence of mass accretion efficiency on the gas metallicity $Z$ and mass injection at super-Eddington accretion rates from the outer galactic disk $\dot{M}_{\rm in}$, and find that the central BH can be fed at rates exceeding the Eddington rate only when the dusty disk becomes sufficiently optically thick to ionizing radiation. In this case, mass outflows from the disk owin…
Constraining AGN accretion physics with black hole mass-luminosity scaling relations
INAF-Osservatorio Astronomico di Trieste（意大利国家天体物理研究所的里雅斯特天文台）；IFPU - Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；Dip. di Fisica, Informatica e Matematica, Università di Modena & Reggio Emilia（摩德纳与雷焦艾米利亚大学物理、信息与数学系）；ASI – Agenzia Spaziale Italiana（意大利航天局）；Dipartimento di Fisica ”Enrico Fermi”, Universita’ di Pisa（比萨大学恩里科·费米物理系）；INAF-Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）
BlackHoleWeather -- Chaotic cold accretion across the meso-scale: Variability and kinematics
University of Modena and Reggio Emilia（摩德纳和雷焦艾米利亚大学）；Universidad de Santiago de Chile（智利圣地亚哥大学）；INAF – Osservatorio Astronomico di Cagliari（意大利国家天体物理研究所卡利亚里天文台）；University of the Witwatersrand（威特沃特斯兰德大学）；Universität Hamburg（汉堡大学）
