Massive Black Holes In Galaxies Research Articles

Dynamical friction of a massive black hole in a turbulent gaseous medium

The orbital decay of massive black holes in galaxies in the aftermath of mergers is at the heart of whether massive black holes successfully pair and merge, leading to emission of low-frequency gravitational waves. The role of dynamical friction sourced from the gas distribution has been uncertain because many analytical and numerical studies have either focussed on a homogeneous medium or have not reached resolutions below the scales relevant to the problem, namely the Bondi-Hoyle-Lyttleton radius. We performed numerical simulations of a massive black hole moving in a turbulent medium in order to study dynamical friction from turbulent gas. We find that the black hole slows down to the sound speed, rather than the turbulent speed, and that the orbital decay is well captured if the Bondi-Hoyle-Lyttleton radius is resolved with at least five resolution elements. We find that the larger the turbulent eddies, the larger the scatter in dynamical friction magnitude, because of the stochastic nature of the problem, and also because of the larger over- and under-densities encountered by the black hole along its trajectory. Compared to the classic solution in a homogeneous medium, the magnitude of the force depends more weakly on the Mach number, and dynamical friction is overall more efficient for high Mach numbers, but less efficient towards and at the transonic regime.

Extreme-mass-ratio burst detection with TianQin

The capture of compact objects by massive black holes in galaxies or dwarf galaxies will generate short gravitational wave signals, called extreme-mass-ratio bursts (EMRBs), before evolving into extreme-mass-ratio inspirals. Their detection will provide an investigation of the black hole properties and shed light on astronomy and astrophysics. In this work, we investigate the detection number of the TianQin observatory on EMRBs. Our result shows that TianQin can detect tens of EMRBs events during its mission lifetime. For those detected events, we use the Fisher information matrix to quantify these uncertainties in the inference of their parameters. We consider the possible network of $\mathrm{TianQin}+\mathrm{LISA}$, and study how a network can improve parameter estimation. The result shows that, for most sources, the compact object mass, the massive black hole mass, and the massive black hole spin can be determined with a precision of the order ${10}^{\ensuremath{-}1}$ and the sky localization can be determined with a precision of 10 square degree. We further explore the gravitational wave background generated by those unsolved EMRBs and conclude that it is about ${10}^{6}$ times weaker than TianQin's sensitivity, and thus it can be ignored.

Feedback from central massive black holes in galaxies using cosmological simulations

AbstractGas accretion onto central supermassive black holes of active galaxies and resulting energy feedback, is an important component of galaxy evolution, whose details are still unknown especially at early cosmic epochs. We investigate BH growth and feedback in quasar-host galaxies at z ⩾ 6 by performing cosmological hydrodynamical simulations. We simulate the 2R200 region around a 2 × 1012Mʘ halo at z = 6, inside a (500 Mpc)3 comoving volume, using the zoom-in technique. We find that BHs accrete gas at the Eddington rate over z = 9–6. At z = 6, our most-massive BH has grown to MBH = 4 × 109 Mʘ. Star-formation is quenched over z = 8–6.

Rapid Formation of Black Holes in Galaxies: A Self-limiting Growth Mechanism

Abstract We present high-quality fluid dynamical simulations of isothermal gas flows in a rotating barred potential. We show that a large quantity of gas is driven right into the nucleus of a galaxy when the model lacks a central mass concentration, but the inflow stalls at a nuclear ring in comparison simulations that include a central massive object. The radius of the nuclear gas ring increases linearly with the mass of the central object. We argue that bars drive gas right into the nucleus in the early stages of disk galaxy formation, where a nuclear star cluster and perhaps a massive black hole could be created. The process is self-limiting, however, because inflow stalls at a nuclear ring once the mass of gas and stars in the nucleus exceeds ∼1% of the disk mass, which shuts off rapid growth of the black hole. We briefly discuss the relevance of these results to the seeding of massive black holes in galaxies, the merger model for quasar evolution, and the existence of massive black holes in disk galaxies that lack a significant classical bulge.

Bondi accretion in early-type galaxies

Accretion onto central massive black holes in galaxies is often modelled with the Bondi solution. In this paper we study a generalization of the classical Bondi accretion theory, considering the additional effects of the gravitational potential of the host galaxy, and of electron scattering in the optically thin limit. We provide a general analysis of the bias in the estimates of the Bondi radius and mass accretion rate, when adopting as fiducial values for the density and temperature at infinity the values of these quantities measured at finite distance from the central black hole. We also give general formulae to compute the correction terms of the critical accretion parameter in relevant asymptotic regimes. A full analytical discussion is presented in the case of an Hernquist galaxy, when the problem reduces to the discussion of a cubic equation, therefore allowing for more than one critical point in the accretion structure. The results are useful for observational works (especially in the case of low-luminosity systems), as well as for numerical simulations, where accretion rates are usually defined in terms of the gas properties near the

Massive black holes in galaxies

Massive black holes in galaxies

The growth of massive black holes in galaxy merger simulations with feedback by radiation pressure

We study the growth of massive black holes (BH) in galaxies using smoothed particle hydrodynamic simulations of major galaxy mergers with new implementations of BH accretion and feedback. The effect of BH accretion on gas in its host galaxy is modeled by depositing momentum at a rate ~ tau L/c into the ambient gas, where L is the luminosity produced by accretion onto the BH and tau is the wavelength-averaged optical depth of the galactic nucleus to the AGN's radiation (a free parameter of our model). The accretion rate onto the BH is relatively independent of our subgrid accretion model and is instead determined by the BH's dynamical impact on its host galaxy: BH accretion is thus self-regulated rather than `supply limited.' We show that the final BH mass and total stellar mass formed during a merger are more robust predictions of the simulations than the time dependence of the star formation rate or BH accretion rate. In particular, the latter depend on the assumed interstellar medium physics, which determines when and where the gas fragments to form star clusters; this in turn affects the fuel available for further star formation and BH growth. Simulations over a factor of ~ 30 in galaxy mass are consistent with the observed M_BH-sigma relation for a mean optical depth of tau ~ 25. This requires that most BH growth occur when the galactic nucleus is optically thick to far-infrared radiation, consistent with the hypothesized connection between ultra-luminous infrared galaxies and quasars. We find tentative evidence for a shallower M_BH-sigma relation in the lowest mass galaxies, sigma < 100 km/s. Our results demonstrate that feedback-regulated BH growth and consistency with the observed M_BH-sigma relation do not require that BH feedback terminate star formation in massive galaxies or unbind large quantities of cold gas.

COSMOLOGICAL EVOLUTION OF MASSIVE BLACK HOLES: EFFECTS OF EDDINGTON RATIO DISTRIBUTION AND QUASAR LIFETIME

A power-law time-dependent light curve for active galactic nuclei (AGNs) is expected by the self-regulated black hole growth scenario, in which the feedback of AGNs expels gas and shut down accretion. This is also supported by the observed power-law Eddington ratio distribution of AGNs. At high redshifts, the AGN life timescale is comparable with (or even shorter than) the age of the universe, which sets a constraint on the minimal Eddington ratio for AGNs on the assumption of a power-law AGN light curve. The black hole mass function (BHMF) of AGN relics is calculated by integrating the continuity equation of massive black hole number density on the assumption of the growth of massive black holes being dominated by mass accretion with a power-law Eddington ratio distribution for AGNs. The derived BHMF of AGN relics at z = 0 can fit the measured local mass function of the massive black holes in galaxies quite well, provided the radiative efficiency ∼0.1 and a suitable power-law index for the Eddington ratio distribution are adopted. In our calculations of the black hole evolution, the duty cycle of AGN should be less than unity, which requires the quasar life timescale τQ ≳ 5 × 108 years.

Rapidly spinning massive black holes in active galactic nuclei: evidence from the black hole mass function

The comparison of the black hole mass function (BHMF) of active galactic nuclei (AGN) relics with the measured mass function of the massive black holes in galaxies provides strong evidence for the growth of massive black holes being dominated by mass accretion. We derive the Eddington ratio distributions as functions of black hole mass and redshift from a large AGN sample with measured Eddington ratios given by Kollmeier et al. We find that, even at the low mass end, most black holes are accreting at Eddington ratio ~0.2, which implies that the objects accreting at extremely high rates should be rare or such phases are very short. Using the derived Eddington ratios, we explore the cosmological evolution of massive black holes with an AGN bolometric luminosity function (LF). It is found that the resulted BHMF of AGN relics is unable to match the measured local BHMF of galaxies for any value of (constant) radiative efficiency. Motivated by Volonteri, Sikora & Lasota's study on the spin evolution of massive black holes, we assume the radiative efficiency to be dependent of black hole mass, i.e., it is low for M 10^8 solar masses. We find that the BHMF of AGN relics can roughly reproduce the local BHMF of galaxies if the radiative efficiency ~0.08 for the black holes with 10^9 solar masses, which implies that most massive black holes (>10^9 solar masses) are spinning very rapidly.

Dynamics of Kicked and Accelerated Massive Black Holes in Galaxies

A study is made of the behavior of massive black holes in disk galaxies that have received an impulsive kick from a merger or a sustained acceleration from an asymmetric jet. The motion of the gas, stars, dark matter, and massive black hole are calculated using the GADGET-2 simulation code. The massive black hole escapes the galaxy for kick velocities above about 600 km s−1 or accelerations above about 4 × 10−8 cm s−2 over timescales of the order of 108 yr. For smaller velocity kicks or smaller accelerations, the black hole oscillates about the center of mass with a frequency that decreases as the kick velocity or acceleration increases. The black hole displacements may give rise to observable nonaxisymmetries in the morphology and dynamics of the stellar and gaseous disk of the galaxy. In some cases the dynamical center of the galaxy is seen to be displaced toward the direction of the BH acceleration with a characteristic tongue-shaped extension of the velocity contours on the side of the galaxy opposite the acceleration.

A New Way to Detect Massive Black Holes in Galaxies: The Stellar Remnants of Tidal Disruption

We point out that the tidal disruption of a giant may leave a luminous (10^35-10^39 ergs/s), hot (10-100 eV) stellar core. The ``supersoft'' source detected by Chandra at the center of M31 may be such a core; whether or not it is, the observations have shown that such a core is detectable, even in the center of a galaxy. We therefore explore the range of expected observational signatures and how they may be used to (1) test the hypothesis that the M31 source is a remnant of tidal stripping and (2) discover evidence of black holes and disruption events in other galaxies.