The central black-hole masses of 85 radio-loud quasars are estimated using available data of Hβ line-width and optical continuum luminosity. The vast majority of the quasars in this sample have black-hole masses larger than 108M⊙, while a few quasars may contain relatively smaller black-holes. It is found that the radio-loudness decreases with the black-hole mass.

The stability of the Schwarzschild black hole is studied. Using the Painlevé coordinate, our region can be defined as the black-hole-connected region (r > 2m, see text) of the Schwarzschild black hole or the white-hole-connected region (r > 2m, see text) of the Schwarzschild black hole. We study the stable problems of the black-holeconnected region . The conclusions are: (1) in the black-hole-c...

A black hole considered as a part of a thermodynamical system possesses the Bekenstein-Hawking entropy SH = AH/(4l 2 P), where AH is the area of a black hole surface and lP is the Planck length. Recent attempts to connect this entropy with dynamical degrees of freedom of a black hole generically did not provide the universal mechanism which allows one to obtain this exact value. We discuss the ...

We present a new algorithm for evolving orbiting black-hole binaries that does not require excision or a corotating shift. Our algorithm is based on a novel technique to handle the singular puncture conformal factor. This system, based on the Baumgarte-Shapiro-Shibata-Nakamura formulation of Einstein's equations, when used with a "precollapsed" initial lapse, is nonsingular at the start of the ...

We discuss the status of the black hole entropy formula SBH = AH/4G in low energy effective field theory. The low energy expansion of the black hole entropy is studied in a non-equilibrium situation: the semiclassical decay of hot flat space by black hole nucleation. In this context the entropy can be defined as an enhancement factor in the semiclassical decay rate, which is dominated by a spha...

Using the inverse scattering method we construct an exact stationary asymptotically flat 4+1-dimensional vacuum solution describing “black saturn”: a spherical black hole surrounded by a black ring. Angular momentum keeps the configuration in equilibrium. Black saturn reveals a number of interesting gravitational phenomena: (1) The balanced solution exhibits 2-fold continuous non-uniqueness for...

We discuss some of the drawbacks of using event horizons to define black holes and suggest ways in which black holes can be described without event horizons, using trapping horizons. We show that these trapping horizons give rise to thermodynamic behavior and possibly Hawking radiation too. This raises the issue of whether the event horizon or the trapping horizon should be seen as the true bou...

There are at least two formation scenarios consistent with the first gravitational-wave observations of binary black hole mergers. In field models, black hole binaries are formed from stellar binaries that may undergo common envelope evolution. In dynamic models, black hole binaries are formed through capture events in globular clusters. Both classes of models are subject to significant theoret...

Using the inverse scattering method we construct an exact stationary asymptotically flat 4+1-dimensional vacuum solution describing “black saturn”: a spherical black hole surrounded by a black ring. Angular momentum keeps the configuration in equilibrium. Black saturn reveals a number of interesting gravitational phenomena: (1) The balanced solution exhibits 2-fold continuous non-uniqueness for...

If the stellar population of the bulge contains black holes formed in the final core collapse of ordinary stars with M ∼> 30M⊙, then about 25,000 stellar mass black holes should have migrated by dynamical friction into the central parsec of the Milky Way, forming a black hole cluster around the central supermassive black hole. These black holes can be captured by the central black hole when the...