* Astronomy

Title: Possible black universes in a brane world
Authors: K.A. Bronnikov, E.V. Donskoy

A black universe is a nonsingular black hole where, beyond the horizon, there is an expanding, asymptotically isotropic universe. Such spherically symmetric configurations have been recently found as solutions to the Einstein equations with phantom scalar fields (with negative kinetic energy) as sources of gravity. They have a Schwarzschild-like causal structure but a de Sitter infinity instead of a singularity. It is attempted to obtain similar configurations without phantoms, in the framework of an RS2 type brane world scenario, considering the modified Einstein equations that describe gravity on the brane. By building an explicit example, it is shown that black-universe solutions can be obtained there in the presence of a scalar field with positive kinetic energy and a nonzero potential.

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Title: Star Clusters Around Recoiled Black Holes in the Milky Way Halo
Authors: Ryan M. O'Leary, Abraham Loeb (Harvard University)
(Version v2)

Gravitational wave emission by coalescing black holes (BHs) kicks the remnant BH with a typical velocity of hundreds of km/s. This velocity is sufficiently large to remove the remnant BH from a low-mass galaxy but is below the escape velocity from the Milky Way (MW) galaxy. If central BHs were common in the galactic building blocks that merged to make the MW, then numerous BHs that were kicked out of low-mass galaxies should be freely floating in the MW halo today. We use a large statistical sample of possible merger tree histories for the MW to estimate the expected number of recoiled BH remnants present in the MW halo today. We find that hundreds of BHs should remain bound to the MW halo after leaving their parent low-mass galaxies. Each BH carries a compact cluster of old stars that populated the core of its original host galaxy. Using the time-dependent Fokker-Planck equation, we find that present-day clusters are ~< 1 pc in size, and their central bright regions should be unresolved in most existing sky surveys. These compact systems are distinguishable from globular clusters by their internal (Keplerian) velocity dispersion greater than one hundred km/s and their high mass-to-light ratio owing to the central BH. An observational discovery of this relic population of star clusters in the MW halo, would constrain the formation history of the MW and the dynamics of BH mergers in the early Universe. A similar population should exist around other galaxies, and may potentially be detectable in M31 and M33.

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Black holes may precede galaxies

Researchers told a meeting of the American Astronomical Society in Long Beach, California, that they had seen a clear link between the size of a black hole, as measured by its mass, and the galaxy where it was found.
A black hole's mass is about one one-thousandth of the mass of the surrounding galactic bulge, they said.
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Telescope on Mauna Kea locates most distant black hole in space
American and Japanese astronomers using the Subaru telescope on the summit of Mauna Kea have discovered the most distant black hole in space, surrounded by a giant galaxy, a finding that may help to increase understanding of how the celestial bodies evolved.

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