16 research outputs found
Cosmology with Hypervelocity Stars
In the standard cosmological model, the merger remnant of the Milky Way and
Andromeda (Milkomeda) will be the only galaxy remaining within our event
horizon once the Universe has aged by another factor of ten, ~10^{11} years
after the Big Bang. After that time, the only extragalactic sources of light in
the observable cosmic volume will be hypervelocity stars being ejected
continuously from Milkomeda. Spectroscopic detection of the velocity-distance
relation or the evolution in the Doppler shifts of these stars will allow a
precise measurement of the vacuum mass density as well as the local matter
distribution. Already in the near future, the next generation of large
telescopes will allow photometric detection of individual stars out to the edge
of the Local Group, and may target the ~10^{5+-1} hypervelocity stars that
originated in it as cosmological tracers.Comment: 4 pages, 2 figures, accepted for publication in the Journal of
Cosmology and Astroparticle Physics (JCAP, 2011
Covariant description of the black hole entropy in 3D gravity
We study the entropy of the black hole with torsion using the covariant form
of the partition function. The regularization of infinities appearing in the
semiclassical calculation is shown to be consistent with the grand canonical
boundary conditions. The correct value for the black hole entropy is obtained
provided the black hole manifold has two boundaries, one at infinity and one at
the horizon. However, one can construct special coordinate systems, in which
the entropy is effectively associated with only one of these boundaries.Comment: 12 pages, LaTeX, v2: new material in section IV clarifies the effects
pertaining to the use of different coordinate system