62 research outputs found
Mass Determination of Groups of Galaxies: Effects of the Cosmological Constant
The spherical infall model first developed by Lema\^{i}tre and Tolman was
modified in order to include the effects of a dark energy term. The resulting
velocity-distance relation was evaluated numerically. This equation, when
fitted to actual data, permits the simultaneous evaluation of the central mass
and of the Hubble parameter. Application of this relation to the Local Group,
when the dark energy is modeled by a cosmological constant, yields a total mass
for the M31-Milky Way pair of (2.5 +/- 0.7) x 10^12 M\_sun, a Hubble parameter
H\_0 = 74 +/- 4 km s^-1 Mpc^-1 and a 1-D velocity dispersion for the flow of
about 39 km s^-1. The zero-velocity and the marginally bound surfaces of the
Local Group are at about 1.0 and 2.3 Mpc respectively from the center of mass.
A similar analysis for the Virgo cluster yields a mass of (1.10 +/- 0.12) x
10^15 M\_sun and H\_0 = 65 +/- 9 km s^-1 Mpc^-1. The zero-velocity is located
at a distance of 8.6 +/- 0.8 Mpc from the center of the cluster. The predicted
peculiar velocity of the Local Group towards Virgo is about 190 kms^-1, in
agreement with other estimates. Slightly lower masses are derived if the dark
energy is represented by a fluid with an equation of state P = w\epsilon with w
= -2/3.Comment: 13 pages, 3 figures. Version to appear in New Astronomy. Typing
errors corrected in relation (1) and in percentage value in page
Indirect search for dark matter: prospects for GLAST
Possible indirect detection of neutralino, through its gamma-ray annihilation
product, by the forthcoming GLAST satellite from our galactic halo, M31, M87
and the dwarf galaxies Draco and Sagittarius is studied. Gamma-ray fluxes are
evaluated for the two representative energy thresholds, 0.1 GeV and 1.0 GeV, at
which the spatial resolution of GLAST varies considerably. Apart from dwarfs
which are described either by a modified Plummer profile or by a
tidally-truncated King profiles, fluxes are compared for halos with central
cusps and cores. It is demonstrated that substructures, irrespective of their
profiles, enhance the gamma-ray emission only marginally. The expected
gamma-ray intensity above 1 GeV at high galactic latitudes is consistent with
the residual emission derived from EGRET data if the density profile has a
central core and the neutralino mass is less than 50 GeV, whereas for a central
cusp only a substantial enhancement would explain the observations. From M31,
the flux can be detected above 0.1 GeV and 1.0 GeV by GLAST only if the
neutralino mass is below 300 GeV and if the density profile has a central cusp,
case in which a significant boost in the gamma-ray emission is produced by the
central black hole. For Sagittarius, the flux above 0.1 GeV is detectable by
GLAST provided the neutralino mass is below 50 GeV. From M87 and Draco the
fluxes are always below the sensitivity limit of GLAST.Comment: 14 Pages, 7 Figures, 3 Tables, version to appear on Physical Review
Consistency of the mass variation formula for black holes accreting cosmological fluids
We address the spherical accretion of generic fluids onto black holes. We
show that, if the black hole metric satisfies certain conditions, in the
presence of a test fluid it is possible to derive a fully relativistic
prescription for the black hole mass variation. Although the resulting equation
may seem obvious due to a form of it appearing as a step in the derivation of
the Schwarzschild metric, this geometrical argument is necessary to fix the
added degree of freedom one gets for allowing the mass to vary with time. This
result has applications on cosmological accretion models and provides a
derivation from first principles to serve as a base to the accretion equations
already in use in the literature.Comment: 4 pages, 1 figure. To appear in Gen. Rel. Gra
Multimessenger astronomy with the Einstein Telescope
Gravitational waves (GWs) are expected to play a crucial role in the
development of multimessenger astrophysics. The combination of GW observations
with other astrophysical triggers, such as from gamma-ray and X-ray satellites,
optical/radio telescopes, and neutrino detectors allows us to decipher science
that would otherwise be inaccessible. In this paper, we provide a broad review
from the multimessenger perspective of the science reach offered by the third
generation interferometric GW detectors and by the Einstein Telescope (ET) in
particular. We focus on cosmic transients, and base our estimates on the
results obtained by ET's predecessors GEO, LIGO, and Virgo.Comment: 26 pages. 3 figures. Special issue of GRG on the Einstein Telescope.
Minor corrections include
Thermodynamics of phantom energy in the presence of a Reissner-Nordstrom black hole
In this paper, we study the validity of the generalized second law (GSL) in
phantom dominated universe in the presence of a Reissner-Nordstr\"{o}m (RN)
black hole. Our study is independent of the origin of the phantom like behavior
of the considered universe. We also discuss the GSL in the neighborhood of
transition from quintessence to phantom regime. We show that for a constant
equation of state parameter, the GSL may be satisfied provided that the
temperature is proportional to de Sitter temperature. It is shown that in
models with (only) a transition from quintessence to phantom regime the
generalized second law does not hold in the transition epoch. Next we show that
if the phantom energy has a chemical potential, then the GSL will hold if the
mass of black hole is above from a critical value.Comment: 5 pages, Accepted for publication in Astrophysics & Space Scienc
Status Report Of The Schenberg Gravitational Wave Antenna
Here we present a status report of the Schenberg antenna. In the past three years it has gone to a radical upgrading operation, in which we have been installing a 1K pot dilution refrigerator, cabling and amplifiers for nine transducer circuits, designing a new suspension and vibration isolation system for the microstrip antennas, and developing a full set of new transducers, microstrip antennas, and oscillators. We are also studying an innovative approach, which could transform Schenberg into a broadband gravitational wave detector.3631Aguiar, O.D., (2002) Class. Quantum Grav., 19, p. 1949Aguiar, O.D., (2004) Class. Quantum Grav., 21, pp. S457Aguiar, O.D., (2005) Class. Quantum Grav., 22, pp. S209Aguiar, O.D., (2006) Class. Quantum Grav., 23, pp. S239Aguiar, O.D., (2008) Class. Quantum Grav., 25, p. 114042Costa, C.A., (2008) Class. Quantum Grav., 25, p. 184002Johnson, W.W., Merkowitz, S.M., (1993) Phys. Rev. Lett., 70, p. 2367Coccia, E., Lobo, J.A., Ortega, J.A., (1995) Phys. Rev. D, 52, p. 3735Thorne, K.S., (1978) Phys. Rev. Lett., 40, p. 667Tobar, M.E., Ivanov, E.N., Blair, D.G., (2000) Gen. Rel. Grav., 32, p. 1799De Waard, (2005) Class. Quantum Grav., 22, pp. S215Vinet, J.-Y., (2010) Research in Astron Astrophys., 10, p. 956Costa, C.A., Aguiar, O.D., Magalhães, N.S., (2004) Class. Quantum Grav., 21, pp. S827Forward, R.L., (1971) Gen. Rel. Grav., 2, p. 149Eardley, D.M., Lee, D.L., Lightman, A.P., Wagoner, R.V., Will, C.M., (1973) Phys. Rev. Lett., 30, p. 884Bianchi, M., Coccia, E., Colacino, C.N., Fafone, V., Fucito, F., (1996) Class. Quantum Grav., 13, p. 2865Andrade, L.A., (2009) Microwave and Optical Tech. Lett., 51, p. 1120Furtado, S.R., (2012), in preparationIvanov, E.N., Hartnett, J.G., Tobar, M.E., (2000) IEEE Trans. Ultrason., Ferroelect., Freq. Contr., 47, p. 1526Pimentel, G.L., (2008) J. Phys. Conf. Series, 122, p. 012028Aguiar, (2009) Int. J. Modern Phys. D, 18, p. 2317Furtado, S.R., (2009), Ph.D. Thesis at INPE, not publishedBraginsky, V.B., Vorontsov, Y.I., Thorne, K.S., (1980) Science, 209, p. 547Thorne, K.S., The Quantum Limit for Gravitational-Wave Detectors and Methods of Circumventing It (1979) Sources of Gravitational Waves, p. 49. , ed. L L Smarr, Cambridge University Press, Cambridge, US
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