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C. Sivaram

Publications and source records attributed to C. Sivaram.

At least 37 records · Page 2Linked to original sources
arXiv2010

Is the Binding Energy of Galaxies related to their Core Black Hole Mass?

Most of the large galaxies host a supermassive black hole, but their origin is still not well understood. In this paper we look at a possible connection between the gravitational binding energies of large galaxies etc. and the masses of their central black holes. Using this relation (between gravitational binding energy of the host structure and the black hole energy) we argue why globular clusters are unlikely to harbour large black holes and why dwarf galaxies, if they have to host black holes, should have observed mass to light ratios of ~100.

physics.gen-ph↗
arXiv2010

Thermal Gravitational Waves from Primordial Black Holes

Thermal gravitational waves can be generated in various sources such as, in the cores of stars, white dwarfs and neutron stars due to the fermion collisions in the dense degenerate Fermi gas. Such high frequency thermal gravitational waves can also be produced during the collisions in a gamma ray burst or during the final stages of the evaporation of primordial black holes. Here we estimate the thermal gravitational waves from primordial black holes and estimate the integrated energy of the gravitational wave emission over the entire volume of the universe and over Hubble time. We also estimate the gravitational wave flux from gamma ray bursts and jets.

physics.gen-ph↗
arXiv2010

Some Aspects of Rotational and Magnetic Energies for a Hierarchy of Celestial Objects

Celestial objects, from earth like planets to clusters of galaxies, possess angular momentum and magnetic fields. Here we compare the rotational and magnetic energies of a whole range of these celestial objects together with their gravitational self energies and find a number of interesting relationships. The celestial objects, due to their magnetic fields, also posses magnetic moments. The ratio of magnetic moments of these objects with the nuclear magnetic moments also exhibits interesting trends. We also compare their gyromagnetic ratio which appears to fall in a very narrow range for the entire hierarchy of objects. Here we try to understand the physical aspects implied by these observations and the origin of these properties in such a wide range of celestial objects, spanning some twenty orders in mass, magnetic field and other parameters.

astro-ph.CO↗
arXiv2009

Dark Energy, Inertia and Mach's Principle

Mach's Principle says that a particle's inertia is due to some interaction of that particle with all the other masses in the universe. Here we explore the possibility of the gravitational interaction energy of the background quantum vacuum energy playing the role of a global Higg's field (described by a varying cosmological constant) entirely contributing to the local inertial masses of particles in the spirit of Mach's principle.

astro-ph.CO↗
arXiv2008

Prospects for Observations of Transient UV Events with the TAUVEX UV Observatory

Transient events have posed special problems in astronomy because of the intrinsic difficulty of their detection, and a new class of observatories such as the Pan-STARRS and LSST are coming up specifically to observe these energetic events. In this paper we discuss the UV transient events from two specific sources, such as possible collisions in extrasolar planetary systems and M dwarf flares, to find the probability of their detection by space UV observatories, in particular, by the Tel Aviv University Explorer (TAUVEX). TAUVEX is an UV imaging experiment that will image large parts of the sky in the wavelength region between 120 and 350 nm. TAUVEX is a collaborative effort between the Indian Institute of Astrophysics (IIA) and Tel Aviv University, and is scheduled for an early-2009 launch with at least three years of operations. The scientific instrument has been fabricated at El-Op in Israel, with the satellite interfaces, launch and flight operations provided by the Indian Space Research Organization (ISRO). The ground-based software development is the responsibility of the IIA while other aspects of the mission are the joint responsibility of IIA and Tel Aviv University. TAUVEX Science Team (TST) have created a coherent observing program to address several Key Areas science objectives, one of them is a program to study short-scale UV transient events. We have estimated that in one year of TAUVEX observations we can expect about 90-350 short-scale transient events. Because we obtain real-time telemetry with TAUVEX, we will be able to catch transients early in their evolution and to alert other observatories. We also present a description of TAUVEX mission, including instrument design and its estimated performance.

astro-ph↗
arXiv2008

OJ 287: New Testing Ground for General Relativity and Beyond

The supermassive short period black hole binary OJ287 is discussed as a new precision testing ground for general relativity and alternate gravity theories. Like in the case of binary pulsars, the relativistic gravity effects are considerably larger than in the solar system. For instance the observed orbital precession is forty degrees per period. The gravitational radiation energy losses are comparable to typical blazar electromagnetic radiation emission and it is about ten orders larger than that of the binary pulsar with significant orbit shrinking already apparent in the light curves. This already tests Einstein gravity to a few percent for objects at cosmological distances. Constraints on alternate gravity theories as well as possible detection of long term effects of dark matter and dark energy on this system are described.

astro-ph↗
arXiv2008

Constraints on Gravitational Dipole Radiation from Pulsars

Recent suggestions for a modification of general relativity to provide an alternative approach to gravity in connection with the dark energy (matter) problem imply a long range vector component of the gravitational field. This could lead to emission of gravitational dipole emission from objects such as pulsars. Stringent observational limits on period changes of binary and millisecond pulsars and their consistency with general relativity impose severe limits on couplings of such forces. These bounds are tighter than those implied by lunar laser ranging experiments.

astro-ph↗
arXiv2008

Some Additional Bounds on the Photon Charge

We have arrived at tight constraints on the photon charge, giving comparable bounds, one based on the dominance by dark energy at the present epoch, and the other based on the requirement that early universe nucleosynthesis not be affected by any residual electrostatic energy due to any miniscule charge on the radiation photons in that era. Limits have also been arrived at from synchrotron and IC effects. We have also set limits on the charge based on the properties of black holes. The set of constraints arrived at in this paper are consistent with those predicted by other authors.

astro-ph↗
arXiv2007

Dark Energy may link the numbers of Rees

There is increasing evidence that the universe is dominated by dark energy of the type given by an invariant cosmological constant. Latest data also indicates that fundamental interaction couplings and particle masses have remained remarkably constant from the earliest epochs. It is natural to connect these two steady state features of the evolving universe, suggesting a role for the cosmic vacuum energy in fixing these interaction constants. Advances in high precision cosmology have revealed that dark matter of an unknown type constitutes about one-fourth of cosmic matter while baryons account for just four percent. These various cosmic parameters are enumerated by the six numbers of Rees. With the dark energy as a unifying link these

astro-ph↗
arXiv2007

Dark Matter, Dark Energy and Rotation Curves

Models for DM are invoked with various density distributions, to account for flat rotation curves of galaxies. The effect of DE on these profiles for large galaxies and clusters are also studied. The rotation curves are shown to dip at a particular distance, when the effect of DE became significant.

astro-ph↗
arXiv2007

Entropy of Stars, Black Holes and Dark Energy

When a star collapses to form a black hole, its entropy increases considerably, for a solar mass black hole, there is a factor of 1019 increase in entropy. This corresponds to a tremendous loss of information as only the total mass, angular momentum or electric charge (if any) of the matter going inside the horizon can be measured by an outside observer. Information about all other characteristics of the matter becomes irrelevant.

astro-ph↗
arXiv2007

Some Aspects of Intermediate mass black holes

There is a lot of current astrophysical evidence and interest in intermediate mass black holes, ranging from a few hundred to several thousand solar masses. The active galaxy M82 and the globular cluster in M31, for example, are known to host such objects. Here we discuss several aspects of intermediate mass black holes such as their expected luminosity, spectral nature of radiation, associated jets, etc. We also discuss possible scenarios for their formation including the effects of dynamical friction, gravitational radiation, etc. We also consider their formation in the early universe and also discuss the possibility of supermassive black holes forming from mergers of several intermediate mass black holes and compare the relevant time scales involved with other scenarios.

astro-ph↗
arXiv2007

Thermal gravitational waves

There is a lot of current interest in sources of gravitational waves and active ongoing projects to detect such radiation, such as the LIGO project. These are long wavelength, low frequency gravitational waves. LISA would be sensitive to much longer wavelengths and lower fluxes. However compact stellar objects can generate high frequency thermal gravitational radiation, which in the case of hot neutron stars can be high. Also white dwarfs and main-sequence stars can generate such radiation from plasma-Coulomb collisions. Again gamma ray bursts and relativistic jets could also be sources of such radiation. Terminal stages of evaporating black holes could also generate high frequency gravitational radiation. A comparative study is made of the thermal gravitational wave emission from all of the above sources, and the background flux is estimated. The earliest phases of the universe close to the Planck scale would also leave remnant thermal gravitational waves. The integrated thermal gravitational flux as the universe expands is also estimated and compared with that from all the discrete sources discussed above. Possible schemes to detect such sources of high frequency thermal gravitational radiation are discussed and the physical principles involved are elaborated.

astro-ph↗
arXiv2007

What is Special About the Planck Mass?

Planck introduced his famous units of mass, length and time a hundred years ago. The many interesting facets of the Planck mass and length are explored. The Planck mass ubiquitously occurs in astrophysics, cosmology, quantum gravity, string theory, etc. Current aspects of its implications for unification of fundamental interactions, energy dependence of coupling constants, dark energy, etc. are discussed.

gr-qc↗
arXiv2007

Phase Space Constraints on Neutrino Luminosities

While the importance of phase space constraints for gravitational clustering of neutrinos (which are fermions) is well recognized, the explicit use of such constraints to limit neutrino emission from ultra energetic sources has not been stressed. Special and general relativistic phase space constraints are shown to limit neutrino luminosities in compact sources in various situations.

astro-ph↗
arXiv2001

Torsion Gravity Effects on Charged-Particles and Neutron Interferometers

Torsion gravitational effects in the quantum interference of charged particles are investigated. The influence of axial torsion in the Schiff-Banhill effect (SB) inside a metallic shell is given. The effect of torsion on the surface of the earth on (SB) experiment is estimated. Torsion gravity effects on the Sagnac phase-shift of neutron interferometry are also computed.

gr-qc↗
arXiv2001

Cosmic repulsion in presence of matter

A basic problem that confronts the standard cosmological models is the problem of initial singularity characterised by infinite material density, infinite temperature and infinite spacetime curvature. The inevitable existence of such a phase of the universe may be considered to be one of the major drawbacks of Einstein's field equations. To some extent inflation models ameliorate this. In the present work we postulate that whenever matter (radiation) arises in flat spacetime, it introduces curvature and causes a repulsive interaction to develop. A modified energy momentum tensor is introduced towards this end, which invokes the temperature, entropy and a cosmic scalar field. This redefinition of the energy momentum distribution when applied to the early universe dynamics has the effect of producing a non-singular initial behaviour. the repulsive interaction introduces some features of an accelarating universe. In this model all cosmological parameters are mathematically well behaved. There is no flatness problem. Temperature at the beginning of this universe is 10^32 kelvin.

gr-qc↗