Christ Junior College

Bangalore, India

Christ Junior College

Bangalore, India
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Arun K.,Christ University | Arun K.,Christ Junior College | Gudennavar S.B.,Christ University | Prasad A.,Udaipur Solar Observatory | Sivaram C.,Indian Institute of Astrophysics
Advances in Space Research | Year: 2017

One of the unresolved questions currently in cosmology is that of the non-linear accelerated expansion of the universe. This has been attributed to the so called Dark Energy (DE). The accelerated expansion of the universe is deduced from measurements of Type Ia supernovae. Here we propose alternate models to account for the Type Ia supernovae measurements without invoking dark energy. © 2017 COSPAR.


Arun K.,Christ University | Arun K.,Christ Junior College | Gudennavar S.B.,Indian Institute of Astrophysics | Sivaram C.,Indian Institute of Astrophysics
Advances in Space Research | Year: 2016

The nature of dark matter (DM) and dark energy (DE) which is supposed to constitute about 95% of the energy density of the universe is still a mystery. There is no shortage of ideas regarding the nature of both. While some candidates for DM are clearly ruled out, there is still a plethora of viable particles that fit the bill. In the context of DE, while current observations favour a cosmological constant picture, there are other competing models that are equally likely. This paper reviews the different possible candidates for DM including exotic candidates and their possible detection. This review also covers the different models for DE and the possibility of unified models for DM and DE. Keeping in mind the negative results in some of the ongoing DM detection experiments, here we also review the possible alternatives to both DM and DE (such as MOND and modifications of general relativity) and possible means of observationally distinguishing between the alternatives. © 2017 COSPAR.


Sivaram C.,Indian Institute of Astrophysics | Kenath A.,Christ Junior College
Astrophysics and Space Science | Year: 2011

In this paper it is suggested that inclusion of mutual gravitational interactions among the particles in the early dense universe can lead to a 'pre-big bang' scenario, with particle masses greater than the Planck mass implying an accelerating phase of the universe, which then goes into the radiation phase when the masses fall below the Planck mass. The existence of towers of states of such massive particles (i. e. multiples of Planck mass) as implied in various unified theories, provides rapid acceleration in the early universe, similar to the usual inflation scenario, but here the expansion rate goes over 'smoothly' to the radiation dominated universe when temperature becomes lower than the Planck temperature. © 2011 Springer Science+Business Media B.V.


Sivaram C.,Indian Institute of Astrophysics | Arun K.,Christ Junior College
Astrophysics and Space Science | Year: 2012

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. © 2011 Springer Science+Business Media B.V.


Sivaram C.,Indian Institute of Astrophysics | Arun K.,Christ Junior College
Astrophysics and Space Science | Year: 2012

In a recent paper it was suggested that inclusion of mutual gravitational interactions can give a possible scenario for reversing gravitation collapse and averting a singular phase. We extend this idea to the still unsolved problem of matter collapsing beyond black hole event horizons. For a comoving observer there is no change in entropy as he goes through the horizon. Matter collapses to a minimum radius, and then can re-expand with the same entropy. It is shown that phase space inside a collapsing black hole is also invariant. © 2011 Springer Science+Business Media B.V.


Sivaram C.,Indian Institute of Astrophysics | Arun K.,Christ Junior College
Astrophysics and Space Science | Year: 2012

In recent papers we had developed a unified picture of black hole entropy and curvature which was shown to lead to Hawking radiation. It was shown that for any black hole mass, holography implies a phase space of just one quantum associated with the interior of the black hole. Here we study extremal rotating and charged black holes and obtain unique values for ratios of angular momentum to entropy, charge to entropy, etc. It turns out that these ratios can be expressed in terms of fundamental constants in nature, having analogies with other physical systems, like in condensed matter physics. © 2012 Springer Science+Business Media B.V.


Sivaram C.,Indian Institute of Astrophysics | Arun K.,Christ Junior College
Advances in High Energy Physics | Year: 2014

There is a lot of current astrophysical evidence and interest in intermediate mass black holes (IMBH), ranging from a few hundred to several thousand solar masses. The active galaxy M82 and the globular cluster G1 in M31, for example, are known to host such objects. Here, we discuss several aspects of IMBH such as their expected luminosity, spectral nature of radiation, and associated jets. We also discuss possible scenarios for their formation including the effects of dynamical friction, and gravitational radiation. We also consider their formation in the early universe and also discuss the possibility of supermassive black holes forming from mergers of several IMBH and compare the relevant time scales involved with other scenarios. © 2014 C. Sivaram and Kenath Arun.


Sivaram C.,Indian Institute of Astrophysics | Arun K.,Christ Junior College
Astrophysics and Space Science | Year: 2013

As is well known, black hole entropy is proportional to the area of the horizon suggesting a holographic principle wherein all degrees of freedom contributing to the entropy reside on the surface. In this note, we point out that large scale dark energy (such as a cosmological constant) constraining cosmic structures can imply a similar situation for the entropy of a hierarchy of such objects. © 2013 Springer Science+Business Media Dordrecht.


Sivaram C.,Indian Institute of Astrophysics | Kenath A.,Christ Junior College | Kiren O.V.,Christ Junior College
Astrophysics and Space Science | Year: 2014

Just forty years ago, Hawking wrote his famous paper on primordial black holes (PBH). There have been since innumerable discussions on the consequences of the existence of such exotic objects and ramifications of their properties. Here we suggest that PBH's in an ever expanding universe (as implied by dark energy domination, especially of a cosmological constant) could be the ultimate repository for long lived living systems. PBH's having solar surface temperatures would last 1032 years as a steady power source and should be considered in any discussion on exobiological life. © 2014 Springer Science+Business Media Dordrecht.


Sivaram C.,Indian Institute of Astrophysics | Arun K.,Christ Junior College
Astrophysics and Space Science | Year: 2011

Matter collapsing to a singularity in a gravitational field is still an intriguing question. Similar situation arises when discussing the very early universe or a universe recollapsing to a singularity. It was suggested that inclusion of mutual gravitational interactions among the collapsing particles can avert a singularity and give finite value for various physical quantities. We also discussed how inclusion of large dark energy term compensates for the net gravity. The discussion is taken further by including the effects of charge, magnetic fields and rotation. The role of large extra dimensions under the extreme initial conditions is discussed and possible connection with the cyclic brane theory is explored. We constrain various cosmic quantities like the net charge, number density of magnetic monopoles, primordial magnetic fields, size of the extra dimensions, etc. We are also able to arrive at the parameters governing the observed universe. © 2011 Springer Science+Business Media B.V.

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