Browsing by Author "Chitre, S. M."

Now showing 1 - 17 of 17

3C 273 : A gravitationally lensed quasar?
(EDP Sciences, 1984-05-30) Chitre, S. M.; Narasimha, D.; Narlikar, J. V.; et al.
It is suggested that the abnormal brightness of the quasar 3C 273, coupled with the observations of superluminal motions in its radio core B as well as the misalignment of its VLBI jet with the optical jet, can be understood by postulating a faint spheroidal lensing galaxy located about halfway along the line of sight to the quasar. The lens model also helps to understand why the quasar is found slightly off-centre with respect to its nebulosity. The probability for such a lens system to arise for 3C 273 by chance is shown to be no less than that computed on the basis of the relativistic beaming hypothesis. Further tests of the lens model are discussed.
Applications of statistical techniques to the angular size-flux density relation for extraglactic radio sources
(Willy-Blackwell, 1977-01-14) Narlikar, J. V.; Chitre, S. M.
The data on the angular sizes (theta) and flux densities (S) of extragalactic radio sources selected from two surveys are subjected to two independent statistical tests in order to determine whether the data warrant the conclusion that the universe is evolving. The nature of the observed scatter in the (theta, S) relation is examined, and a minimum chi-squared test is used to compare the observed (theta, S) plot with three theoretical models (one evolutionary and two nonevolutionary). A median test is then applied to compare the median angular sizes of two source samples in a narrow range of flux density. The results obtained indicate that due to the existing large scatter in the (theta, S) data, it is not possible to distinguish clearly between the evolutionary and the nonevolutionary models.
Astrophysical applications of the gravitational searchlight
(Plenum Publishing Corporation, 1976-01-15) Chitre, S. M.; Narlikar, J. V.
The astrophysical consequences of the blue-shifted radiation emitted in the forward direc- tion by a source moving in an equatorial orbit with radius slightly in excess of 1.5 times the Schwarzschild radius of a highly collapsed central object are examined with special reference to quasistellar objects.
Blueshift and spectral features of the gravitational searchlight
(Plenum Publishing Corporation, 1975-01-17) Chitre, S. M.; Narlikar, J. V.; Kapoor, R. C.
It is shown that a photon emitted in the forward direc- tion by a charged particle moving in an equatorial cir- cular orbit centred on a highly collapsed mass M, the radius being slightly in excess of one and a half times the Schwarzschild radius, is strongly blueshifted when it arrives at a distant receiver. A ring shaped emit- ting region composed of such orbiting particles has a power law spectrum of the form d~/~ as seen by a distant stationary observer.
Bounds on vacuum energy density in a general cosmological scenario
(Elsevier Science Publishers, 1987-02-09) Joshi, P. S.; Padmanabhan, T.; Chitre, S. M.
General limits on the cosmological constant (or equivalently the vacuum energy density) are derived for an inflationary universe. This is accomplished under the general assumption of global hyperbolicity and without the use of any special properties like spherical symmetry or homogeneity ofthe underlying spacetime. Aclear upper limit of 1/3 is obtained for the vacuum energy density parameterQ~,while the lower limit is found to depend on the age of the oldest object in the universe.
Effect of intergalactic dust on the measurement of the cosmological deceleration parameter qo
(Indian Academy of Sciences, 1976-01-11) Chitre, S. M.; Narlikar, J. V.
In a recent attempt to explain the cosmic microwave background without the big bang, a thermalization mechanism involving intergalactic whisker grains of graphite was proposed. The effect of absorption by the intergalactic medium in general, and of the above type in particular, on the measurement of the deceleration parameter q0 of the expanding universe is discussed. Its effect is shown to be comparable in magnitude but opposite to that of the luminosity evolution in galaxies. A consequential selection effect is also discussed.
Faster-than-light motion in quasars
(Indian Academy of Sciences, 1984-07-27) Narlikar, J. V.; Chitre, S. M.
Over the past fifteen years, observations of some quasars with the techniques of very-long-baseline interferometry have shown that the angular separation between pairs of radio-emitting regions in their cores is increasing year after year. If the quasars are indeed as far away as implied by Hubble’s law, then these angular motions translate into linear speeds several times the speed of light. Several theoretical scenarios have been proposed to show that the observed motions are illusory. The leading contender in this field—the relativistic beam model—and an alternative offered by the concept of a gravitational screen are described and compared in the light of recent observational data.
Gravitational screens and superluminal separation in quasars
(American Astronomical Society, 1980-01-15) Chitre, S. M.; Narlikar, J. V.
The differential bending of radio waves by a suitably placed 'gravitational screen' such as an intervening galaxy can lead to large magnification of the separation velocity of the components in the nuclear region of a quasar. It is suggested that the apparent superluminal separation of such components observed in some quasars by the VLBI techniques could be due to velocity magnifications of this type. The astrophysical feasibility of this explanation is critically examined, and an optical search for objects of large mass-to-light ratio en route to quasars showing superluminal separation is advocated.
Gravitational searchlight and its astrophysical applications
(Nature Publishing Group, 1974-12-06) Chitre, S. M.; Narlikar, J. V.; Kapoor, R. C.
Gravitational searchlight effect
(Astronomical Society of India, 1975-01-11) Chitre, S. M.; Narlikar, J. V.; Kapoor, R. C.
Inconstant Sun: IUCAA Colloquium
(2011-09-20) Chitre, S. M.
Is gravitational lensing a local phenomenon caused by Pop - III objects?
(Gordon and Breach Science Publishers, 1986-01-31) Padmanabhan, T.; Chitre, S. M.
Neutral currents and the cooling of neutron stars
(Kluwer Academic Publishers, 1975-01-06) Chitre, S. M.; Narlikar, J. V.; Ramadurai, S.
Although the neutrino cooling rate by purely leptonic processes is altered by the neutral currents, the overall cooling of model neutron stars is shown to remain practically unaffected.
On the apparent superluminal separation of radio sources components
(Willy-Blackwell, 1979-01-13) Chitre, S. M.; Narlikar, J. V.
Temperature fluctuations of cosmic microwave background induced by gravitational lensing
(Elsevier Science Publishers, 1986-06-26) Chitre, S. M.; Narlikar, J. V.; Padmanabhan, T.
Temperature fluctuations of cosmic microwave background induced by gravitational lensing
(Elsevier Science Publishers, 1986-08-25) Chitre, S. M.; Narlikar, J. V.; Padmanabhan, T.
Adopting the accepted interpretation of the cosmic microwave background (CMBR) as a relic of the early hot universe we show that any angular intensity variations existing in the background at the "last scattering surface" at the redshift of ~10³ will induce bright fluctuations through gravitational lensing by intervening masses. The resulting temperature variations ΔT are estimated for gravitating masses like distant galaxies (z ~1) and local dark objects (e.g. population III stars) in our own Galaxy. It is found that the value of ΔT/T produced by the above mechanisms further constrains the theories of galaxy formation. The calculation also limits the amount of matter present in the form of population III objects in the galaxy.
Viscous universes
(Elsevier Science Publishers, 1987-03-23) Padmanabhan, T.; Chitre, S. M.
The effect of bulk viscosity on the evolution of the universe at large is investigated. It is demonstrated that bulk viscosity can lead to inflation-like solutions.