2004 ASTRONOMY & ASTROPHYSICS - Indian Academy of Sciences

CHAPTER 8
Gravitation and
Particle Astrophysics
Particle Astrophysics, and certain aspects of
General Relativity and Gravitation, are two of the
frontier research areas with significant implications
for basic physics, as well as for astronomy and
astrophysics. In a few select subfields, Indian
groups have made significant impact and are
internationally competitive. Based on pragmatic
assessments, we perceive that the Indian scientific
community is well placed to make further
significant contributions in the future.
Before highlighting some of the current areas of
research, a brief overview of the work done in the
past is given below.
The General Theory of Relativity has been
pursued in India for more than sixty years. And
there have been a number of important
contributions. Going back to the 1940s and 50s,
one might mention the seminal discoveries by P.C.
Vaidya of the metric of a radiating spherical star
and the equation describing the Universe with
rotation and shear by A.K. Raychaudhuri. A special
feature of research in this area is that it was also
pursued at a number of university departments.
Traditionally, research in General Relativity has
centred around finding exact solutions to Einstein
field equations assuming different symmetry
conditions for the geometry or assuming different
sources for matter.
During the last thirty years or so, there have been
several important investigations pertaining to
black holes. These include
• The perturbations of black holes and the
study of their normal modes and quasinormal
modes.
• The effect of rotation and magnetic field on
the shape of the event horizon.
• Trajectories of charged particles around black
holes.
• Particle creation by black holes and Hawking
radiation.
• Models of neutron stars, strange stars and the
possibility of ultra-compact objects.
• The Penrose process for energy extraction
from black holes.
• Accretion disks and plasma processes around
black holes.
• Models of rapidly rotating neutron stars and
their oscillations.
• Gravitational lensing.
• Singularity theorems, gravitational collapse
and naked singularities.
Cosmology has been a popular subject in India,
both the mathematical aspects, as well as physical
cosmology. There have been several significant
contributions to cosmology and a few of them are
listed below.
• Pioneering suggestion that neutrinos with
finite rest mass might have important
cosmological consequences, including for the
formation of structures in the Universe.
• Cosmological effects of model theories of
quantum gravity.
• Large scale structure formation in the
Universe.
• Gravitational wave backgrounds in
inflationary models.
• Anisotropy of the cosmic microwave
background radiation.
• Topological defects in the Universe, etc.
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