Alladi Ramakrishnan Hall

White dwarf physics in Einstein’s gravity and its modification and magnetic field

Surajit Kalita

IISc, Bengaluru

Einstein’s theory of general relativity (GR) is an incredible theory to explain
various astrophysical phenomena and early universe cosmology. It provides an im-
mense understanding of the physics of various compact objects e.g. black holes,
neutron stars, white dwarfs, etc. However, some recent observations of cosmology
and also of compact objects question the complete validity of GR in the high density
regime. Moreover, a white dwarf having a binary partner, pulls matter out from
the companion star and beyond a certain mass, known as Chandrasekhar mass limit
(1.4M for a carbon-oxygen white dwarf), the white dwarf becomes unstable and
it burns out to produce type Ia supernova (SNIa). Nevertheless, some recent obser-
vations of SNeIa argue that the value of the Chandrasekhar mass limit has to be
violated. Such SNeIa are believed to be originating either from white dwarfs with
mass much less than the Chandrasekhar mass limit (0.5M), or much higher than
it (2.8M). In my talk, I will explain that these two classes of white dwarfs (sub-
and super-Chandrasekhar limiting mass white dwarfs) can easily be explained using
various forms of the f (R) gravity. I will show that central density of the white dwarf
is enough to explain sub- and super-Chandrasekhar limiting mass white dwarfs in
f (R) gravity, keeping the parameters of the model fixed. It is also to be noted that
all of these models are viable with respect to the solar system test. At last, I will
briefly talk about the generation of continuous gravitational wave from deformed
white dwarfs and these white dwarfs can be detected by the upcoming detectors e.g.
LISA, BBO, DECIGO, etc.