Stability of Exotic Compact Objects and Environmental Effects

Despite being successful in the weak field regime, the validity
of general relativity remains elusive in the strong field regime. Many
problems occur when trying to unify general relativity with quantum theory
in a self-consistent manner. Moreover, it is speculated that quantum
theory should modify black hole singularity. Recent GW astronomy has
opened the door to test general relativity in the strong field regime of
black holes, mainly the merger of binary black holes. The observed
ringdown waveform of the merger remnant is consistent with GR prediction.
However, several research papers have shown that any horizonless compact
object with a photon sphere can also mimic such a waveform. Interestingly
enough, it is known that such black hole alternatives can cure some of
GR's drawbacks. However, they are known to violate some energy conditions
or are formed beyond standard model fields. At this point, whether they
are stable under linear perturbations naturally comes to mind. In this
talk, I will focus on wormholes as an ECO. Under some special situations,
it is found by Kar-Lahiri-Sengupta that wormholes on the brane do not
require any exotic matter to sustain them. Here I will discuss the
perturbation of this wormhole under known bosonic perturbations. In the
next part of the talk, I will model the Damour-Solodukhin wormhole
residing inside the galactic halo and discuss the effect of dark matter on
it's stability. Finally, we will model a star like ECO by putting a
partially reflecting surface near the location of the would-be horizon.
Considering plasma accretion around this ECO spacetime, we have studied
the propagation of electromagnetic waves through plasma. I will discuss
interesting phenomenology regarding this perturbation scheme.