Research | Sanika S. Khadkikar

GW190425: Classifying BNS vs BBH Mergers and Constraining Asymmetric Dark Matter

Thu, 01 Jan 2026 00:00:00 +0000

GW190425 was detected by LIGO and Virgo in April 2019 with a total mass substantially higher than any known galactic double neutron star system. This raised immediate questions about whether it was a binary neutron star or a binary black hole merger, and whether exotic physics might explain the anomaly.

This paper develops a Bayesian framework to classify compact binary mergers using only gravitational wave data and applies it to GW190425. We also show that the anomalous mass of GW190425 is consistent with neutron stars that harbor asymmetric dark matter cores, and we place the first constraints on dark matter nucleon interactions from a gravitational wave event.

Published in Physical Review D (2026)

Precise and Accurate Neutron Star Radius Measurements with Next-Generation Gravitational Wave Detectors

Wed, 01 Jan 2025 00:00:00 +0000

Next-generation gravitational wave detectors, Einstein Telescope and Cosmic Explorer, will observe thousands of binary neutron star mergers and offer unprecedented precision on neutron star parameters. But precision without accuracy is a problem. Systematic biases in waveform models, prior assumptions, and pipeline choices can lead to confident but wrong measurements.

This paper gives a comprehensive assessment of how accurately next-generation detectors can measure neutron star radii, identifying and quantifying the dominant sources of systematic error. We show that achieving sub-percent accuracy on the radius, a key target for constraining the equation of state, requires careful control of waveform systematics and prior choices, and we give practical recommendations for the O5 era and beyond.

Published in Physical Review D (2025)

Quasi-Stationary Sequences of Hyper-Massive Neutron Stars with Exotic Equations of State

Sat, 01 Jan 2022 00:00:00 +0000

When two neutron stars merge, the remnant can survive briefly as a rapidly rotating hyper-massive neutron star before collapsing into a black hole. How long it survives and what it looks like encodes information about the equation of state at densities far beyond anything accessible in a terrestrial experiment.

This paper constructs quasi-stationary equilibrium sequences of hyper-massive neutron stars using exotic equations of state that include strange quark matter, hyperons, and other non-nucleonic degrees of freedom. We map out how the remnant mass, angular momentum, and oscillation frequencies change with the underlying microphysics, giving a theoretical foundation for interpreting post-merger gravitational wave signals from next-generation detectors.

Published in Journal of Astrophysics and Astronomy (2022)

Maximum Mass of Compact Stars from Gravitational Wave Events with Finite-Temperature Equations of State

Fri, 01 Jan 2021 00:00:00 +0000

The maximum mass of a neutron star is one of the most fundamental quantities in nuclear astrophysics. It marks the boundary between a neutron star and a black hole, and places direct constraints on the stiffness of dense matter at extreme densities. Gravitational wave observations of binary neutron star mergers, particularly signals that show a post-merger collapse, give us a rare observational window onto this threshold.

This paper extends maximum mass constraints to finite temperature equations of state, which matter for the hot dense remnant formed immediately after a merger. Using GW170817 and its multi-messenger counterparts, we derive bounds on the maximum mass of both cold and hot neutron stars. We show that thermal effects can shift the inferred maximum mass by up to roughly ten percent and need to be accounted for in any equation of state analysis.

Published in Physical Review C (2021)