arXiv subjects

Samanwaya Mukherjee

Publications and source records attributed to Samanwaya Mukherjee.

6 recordsLinked to original sources

arXiv2026

Binary black holes in the heat of merger

A black hole binary approaching merger undergoes changes in its inspiral rate as energy and angular momentum are lost from the orbits into the horizons. This effect strengthens as the black holes come closer. We use numerical relativity data to model this so-called tidal heating in the strong gravity regime. We present a frequency-domain approximant for nonspinning black hole binaries that accounts for tidal heating effects up to the merger frequency. The approximant includes horizon parameters that characterize the nature of the compact objects. By applying this model to a binary black hole baseline that incorporates tidal heating, one can construct a more accurate point-particle waveform, one that is devoid of finite-size effects of the component objects. We also discuss its ramifications in modeling binary neutron star systems.

gr-qc↗

arXiv2026

Bose-Einstein Condensate Dark Matter in the Core of Neutron Stars: Implications for Gravitational-wave Observations

We investigate neutron stars admixed with dark matter (DM) in the form of a finite-temperature Bos-Einstein condensate (BEC) within a general relativistic two-fluid framework in which the nuclear and dark components interact only gravitationally. Using realistic nuclear matter equations of state (EOS), APR4, MPA1, and SLy, we construct equilibrium configurations and compute mas-radius relations, tidal Love numbers, and dimensionless tidal deformabilities. We quantify how the presence of a BEC dark component modifies the mas-$Λ$ relation relevant for gravitational wave observations, finding that increasing the DM mass fraction generically reduces the maximum mass, radius, and tidal deformability of neutron stars. By comparing theoretical mass-$Λ$ curves with EOS-insensitive posteriors from GW170817, we evaluate, in a conditional sense, the dark matter fractions that would align a given nuclear EOS with the observed tidal constraints; for example, under the assumption that APR4 describes nuclear matter and that the GW170817 components were dark-matter admixed neutron stars, our study favors dark matter fractions of order a few percent, whereas stiffer EOSs require larger fractions to achieve comparable agreement. This interpretation assumes that inspiral waveforms are adequately characterized by tidal deformability and should therefore be regarded as structural rather than a direct detection of dark matter. We also examine finite-temperature effects in the BEC sector and find that, for moderate dark matter fractions, temperature has a negligible impact on the stability and tidal properties of admixed configurations. Our results demonstrate how even modest DM admixtures can influence neutron star structure and tidal observables, highlighting the importance of considering non-standard matter components in multimessenger constraints on dense matter.

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arXiv2025

Tidal dissipation in binary neutron star inspirals from hyperon bulk viscosity: Phase modeling and parameter estimation bias

During the inspiral of a binary neutron star, viscous processes in the neutron star matter can damp out the tidal energy induced by its companion and convert it to thermal energy. This tidal dissipation/heating process introduces a net phase shift in the gravitational wave signal. In our recent work, we showed based on a Newtonian estimate that tidal dissipation from bulk viscosity originating from the non-leptonic weak interactions involving hyperons could have a detectable phase shift in the gravitational-wave (GW) signal in the next-generation GW detectors. Using simulated signals, we demonstrate that not accounting for this physical effect in waveform models can result in systematic biases in tidal deformability measurements of high-mass neutron star ($\geq 1.8M_{\odot}$) binary observations in next-generation GW detectors. By employing Newtonian orbital dynamics, we model this tidal dissipation induced dephasing as a phenomenological function of the characteristic velocity. We incorporate its effect in gravitational waveforms of equal-mass binary neutron stars. Those waveforms are used to perform a full Bayesian parameter estimation, which confirms that our model can alleviate possible biases in tidal deformability estimation. We also illustrate that the model can accurately measure the additional phase due to tidal dissipation in a $2M_{\odot}$ neutron star in observations with next-generation GW detectors and discuss its significance in extreme matter studies.

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arXiv2024

Phenomenological gravitational waveform model of binary black holes incorporating horizon fluxes

Subjected to the tidal field of its companion, each component of a coalescing black hole binary suffers a slow change in its mass (tidal heating) and spin (tidal torquing) during the inspiral and merger. This effect modifies the phase and amplitude of the gravitational waveform. Numerical relativity (NR) waveforms contain these effects inherently, whereas analytical approximants for the early inspiral phase have to include them manually in the energy balance equation. In this work, we construct a frequency-domain gravitational waveform model that incorporates this effect, by recalibrating the inspiral phase of the waveform model IMRPhenomD to incorporate the phase corrections for tidal heating. We also include corrections to the amplitude by adding them directly to the inspiral amplitude model of IMRPhenomD. We demonstrate that the inclusion of the corrections, especially in the phase, confers an overall improvement in the phase agreement between the analytical inspiral model (uncalibrated SEOBNRv2) and NR data. The model presented here is faithful, with less than $1\%$ mismatches against a set of hybrid waveforms (except for one outlier that barely breaches this limit). The recalibrated model shows mismatches of up to $\sim 14\%$ with IMRPhenomD for high mass ratios and spins. Amplitude corrections become less significant for higher mass ratios, whereas the phase corrections leave more impact -- suggesting that the former is practically irrelevant for gravitational wave data analysis in Advanced LIGO (aLIGO), Virgo and KAGRA. Comparing with a set of 219 numerical relativity waveforms, we find that the median of mismatches decreases by $\sim 4\%$ in aLIGO zero-detuned high power noise curve, and by $\sim 1.5\%$ with a flat noise curve. This implies a modest but notable improvement in waveform accuracy.

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arXiv2024

Characterizing the Properties and Constitution of Compact Objects in Gravitational-Wave Binaries

Astrophysical observations point toward strong evidence for the existence of black holes (BHs). Nevertheless, it is yet to be established or ruled out with confidence whether some exotic compact objects (ECOs), capable of mimicking black holes from an observational point of view, are indeed doing so. In classical General Relativity (GR), a horizon is the defining feature of a black hole, which prevents any event inside from causally affecting the outside Universe. The quest for distinguishing black holes from horizonless compact objects using gravitational wave (GW) signals from compact binary coalescences (CBCs) can be helped by utilizing the phenomenon of tidal heating (TH), which leaves its imprint on the binary waveforms through the horizon parameters. First, we study the measurabilities of these parameters within the inspiral regime. Then, to extend our investigation for heavier binaries, we construct an inspiral-merger-ringdown waveform by using post-Newtonian calculations for the inspiral and numerical relativity data for the merger-ringdown part that incorporates the effects of tidal heating of black holes in the phase and the amplitude. The new model shows improvements in waveform accuracy when compared to numerical relativity data. In the late inspiral phase when the compact objects are closer to each other, the effects of tidal heating are stronger, opening up the possibility of identifying the objects more precisely. We demonstrate, from numerical relativity data of binary black holes, how one can model tidal heating in the late inspiral regime and leverage this knowledge to test for horizonless compact objects mimicking black holes. These studies bear significance in determining the nature of compact objects having masses in the entire range that LIGO and future ground-based gravitational-wave detectors can detect.

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arXiv2022

Towards establishing the presence or absence of horizons in coalescing binaries of compact objects by using their gravitational wave signals

The quest for distinguishing black holes (BH) from horizonless compact objects using gravitational wave (GW) signals from coalescing compact binaries can be helped by utilizing the phenomenon of tidal heating (TH), which leaves its imprint on binary waveforms through the horizon parameters. We investigate the effects of TH on GWs to probe the observability of the horizon parameters, mainly using Fisher matrix analysis to determine the errors and covariances between them. The horizon parameters are defined as $H_1$ and $H_2$ for the two binary components, with $H_{1,2} \in [0,1]$, and combined with the component masses and spins to form two new parameters, $H_{\rm eff5}$ and $H_{\rm eff8}$, to minimize their covariances in parameter estimation studies. In this work, we add the phase contribution due to TH in terms of $H_{\rm eff5}$ and $H_{\rm eff8}$ to a post-Newtonian waveform and examine the variation of their measurement errors with the binary's total mass, mass ratio, luminosity distance, and component spins. Since the Fisher matrix approach works well for high signal-to-noise ratio, we focus mainly on third-generation (3G) GW detectors Einstein Telescope and Cosmic Explorer and use LIGO and Virgo for comparison. We find that the region in the total binary mass where measurements of $H_{\rm eff5}$ and $H_{\rm eff8}$ are most precise are $\sim 20 - 30M_\odot$ for LIGO-Virgo and $\sim 50 - 80M_\odot$ for 3G detectors. Higher component spins allow more precise measurements of $H_{\rm eff5}$ and $H_{\rm eff8}$. For a binary situated at 200 Mpc with component masses $12M_\odot$ and $18M_\odot$, equal spins $χ_1=χ_2=0.8$, and $H_{\rm eff5}=0.6$, $H_{\rm eff8}=12$, the 1-$σ$ errors in these two parameters are $\sim 0.01$ and $\sim 0.04$, respectively, in 3G detectors. We substantiate our results from Fisher studies with a set of Bayesian simulations.

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