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Debarati Chatterjee

Publications and source records attributed to Debarati Chatterjee.

At least 37 records · Page 2Linked to original sources

Communicating the gravitational-wave discoveries of the LIGO-Virgo-KAGRA Collaboration

The LIGO-Virgo-KAGRA (LVK) Collaboration has made breakthrough discoveries in gravitational-wave astronomy, a new field that provides a different means of observing our Universe. Gravitational-wave discoveries are possible thanks to the work of thousands of people from across the globe working together. In this article, we discuss the range of engagement activities used to communicate LVK gravitational-wave discoveries and the stories of the people behind the science, using the activities surrounding the release of the third Gravitational-Wave Transient Catalog as a case study.

astro-ph.IM↗

Effects of Dark Matter on $f$-mode oscillations of Neutron Stars

The effect of dark matter (DM) on $f$-mode oscillations in DM admixed neutron stars (NSs) is investigated in a comprehensive analysis with particular attention to the role of the nuclear equation of state. Hadronic matter is modeled by the relativistic mean field model and the DM model is based on the neutron decay anomaly. The non-radial $f$-mode oscillations for such DM admixed NS are studied in a full general relativistic framework. We investigate the impact of DM, DM self-interaction, and DM fraction on the $f$-mode characteristics. We derive relations encoding the effect of DM on $f$-mode parameters. We then perform a systematic study by varying all the model parameters within their known uncertainty range and obtain a universal relation for the DM fraction based on the total mass of the star and DM self-interaction strength. We also perform a correlation study among model parameters, NS observables, in particular, $f$-mode parameters. Finally, we check the $f$-mode universal relations (URs) for the case of DM admixed NSs and demonstrate the existence of a degeneracy between purely hadronic NSs and DM admixed NSs.

gr-qc↗

Theoretical and Experimental Constraints for the Equation of State of Dense and Hot Matter

This review aims at providing an extensive discussion of modern constraints relevant for dense and hot strongly interacting matter. It includes theoretical first-principle results from lattice and perturbative QCD, as well as chiral effective field theory results. From the experimental side, it includes heavy-ion collision and low-energy nuclear physics results, as well as observations from neutron stars and their mergers. The validity of different constraints, concerning specific conditions and ranges of applicability, is also provided.

nucl-th↗

Probing hadron-quark phase transition in twin stars using $f$-modes

Although it is conjectured that a phase transition from hadronic to deconfined quark matter in the ultrahigh-density environment of Neutron Stars (NS), the nature of phase transition remains an unresolved mystery. Furthermore, recent efforts reveal that the finite surface tension effects can lead to a mixed phase with different geometric shapes (so-called "pasta" phases), leading to a smooth phase transition from hadronic to quark matter in the NS interior. Depending on whether there is a strong or a pasta-induced smooth first-order phase transition, one may expect a third family of stable, compact stars or "twin stars" to appear, with the same mass but different radii compared to NSs. The possibility of identifying twin stars using astrophysical observations has been a subject of interest. This study investigates the potential of probing the nature of the hadron-quark phase transition through future gravitational wave (GW) detections from fundamental ($f$-) mode oscillations in Neutron Stars. Using a newly developed model that parametrizes the hadron-quark phase transition with ``pasta phases," we calculate $f$-mode characteristics within a full general relativistic framework. We then use Universal Relations in GW asteroseismology to derive stellar properties from the detected mode parameters. Our findings suggest that detecting GWs from $f$-modes with third-generation GW detectors offers a promising scenario for the existence of twin stars. However, we also estimate various uncertainties in determining the mode parameters and conclude that these uncertainties make it more challenging to identify the nature of the hadron-quark phase transition.

nucl-th↗

Tidal heating as a direct probe of strangeness inside neutron stars

It has been discussed whether viscous processes in neutron star matter during a binary inspiral can damp out the tidal energy induced by the companion and heat up the star. Earlier investigations concluded that this tidal heating is negligible for normal neutron star matter. In this work, we suggest a novel effect of tidal heating involving strange matter in the neutron star interior, that can significantly heat up the star, and is potentially observable by current and future gravitational wave detectors. We propose that this could serve as a direct probe of strangeness in neutron stars.

gr-qc↗

Can the second time-derivative of the orbital frequency of binary pulsars be used for testing general relativity?

With precision pulsar timing, measured values of a large set of pulsar parameters are obtainable. For some of those parameters, such as the time-derivatives of spin or orbital periods (in the case of binary pulsars), the measured values are not the intrinsic values of the parameters as they contain contributions from the dynamical effects. In the case of orbital period derivatives, the intrinsic values are essentially the general relativistic results. Pulsar timing solution also provides measurement of higher time-derivatives of orbital frequency for some pulsars. We specifically focus on the second time-derivative of the orbital frequency to explore its application in testing general relativity. In this work, we have provided a formalism to estimate the general relativistic contribution to the second derivative of the orbital frequency. We have calculated the dynamical effect contributions as well as the general relativistic contributions to the second time-derivative of the orbital period for real as well as synthetic pulsars. We find that the general relativistic contribution to the second time-derivative of the orbital period is negligibly small compared to the observed values of the real pulsars.

gr-qc↗

Cost of inferred nuclear parameters towards the f-mode dynamical tide in binary neutron stars

Gravitational Wave (GW) observations from Neutron Stars (NS) in a binary system provide an excellent scenario to constrain the nuclear parameters. The investigation of Pratten et al. (2022) has shown that the ignorance of f-mode dynamical tidal correction in the GW waveform model of the binary neutron star (BNS) system can lead to substantial bias in the measurement of NS properties and NS equations of state (EOS). In this work, we investigate the bias in the nuclear parameters resulting from the ignorance of dynamical tidal correction. In addition, this work demonstrates the sensitivity of the nuclear parameters and the estimated constraints on them from future GW observations. We infer the nuclear parameters from GW observations by describing the NS matter within the relativistic mean field model. For a population of GW events, we notice that the ignorance of dynamical tide predicts a lower median for nucleon effective mass ($m^*$) by $\sim6\%$ compared to the scenario when dynamical tidal correction is considered. Whereas at a 90\% credible interval(CI), $m^*$ gets constrained up to $\sim 5\%$ and $\sim 3\%$ in A+ (the LIGO-Virgo detectors with a sensitivity of 5th observing run) and Cosmic Explorer (CE) respectively. We also discuss the resulting constraints on all other nuclear parameters, including compressibility, symmetry energy, and slope of symmetry energy, considering an ensemble of GW events. We do not notice any significant impact in analyzing nuclear parameters other than $m^*$ due to the ignorance of f-mode dynamical tides.

gr-qc↗

Multi-physics constraints at different densities to probe nuclear symmetry energy in hyperonic neutron stars

The appearance of strangeness in the form of hyperons within the inner core of neutron stars is expected to affect its detectable properties such as its global structure or gravitational wave emission. In this work, we explore the parameter space of hyperonic stars within the framework of the Relativistic Mean Field model allowed by present uncertainties in state-of-the-art nuclear and hypernuclear experimental data. We impose multi-physics constraints at different density regimes to restrict the parameter space: Chiral effective field theory, heavy-ion collision data as well as multi-messenger astrophysical observations of neutron stars. We investigate possible correlations between empirical nuclear and hypernuclear parameters, particularly the symmetry energy and its slope, with observable properties of neutron stars. We do not find a correlation for the hyperon parameters and the astrophysical data. However, the inclusion of hyperons generates a tension between the astrophysical and heavy ion data constraining considerable the available parameter space.

astro-ph.HE↗

Imposing multi-physics constraints at different densities on the Neutron Star Equation of State

Neutron star matter spans a wide range of densities, from that of nuclei at the surface to exceeding several times normal nuclear matter density in the core. While terrestrial experiments, such as nuclear or heavy-ion collision experiments, provide clues about the behaviour of dense nuclear matter, one must resort to theoretical models of neutron star matter to extrapolate to higher density and finite neutron/proton asymmetry relevant for neutron stars. In this work, we explore the parameter space within the framework of the Relativistic Mean Field model allowed by present uncertainties compatible with state-of-the-art experimental data. We apply a cut-off filter scheme to constrain the parameter space using multi-physics constraints at different density regimes: chiral effective field theory, nuclear and heavy-ion collision data as well as multi-messenger astrophysical observations of neutron stars. Using the results of the study, we investigate possible correlations between nuclear and astrophysical observables.

astro-ph.HE↗

R-modes as a New Probe of Dark Matter in Neutron Stars

In this work, we perform the first systematic investigation of effects of the presence of dark matter on $r$-mode oscillations in neutron stars (NSs). Using a self-interacting dark matter (DM) model based on the neutron decay anomaly and a hadronic model obtained from the posterior distribution of a recent Bayesian analysis, we impose constraints on the DM self-interaction strength using recent multimessenger astrophysical observations. We also put new constraints on the DM fraction for this model of DM. The constrained DM interaction strength is then used to estimate DM self-interaction cross section and shear viscosity resulting from DM, which is found to be several orders of magnitude smaller than shear viscosity due to hadronic matter. Assuming chemical equilibrium among DM fermions and neutrons, we estimate the bulk viscosity resulting from the dark decay of neutrons considering different scenarios for the temperature dependence of the reaction rate and investigate the effect on the $r$-mode instability window. We conclude that DM shear and bulk viscosity may significantly modify the $r$-mode instability window compared with the minimal hadronic viscosities, depending on the temperature dependence of the process. We also found that for the window to be compatible with the X-ray and pulsar observational data, the rate for the dark decay process must be fast.

astro-ph.HE↗

Role of vector self-interaction in Neutron Star properties

Previous studies have claimed that there exist correlations among certain nuclear saturation parameters and neutron star observables, such as the slope of the symmetry energy and the radius of a $1.4M_{\odot}$ neutron star. However, it is not clear whether such correlations are physical or spurious, as they are not observed universally for all equation of state models. In this work, we probe the role of vector self-interaction within the framework of the Relativistic Mean Field model and its role in governing the observable stellar properties and their correlations with nuclear parameters. We confirm that the effect of this term is not only to control the high density properties of the equation of state but also to govern such correlations. We also impose a limit on the maximum strength of the vector self-interaction using recent astrophysical data.

nucl-th↗

Prospects of identifying the presence of Strange Stars using Gravitational Waves from binary systems

The existence of self-bound strange stars is a long-standing mystery in astrophysics. Future astrophysical data, even with improved precision, may not allow us to discriminate them from neutron stars, given the uncertainties in observational and theoretical modeling. In this work, we propose a unique strategy to distinguish strange stars from neutron stars using gravitational waves from binary compact star systems. We demonstrate that empirical relations connecting f-mode frequencies with tidal deformation are distinct for the two classes of compact objects, irrespective of their equations of state. Therefore simultaneous measurement of f-mode frequency and tidal deformability from the inspiral phase of compact binary mergers with the next-generation detectors can provide smoking gun evidence for the presence of strange stars. This would have crucial implications not only in gravitational wave physics but multidisciplinary fields such as nuclear and high energy physics.

gr-qc↗

Improving the spin-down limits of the continuous gravitational waves emitted from rotating triaxial pulsars

The spin-down limit of the continuous gravitational wave strain from pulsars assumed to be triaxial stars rotating about a principal moment of inertia axis depends upon the value of the intrinsic spin frequency derivative of the pulsar, among other parameters. In order to get more accurate intrinsic spin frequency derivative values, dynamical effects contributing to the measured spin frequency derivative values must be estimated via more realistic approaches. In this work, we calculated improved values for the spin-down limit of the continuous gravitational wave strain (assuming that pulsars are triaxial stars rotating about a principal moment of inertia axis) for a set of 237 pulsars for which a targeted search for continuous gravitational waves was recently carried out by the LIGO-Virgo-KAGRA (LVK) Collaboration. We used `GalDynPsr', a Python-based public package, to calculate more realistic values for the intrinsic spin frequency derivatives and, consequently, we get more realistic values of the spin-down limit. The realistic values that we obtain for the intrinsic spin frequency derivatives can also provide a valuable contribution to improving the sensitivity of searches for continuous gravitational waves from known pulsars.

astro-ph.HE↗

Constraining nuclear parameters using Gravitational waves from f-mode Oscillations in Neutron Stars

Gravitational waves (GW) emanating from unstable quasi-normal modes in Neutron Stars (NS) could be accessible with the improved sensitivity of the current GW detectors or with the next-generation GW detectors and, therefore, can be employed to study the NS interior. Assuming f-mode excitation in isolated pulsars with typical energy of pulsar glitches and considering potential f-mode GW candidates for A+ (upgraded LIGO detectors operating at 5th observation run design sensitivity) and Einstein Telescope (ET), we demonstrate the inverse problem of NS asteroseismology within a Bayesian formalism to constrain the nuclear parameters and NS Equation of State (EOS). We describe the NS interior within relativistic mean field formalism. Taking the example of glitching pulsars, we find that for a single event in A+ and ET, among the nuclear parameters, the nucleon effective mass ($m^*$) within 90\% credible interval (CI) can be restricted within $10\%$ and $5\%$, respectively. At the same time, the incompressibility ($K$) and the slope of the symmetry energy ($L$) are only loosely constrained. Considering multiple (10) events in A+ and ET, all the nuclear parameters are well constrained, especially $m^*$, which can be constrained to 3\% and 2\% in A+ and ET, respectively. Uncertainty in the observables of a $1.4M_{\odot}$ NS such as radius ($R_{1.4M_{\odot}}$), f-mode frequency ($f_{1.4M_{\odot}}$), damping time ($τ_{1.4M_{\odot}}$) and a few EOS properties including squared speed of sound ($c_s^2$) are also estimated.

astro-ph.HE↗

Impact of updated Multipole Love numbers and f-Love Universal Relations in the context of Binary Neutron Stars

Neutron star (NS) equation of state (EoS) insensitive relations or universal relations (UR) involving neutron star bulk properties play a crucial role in gravitational-wave astronomy. Considering a wide range of equations of state originating from (i) phenomenological relativistic mean field models, (ii) realistic EoS models based on different physical motivations, and (iii) polytropic EoSs described by spectral decomposition method, we update the EoS-insensitive relations involving NS tidal deformability (Multipole Love relation) and the UR between f-mode frequency and tidal deformability (f-Love relation). We analyze the binary neutron star (BNS) event GW170817 using the frequency domain TaylorF2 waveform model with updated universal relations and find that the additional contribution of the octupolar electric tidal parameter and quadrupolar magnetic tidal parameter or the change of multipole Love relation has no significant impact on the inferred NS properties. However, adding the f-mode dynamical phase lowers the 90% upper bound on $\tildeΛ$ by 16-20% as well as lowers the upper bound of NSs radii by $\sim$500m. The combined URs (multipole Love and f-Love) developed in this work predict a higher median (also a higher 90% upper bound) for $\tildeΛ$ by 6% and also predict higher radii for the binary components of GW170817 by 200-300m compared to the URs used previously in the literature. We further perform injection and recovery studies on simulated events with different EoSs in $\rm A+$ detector configuration as well as with third generation (3G) Einstein telescope. In agreement with the literature, we find that neglecting f-mode dynamical tides can significantly bias the inferred NS properties, especially for low mass NSs. However, we also find that the impact of the URs is within statistical errors.

astro-ph.HE↗

g-mode Oscillations in Neutron Stars with Hyperons

A common alternative to the standard assumption of nucleonic composition of matter in the interior of a neutron star is to include strange baryons, particularly hyperons. Any change in composition of the neutron star core has an effect on g-mode oscillations of neutron stars, through the compositional dependence of the equilibrium and adiabatic sound speeds. We study the core g-modes of a neutron star contaning hyperons, using a variety of relativistic mean field models of dense matter that satisfy observational constraints on global properties of neutron stars. Our selected models predict a sharp rise in the g-mode frequencies upon the onset of strange baryons. Should g-modes be observed in the near future, their frequency could be used to test the presence of hyperonic matter in the core of neutron stars.

nucl-th↗

Constraining the equation of state of hybrid stars using recent information from multidisciplinary physics

At the ultra-high densities existing in the core of neutron stars, it is expected that a phase transition from baryonic to deconfined quark matter may occur. Such a phase transition would affect the underlying equation of state (EoS) as well as the observable astrophysical properties of neutron stars. Comparison of EoS model predictions with astronomical data from multi-messenger signals then provides us an opportunity to probe the behaviour of dense matter. In this work, we restrict the allowed parameter space of EoS models in neutron stars for both nucleonic (relativistic mean field model) and quark matter (bag model) sectors by imposing state-of-the-art constraints from nuclear calculations, multi-messenger astrophysical data and perturbative QCD (pQCD). We systematically investigate the effect of each constraint on the parameter space of uncertainties using a cut-off filter scheme, as well as the correlations among the parameters and with neutron star astrophysical observables. Using the constraints, we obtain limits for maximum NS mass, maximum central density, as well as for NS radii and tidal deformability. Although pQCD constraints are only effective at very high densities, they significantly reduce the parameter space of the quark model. We also conclude that astrophysical data supports high values of the bag parameter B and disfavors the existence of a pure quark matter core in hybrid stars.

astro-ph.HE↗

Relativistic correction to the r-mode frequency in light of multi-messenger constraints

R-mode oscillations of rotating neutron stars are promising candidates for continuous gravitational wave (GW) observations. The r-mode frequencies for slowly rotating Newtonian stars are well-known and independent of the equation of state (EOS) but for neutron stars, several mechanisms can alter the r-mode frequency of which the relativistic correction is dominant and relevant for most of the neutron stars. The most sensitive searches for continuous GWs are those for known pulsars for which GW frequencies are in targeted narrow frequency bands of few Hz. In this study, we investigate the effect of several state-of-the-art multi-messenger constraints on the r-mode frequency for relativistic, slowly rotating, barotropic stars. Imposing these recent constraints on the EOS, we find that the r-mode frequency range is slightly higher from the previous study and the narrow band frequency range can increase upto 8-25% for the most promising candidate PSR J0537-6910 depending on the range of compactness. We also derive universal relations between r-mode frequency and dimensionless tidal deformability which can be used to estimate the dynamical tide of the r-mode resonant excitation during the inspiral signal. These results can be used to construct the parameter space for r-mode searches in gravitational wave data and also constrain the nuclear equation of state following a successful r-mode detection.

gr-qc↗