9 research outputs found
Neutron Star Interiors: From Proto-Neutron Stars To Galactic Pulsars
Neutron stars are astrophysical laboratories to study extremely dense matter. The exact composition of the interior of a neutron star is yet unknown. However, recent observational and theoretical developments have provided crucial constraints on the properties of dense matter in neutron stars. In this thesis, we describe how we can use the astrophysical signals from neutron stars to measure their physical properties. We can use these measurements to determine the structure and composition of neutron star. We focus on two phases of the neutron star’s life and the astrophysical signals associated with it. First, we look at gravitational wave signals from core-collapse supernovae—the birthplace of neutron stars. We analyze the gravitational-wave signals obtained from three-dimensional simulations of core-collapse and calculate the detection prospects of these signals by the proposed next-generation detectors, such as Cosmic Explorer. We find that Cosmic Explorer can detect a supernova signal in the Milky Way galaxy. We analyze the first ∼ 10 ms of the gravitational-wave signal from core-collapse, where the signal is non-stochastic and primarily depends on the core rotation rate and its equation of state. We use data from numerical simulations of collapsing stars with rapidly rotating cores and develop a mapping between the physical parameters and the waveform morphology. We analyze the stochastic part of the signal, which is primarily generated due to the oscillations of the proto-neutron star. We develop a novel method to generate time-frequency spectrograms and we use them to measure the frequencies and energy associated with the quadrupolar f −mode oscillations of the proto-neutron star. Lastly, we determine the reproducibility of Riley et al. results, in which the authors analyze the X-ray data from NICER to measure the mass and radius of PSR J0030+0451 using X-ray pulse profile modeling. We find that using the data and software artifacts provided, we can not only reproduce their results but can extend them as well. Measuring the mass and radius of pulsar constrains its equation of state, and consequently its internal composition
Measuring the properties of mode oscillations of a protoneutron star by third generation gravitational-wave detectors
Core-collapse supernovae are among the astrophysical sources of gravitational
waves that could be detected by third-generation gravitational-wave detectors.
Here, we analyze the gravitational-wave strain signals from two- and
three-dimensional simulations of core-collapse supernovae generated using the
code F{\sc{ornax}}. A subset of the two-dimensional simulations has non-zero
core rotation at the core bounce. A dominant source of time changing quadrupole
moment is the fundamental mode ( mode) oscillation of the
proto-neutron star. From the time-frequency spectrogram of the
gravitational-wave strain we see that, starting ms after the core
bounce, most of the power lies within a narrow track that represents the
frequency evolution of the mode oscillations. The mode frequencies
obtained from linear perturbation analysis of the angle-averaged profile of the
protoneutron star corroborate what we observe in the spectrograms of the
gravitational-wave signal. We explore the measurability of the mode
frequency evolution of protoneutron star for a supernova signal observed in the
third-generation gravitational-wave detectors. Measurement of the frequency
evolution can reveal information about the masses, radii, and densities of the
proto-neutron stars. We find that if the third generation detectors observe a
supernova within 10 kpc, we can measure these frequencies to within 90\%
accuracy. We can also measure the energy emitted in the fundamental mode
using the spectrogram data of the strain signal. We find that the energy in the
mode can be measured to within 20\% error for signals observed by Cosmic
Explorer using simulations with successful explosion, assuming source distances
within 10 kpc.Comment: 17 pages, 11 figures, 2 table
Detection and characterization of spin-orbit resonances in the advanced gravitational wave detectors era
In this paper, we test the performance of templates in detection and
characterization of Spin-orbit resonant (SOR) binaries. We use precessing
SEOBNRv3 waveforms as well as {\it four} numerical relativity (NR) waveforms to
model GWs from SOR binaries and filter them through IMRPhenomD, SEOBNRv4
(non-precessing) and IMRPhenomPv2 (precessing) approximants. We find that
IMRPhenomD and SEOBNRv4 recover only of injections with fitting
factor (FF) higher than 0.97 (or 90\% of injections with ).However, using the sky-maxed statistic, IMRPhenomPv2 performs
magnificently better than their non-precessing counterparts with recovering
of the injections with FFs higher than 0.97. Interestingly, injections
with have higher FFs ( is the angle
between the components of the black hole spins in the plane orthogonal to the
orbital angular momentum) as compared to their and
generic counterparts. This implies that we will have a slight observation bias
towards SORs while using non-precessing templates for
searches. All template approximants are able to recover most of the injected NR
waveforms with FFs . For all the injections including NR, the error in
estimating chirp mass remains below with minimum error for resonant binaries. The symmetric mass ratio can be estimated
with errors below . The effective spin parameter is
measured with maximum absolute error of 0.13. The in-plane spin parameter
is mostly underestimated indicating that a precessing signal will be
recovered as a relatively less precessing signal. Based on our findings, we
conclude that we not only need improvements in waveform models towards
precession and non-quadrupole modes but also better search strategies for
precessing GW signals.Comment: 27 pages, 15 figures. Abstract shortened due to word limi
Detection and characterization of spin-orbit resonances in the advanced gravitational wave detectors era
Spin-orbit resonances have important astrophysical implications as the evolution and subsequent coalescence of supermassive black hole binaries in one of these configurations may lead to low recoil velocity of merger remnants. It has also been shown that black hole spins in comparable mass stellar-mass black hole binaries could preferentially lie in a resonant plane when their gravitational waves (GWs) enter the advanced LIGO frequency band [1]. Therefore, it is highly desirable to investigate the possibility of detection and subsequent characterization of such GW sources in the advanced detector era, which can, in turn, improve our perception of their high mass counterparts. The current detection pipelines involve only nonprecessing templates for compact binary searches whereas parameter estimation pipelines can afford to use approximate precessing templates. In this paper, we test the performance of these templates in detection and characterization of spin-orbit resonant binaries. We use fully precessing time-domain SEOBNRv3 waveforms as well as four numerical relativity (NR) waveforms to model GWs from spin-orbit resonant binaries and filter them through IMRPhenomD, SEOBNRv4 and IMRPhenomPv2 approximants. We find that the nonprecessing approximants IMRPhenomD and SEOBNRv4 recover only ∼70% of injections with fitting factor (FF) higher than 0.97 (or 90% of injections with FF>0.9). This loss in signal-to-noise ratio is mainly due to the missing physics in these approximants in terms of precession and nonquadrupole modes. However, if we use a new statistic, i.e., maximizing the matched filter output over the sky-location parameters as well, the precessing approximant IMRPhenomPv2 performs magnificently better than their nonprecessing counterparts with recovering 99% of the injections with FFs higher than 0.97. Interestingly, injections with Δϕ=180° have higher FFs (Δϕ is the angle between the components of the black hole spins in the plane orthogonal to the orbital angular momentum) as compared to their Δϕ=0° and generic counterparts. This is because Δϕ=180° binaries are not as strongly precessing as Δϕ=0° and generic binaries. This implies that we will have a slight observation bias towards Δϕ=180° and away from Δϕ=0° resonant binaries while using nonprecessing templates for searches. Moreover, all template approximants are able to recover most of the injected NR waveforms with FFs >0.95. For all the injections including NR, the systematic error in estimating chirp mass remains below <10% with minimum error for Δϕ=180° resonant binaries. The symmetric mass-ratio can be estimated with errors below 15%. The effective spin parameter χ_(eff) is measured with maximum absolute error of 0.13. The in-plane spin parameter χ_p is mostly underestimated indicating that a precessing signal will be recovered as a relatively less precessing signal. Based on our findings, we conclude that we not only need improvements in waveform models towards precession and nonquadrupole modes but also better search strategies for precessing GW signals
Characterizing Gravitational Wave Detector Networks: From A to Cosmic Explorer
Gravitational-wave observations by the Laser Interferometer
Gravitational-Wave Observatory (LIGO) and Virgo have provided us a new tool to
explore the universe on all scales from nuclear physics to the cosmos and have
the massive potential to further impact fundamental physics, astrophysics, and
cosmology for decades to come. In this paper we have studied the science
capabilities of a network of LIGO detectors when they reach their best possible
sensitivity, called A#, and a new generation of observatories that are factor
of 10 to 100 times more sensitive (depending on the frequency), in particular a
pair of L-shaped Cosmic Explorer observatories (one 40 km and one 20 km arm
length) in the US and the triangular Einstein Telescope with 10 km arms in
Europe. We use a set of science metrics derived from the top priorities of
several funding agencies to characterize the science capabilities of different
networks. The presence of one or two A# observatories in a network containing
two or one next generation observatories, respectively, will provide good
localization capabilities for facilitating multimessenger astronomy and
precision measurement of the Hubble parameter. A network of two Cosmic Explorer
observatories and the Einstein Telescope is critical for accomplishing all the
identified science metrics including the nuclear equation of state,
cosmological parameters, growth of black holes through cosmic history, and make
new discoveries such as the presence of dark matter within or around neutron
stars and black holes, continuous gravitational waves from rotating neutron
stars, transient signals from supernovae, and the production of stellar-mass
black holes in the early universe. For most metrics the triple network of next
generation terrestrial observatories are a factor 100 better than what can be
accomplished by a network of three A# observatories.Comment: 45 pages, 20 figure
Detection and characterization of spin-orbit resonances in the advanced gravitational wave detectors era
In this paper, we test the performance of templates in detection and characterization of Spin-orbit resonant (SOR) binaries. We use precessing SEOBNRv3 waveforms as well as {\it four} numerical relativity (NR) waveforms to model GWs from SOR binaries and filter them through IMRPhenomD, SEOBNRv4 (non-precessing) and IMRPhenomPv2 (precessing) approximants. We find that IMRPhenomD and SEOBNRv4 recover only of injections with fitting factor (FF) higher than 0.97 (or 90\% of injections with ).However, using the sky-maxed statistic, IMRPhenomPv2 performs magnificently better than their non-precessing counterparts with recovering of the injections with FFs higher than 0.97. Interestingly, injections with have higher FFs ( is the angle between the components of the black hole spins in the plane orthogonal to the orbital angular momentum) as compared to their and generic counterparts. This implies that we will have a slight observation bias towards SORs while using non-precessing templates for searches. All template approximants are able to recover most of the injected NR waveforms with FFs . For all the injections including NR, the error in estimating chirp mass remains below