Science case for the Einstein telescope Maggiore, Michele; Broeck, Chris Van Den; Bartolo, Nicola ...
Journal of cosmology and astroparticle physics,
03/2020, Letnik:
2020, Številka:
3
Journal Article
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The Einstein Telescope (ET), a proposed European ground-based gravitational-wave detector of third-generation, is an evolution of second-generation detectors such as Advanced LIGO, Advanced Virgo, ...and KAGRA which could be operating in the mid 2030s. ET will explore the universe with gravitational waves up to cosmological distances. We discuss its main scientific objectives and its potential for discoveries in astrophysics, cosmology and fundamental physics.
Because of its speed after training, machine learning is often envisaged as a solution to a manifold of the issues faced in gravitational-wave astronomy. Demonstrations have been given for various ...applications in gravitational-wave data analysis. In this Letter, we focus on a challenging problem faced by third-generation detectors: parameter inference for overlapping signals. Because of the high detection rate and increased duration of the signals, they will start to overlap, possibly making traditional parameter inference techniques difficult to use. Here, we show a proof-of-concept application of normalizing flows to perform parameter estimation on overlapped binary black hole systems.
ABSTRACT
Gravitational waves, like light, can be gravitationally lensed by massive astrophysical objects such as galaxies and galaxy clusters. Strong gravitational-wave lensing, forecasted at a ...reasonable rate in ground-based gravitational-wave detectors such as Advanced LIGO, Advanced Virgo, and KAGRA, produces multiple images separated in time by minutes to months. These images appear as repeated events in the detectors: gravitational-wave pairs, triplets, or quadruplets with identical frequency evolution originating from the same sky location. To search for these images, we need to, in principle, analyse all viable combinations of individual events present in the gravitational-wave catalogues. An increasingly pressing problem is that the number of candidate pairs that we need to analyse grows rapidly with the increasing number of single-event detections. At design sensitivity, one may have as many as $\mathcal {O}(10^5)$ event pairs to consider. To meet the ever-increasing computational requirements, we develop a fast and precise Bayesian methodology to analyse strongly lensed event pairs, enabling future searches. The methodology works by replacing the prior used in the analysis of one strongly lensed gravitational-wave image by the posterior of another image; the computation is then further sped up by a pre-computed lookup table. We demonstrate how the methodology can be applied to any number of lensed images, enabling fast studies of strongly lensed quadruplets.
Interpreting high-energy, astrophysical phenomena, such as supernova explosions or neutron-star collisions, requires a robust understanding of matter at supranuclear densities. However, our knowledge ...about dense matter explored in the cores of neutron stars remains limited. Fortunately, dense matter is not probed only in astrophysical observations, but also in terrestrial heavy-ion collision experiments. Here we use Bayesian inference to combine data from astrophysical multi-messenger observations of neutron stars
and from heavy-ion collisions of gold nuclei at relativistic energies
with microscopic nuclear theory calculations
to improve our understanding of dense matter. We find that the inclusion of heavy-ion collision data indicates an increase in the pressure in dense matter relative to previous analyses, shifting neutron-star radii towards larger values, consistent with recent observations by the Neutron Star Interior Composition Explorer mission
,
. Our findings show that constraints from heavy-ion collision experiments show a remarkable consistency with multi-messenger observations and provide complementary information on nuclear matter at intermediate densities. This work combines nuclear theory, nuclear experiment and astrophysical observations, and shows how joint analyses can shed light on the properties of neutron-rich supranuclear matter over the density range probed in neutron stars.
ABSTRACT
When travelling from their source to the observer, gravitational waves can get deflected by massive objects along their travel path. For a massive lens and a good source-lens alignment, the ...wave undergoes strong lensing, leading to several images with the same frequency evolution. These images are separated in time, magnified, and can undergo an overall phase shift. Searches for strongly lensed gravitational waves look for events with similar masses, spins, and sky location and linked through so-called lensing parameters. However, the agreement between these quantities can also happen by chance. To reduce the overlap between background and foreground, one can include lensing models. When doing realistic searches, one does not know which model is the correct one to be used. Using an incorrect model could lead to the non-detection of genuinely lensed events. In this work, we investigate how one can reduce the false alarm probability when searching for strongly lensed events. We focus on the impact of the addition of a model for the lens density profile and investigate the effect of potential errors in the modelling. We show that the risks of false alarm are high without the addition of a lens model. We also show that slight variations in the profile of the lens model are tolerable, but a model with an incorrect assumption about the underlying lens population causes significant errors in the identification process. We also suggest some strategies to improve confidence in the detection of strongly lensed gravitational waves.
The combined observation of gravitational and electromagnetic waves from the coalescence of two neutron stars marks the beginning of multimessenger astronomy with gravitational waves (GWs). The ...development of accurate gravitational waveform models is a crucial prerequisite to extract information about the properties of the binary system that generated a detected GW signal. In binary neutron star systems (BNS), tidal effects also need to be incorporated in the modeling for an accurate waveform representation. Building on previous work Phys. Rev. D 96, 121501 (2017), we explore the performance of inspiral-merger waveform models that are obtained by adding a numerical relativity (NR) based approximant for the tidal part of the phasing ( NRTidal ) to existing models for nonprecessing and precessing binary black hole systems, as implemented in the LSC Algorithm Library Suite. The resulting BNS waveforms are compared and contrasted to a set of target waveforms which we obtain by hybridizing NR waveforms (covering the last ∼ 10 orbits up to the merger and extending through the postmerger phase) with inspiral waveforms calculated from 30 Hz obtained with a state-of-the-art effective-one-body waveform model. While due to the construction procedure of the target waveforms, there is no error budget available over the full frequency range accessible by advanced GW detectors, the waveform set presents only an approximation of the real signal. We probe that the combination of the self-spin terms and of the NRTidal description is necessary to obtain minimal mismatches (≲ 0.01) and phase differences (≲ 1 rad) with respect to the target waveforms. We also discuss possible improvements and drawbacks of the NRTidal approximant in its current form.
The ability to directly detect gravitational waves has enabled us to empirically probe the nature of ultracompact relativistic objects. Several alternatives to the black holes of classical general ...relativity have been proposed which do not have a horizon, in which case a newly formed object (e.g., as a result of binary merger) may emit echoes: bursts of gravitational radiation with varying amplitude and duration, but arriving at regular time intervals. Unlike in previous template-based approaches, we present a morphology-independent search method to find echoes in the data from gravitational wave detectors, based on a decomposition of the signal in terms of generalized wavelets consisting of multiple sine-Gaussians. The ability of the method to discriminate between echoes and instrumental noise is assessed by inserting into the noise two different signals: a train of sine-Gaussians, and an echoing signal from an extreme mass-ratio inspiral of a particle into a Schwarzschild vacuum spacetime, with reflective boundary conditions close to the horizon. We find that both types of signals are detectable for plausible signal-to-noise ratios in existing detectors and their near-future upgrades. Finally, we show how the algorithm can provide a characterization of the echoes in terms of the time between successive bursts, and damping and widening from one echo to the next.
ABSTRACT
In the coming years, third-generation detectors such as Einstein Telescope and Cosmic Explorer will enter the network of ground-based gravitational-wave detectors. Their current design ...predicts a significantly improved sensitivity band with a lower minimum frequency than existing detectors. This, combined with the increased arm length, leads to two major effects: the detection of more signals and the detection of longer signals. Both will result in a large number of overlapping signals. It has been shown that such overlapping signals can lead to biases in the recovered parameters, which would adversely affect the science extracted from the observed binary merger signals. In this work, we analyse overlapping binary black hole coalescences with two methods to analyse multisignal observations: hierarchical subtraction and joint parameter estimation. We find that these methods enable a reliable parameter extraction in most cases and that joint parameter estimation is usually more precise but comes with higher computational costs.
Gravitational-wave observations of binary neutron star systems can provide information about the masses, spins, and structure of neutron stars. However, this requires accurate and computationally ...efficient waveform models that take ≲1 s to evaluate for use in Bayesian parameter estimation codes that perform 107–108 waveform evaluations. We present a surrogate model of a nonspinning effective-one-body waveform model with ℓ=2, 3, and 4 tidal multipole moments that reproduces waveforms of binary neutron star numerical simulations up to merger. The surrogate is built from compact sets of effective-one-body waveform amplitude and phase data that each form a reduced basis. We find that 12 amplitude and 7 phase basis elements are sufficient to reconstruct any binary neutron star waveform with a starting frequency of 10 Hz. The surrogate has maximum errors of 3.8% in amplitude (0.04% excluding the last 100M before merger) and 0.043 rad in phase. This leads to typical mismatches of 10−5−10−4 for Advanced LIGO depending on the component masses, with a worst case match of 7×10−4 when both stars have masses ≥2 M⊙. The version implemented in the LIGO Algorithm Library takes ∼0.07 s to evaluate for a starting frequency of 30 Hz and ∼0.8 s for a starting frequency of 10 Hz, resulting in a speed-up factor of O(103) relative to the original matlab code. This allows parameter estimation codes to run in days to weeks rather than years, and we demonstrate this with a nested sampling run that recovers the masses and tidal parameters of a simulated binary neutron star system.
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