Neutron Star Mergers

When two neutron stars revolve around each other, they emit gravitational waves which drives them – initially very subtly but in the end very violently – towards a collision. In such a collision, neutron star matter gets ejected into space where it forms heavy elements via the “rapid-neutron capture process”. The freshly synthesized, initially radioactive nuclei power electromagnetic transients called “kilonovae” that are observable in a merger's aftermath. In article 2200306, Stephan Rosswog and Oleg Korobkin discuss today's state-of-the-art of this active research field.

The observation rate of pulsar glitches is limited by their electromagnetic observations. There could be a population of the isolated neutron stars in the galaxy for which there is no electromagnetic observations, but they can produce gravitational waves. The all-sky search for gravitational waves provides better localization of the source sky position to mitigate the follow-up search with electromagnetic telescopes.

Population properties of double compact object mergers (especially binary black holes) are sensitive to the metallicity dependent cosmic star formation history. The uncertainty of this quantity cannot be ignored and makes the interpretation of current gravitational wave observations difficult. The origin of this sensitivity of gravitational wave sources to metallicity and the related challenges are discussed in this review.

The review gives an overview of the most recent advances in gravitational-wave (GWs) cosmology. After an in-depth discussion of methodologies and tools for GW cosmology, it presents the latest results on measurements of standard cosmological parameters from the LIGO, Virgo, and KAGRA detections.

During the third observing run (O3) of LIGO/Virgo interferometers new compact binary mergers have been observed, including some exceptional event like the first neutron star-black hole mergers. Events have been collected in three catalogs. The paper reviews the detections and the multi-messenger observations, together with the impact on astrophysics and cosmology.

Astro-(physics) has made major leaps forward through the combined information provided by both gravitational waves and electromagnetic emission from the first detected neutron star merger event. This review provides an up-to-date overview of today's understanding of neutron star mergers and their electromagnetic emission and it discusses possible research directions for the future.

This article presents the emission of gravitational radiation from an oscillating rod in Brans–Dicke theory. The content provides insight into gravitational waves without prior acquaintance with astrophysics, and a broad audience with an understanding of basic mechanics can comprehend it.

It is found that the upper limit of the scalar mode of GW170817 in term of the band-limited root-sum-square of the amplitude is $$4.37 \times 10^{-21}\text{ }[\mathrm{Hz^{-1/2}}]$$ with a time window of 2 [s] and frequency window of ≈60–120 [Hz]. Additionally, the simulation indicates that the reconstructed scalar mode in the direction to GW170817 contains roughly 30% of energy leaked from the tensor modes.

Transient noise appearing in the data from gravitational-wave detectors frequently causes problems such as instability of the detectors and overlapping or mimicking gravitational-wave signals. An architecture for classifying transient noise, which uses unsupervised deep learning combined with variational autoencoder and invariant information clustering, is proposed. In this study, the training process of the architecture is examined and reported.

This analysis is dedicated to the study of the prompt and afterglow emission of Swift Gamma-Ray Bursts (GRBs). A new machine learning technique is applied grouping the GRBs based on their morphological features. The afterglow is then studied using the “boosted fireball” model. The main result consists on best-fit parameter distributions that could describe the jet's physics of the sample.

A method of validating the performance of nested sampling, using likelihood insertion order statistics, is applied to the 45 events in the first two gravitational wave transient catalogs of the LIGO–Virgo collaboration. With few exceptions, the event-level order statistics are consistent with unbiased prior sampling. There is, however, weak evidence against uniformity at the catalog level.

Time-delay interferometry (TDI) is a crucial technique to remove the otherwise overwhelming laser frequency noise in space-borne gravitational-wave detectors. While standard TDI relies on a model of the measurement and the knowledge of inter-spacecraft light travel time delays, here they present a new model-independent and entirely data-driven algorithm to cancel laser noise for satellite constellations with time-varying arm lengths.