Discovery Of Gravitational Waves Research Articles

Primordial black holes as a dark matter candidate - a brief overview

Historically the most popular dark matter candidates have been new elementary particles, such as Weakly Interacting Massive Particles and axions. However Primordial Black Holes (PBHs), black holes formed from overdensities in the early Universe, are another possibility. The discovery of gravitational waves from mergers of tens of Solar mass black hole binaries by LIGO-Virgo has generated a surge in interest in PBH dark matter. We overview the formation of PBHs, observational probes of their abundance, and some of the key open questions in the field.

Probing astrophysical environment with eccentric extreme mass-ratio inspirals

The discovery of gravitational waves and black holes has started a new era of gravitational wave astronomy that allows us to probe the underpinning features of gravity and astrophysics in extreme environments of the universe. In this article, we investigate one such study with an extreme mass-ratio inspiral system where the primary object is a spherically symmetric static black hole immersed in a dark matter halo governed by the Hernquist density distribution. We consider the eccentric equatorial orbital motion of the steller-mass object orbiting around the primary and compute measurable effects. We examine the behaviour of dark matter mass and halo radius in generated gravitational wave fluxes and the evolution of eccentric orbital parameters- eccentricity and semi-latus rectum. We further provide an estimate of gravitational wave dephasing and find the seminal role of low-frequency detectors in the observational prospects of such an astrophysical environment.

Prophetic detection and discovery of gravitational waves

Einstein's general relativity theory includes the gravitational wave as a key prediction. One of the most crucial areas of contemporary physics is gravitational wave detection. A fantastic addition to conventional electromagnetic radiation astronomy, gravitational wave astronomy is a brand-new field of study based on the discovery of gravitational waves. In this paper, the prediction and characteristics of gravitational waves are discussed, and the detection methods of gravitational waves are given, such as the limitations of the resonant rod of gravitational waves, the working principle and basic structure of the gravitational wave probe, the laser interferometer. The gravitational wave signal of the binary black hole merger detected by the LIGO laser interferometer gravitational wave detector in the United States for the first time on September 14, 2015, which opens a new "gravitational wave window" for human astronomy research. It is foreseeable that in the near future gravitational wave research will explore the unknown information of the universe from various gravitational wave frequency bands.

Research on the classifications of gravitational wave

In daily life, we can transmit and obtain information through mechanical waves and electromagnetic waves. For example, judging where the fish swims from the flooded water waves, and learns from the wonderful music to know what kind of instrument the musicians are playing and communicating through the radio waves. Gravitational waves, a fundamental prediction of Einstein's theory of general relativity, have revolutionized our understanding of the universe. This essay explores the background of research on gravitational waves, tracing their theoretical origins to the early 20th century and highlighting their recent detection in 2015. The research technique employed involves highly sensitive interferometers, such as LIGO and Virgo, which can detect the minuscule distortions in space-time caused by these elusive waves. By observing the gravitational waves emitted during cataclysmic cosmic events, scientists can now delve deeper into the nature of black holes, neutron stars, and the origin of our universe. In conclusion, the discovery of gravitational waves opens up new avenues for exploring the cosmos, providing unprecedented insights into the fabric of space-time itself.

Virtual reality in astronomy education: reflecting on design principles through a dialogue between researchers and practitioners

ABSTRACT Virtual reality (VR) technologies have the potential to transform astronomy education practices profoundly: new forms of visual representations, perceptual engagement and embodied participation promise authentic learning experiences in formal and informal learning spaces. While a growing body of research studies the educational needs and opportunities of VR astronomy education from the learner’s perspective, relatively few studies have explored the perspectives of education and public outreach (EPO) professionals. This study aims to turn our attention to these complementary perspectives and shed light on design considerations for using VR in astronomy education. We unpack design principles as a dialogue between researchers and practitioners, framing this dialogue as an act of reflective practice. The findings and the ensuing dialogue draw on data from two focus group interviews with EPO professionals and scientists from the Australian Research Council Centre of Excellence for Gravitational Wave Discovery. Our design principles centre on aspects of immersion, visualisation, facilitation, and collaboration and can guide astronomy educators who wish to use VR in formal and informal learning environments. Besides, our study contributes to a deeper understanding of the new learning contexts VR technologies can create in astronomy education.

CLOSED BKS-TYPE UNIVERSES AND DIRAC SPIN EFFECT IN THE RAINBOW GRAVITY

The result related to astrophysical datasets suggest that our universe has recently entered a phase of accelerated expansion. This accelerated expansion is not a situation predicted by the general theory of relativity. Therefore, the emergence of alternative approaches to general relativity has become inevitable. Modifying general relativity and absolute parallelism theory are just two of these theories. In addition, with the discovery of gravitational waves, the need for a view that includes gravitational quantum contributions arose. In this context, rainbow gravity has an approach that also offers quantum contributions to the theory of general relativity and absolute parallelism. In this study, axial vector torsion is calculated for BKS-type universe models using the rainbow gravity formalism. With the calculations made, the vector part and axial vector part components of the torsion tensor are obtained. The spin process, which contributes to the Dirac particles, is also investigated using the rainbow gravitational theory. However, since the obtained axial vector fragment is in time-like form, it is concluded that the spin vector of the Dirac particle is constant. The axial part of the torsion tensor for general BKS-type universe models is calculated and presented in a table for some well-known rainbow functions.

Probing minimal grand unification through gravitational waves, proton decay, and fermion masses

Motivated by the direct discovery of gravitational waves (GWs) from black holes and neutron stars, there is a growing interest in investigating GWs from other sources. Among them, GWs from cosmic strings are particularly fascinating since they naturally appear in a large class of grand unified theories (GUTs). Remarkably, a series of pulsar-timing arrays (PTAs) might have already observed GWs in the nHz regime, hinting towards forming a cosmic string network in the early universe, which could originate from phase transition associated with the seesaw scale emerging from GUT. In this work, we show that if these observations from PTAs are confirmed, GWs from cosmic strings, when combined with fermion masses, gauge coupling unification, and proton decay constraints, the parameter space of the minimal SO(10) GUT becomes exceedingly restrictive. The proposed minimal model is highly predictive and will be fully tested in a number of upcoming gravitational wave observatories.

Quiescent and Active Galactic Nuclei as Factories of Merging Compact Objects in the Era of Gravitational Wave Astronomy

Galactic nuclei harbouring a central supermassive black hole (SMBH), possibly surrounded by a dense nuclear cluster (NC), represent extreme environments that house a complex interplay of many physical processes that uniquely affect stellar formation, evolution, and dynamics. The discovery of gravitational waves (GWs) emitted by merging black holes (BHs) and neutron stars (NSs), funnelled a huge amount of work focused on understanding how compact object binaries (COBs) can pair up and merge together. Here, we review from a theoretical standpoint how different mechanisms concur with the formation, evolution, and merger of COBs around quiescent SMBHs and active galactic nuclei (AGNs), summarising the main predictions for current and future (GW) detections and outlining the possible features that can clearly mark a galactic nuclei origin.

Aspects of Quantum Gravity Phenomenology and Astrophysics

With the discovery of gravitational waves, the search for the quantum of gravity, the graviton, is imminent. We discuss the current status of the bounds on graviton mass from experiments as well as the theoretical understanding of these particles. We provide an overview of current experiments in astrophysics such as the search for Hawking radiation in gamma-ray observations and neutrino detectors, which will also shed light on the existence of primordial black holes. Finally, the semiclassical corrections to the image of the event horizon are discussed.

Gravitational wave constraints on spatial covariant gravities

The direct discovery of gravitational waves (GWs) from the coalescence of compact binary components by the LIGO/Virgo/KAGRA Collaboration provides an unprecedented opportunity for exploring the underlying theory of gravity that drives the coalescence process in the strong and highly dynamical field regime of gravity. In this paper, we consider the observational effects of spatial covariant gravities on the propagation of GWs in the cosmological background and obtain the observational constraints on coupling coefficients in the action of spatial covariant gravities from GW observations. We first decompose the GWs into the left- and right-hand circular polarization modes and derive the effects of the spatial covariant gravities on the propagation equation of GWs. We find that these effects can be divided into three classes: 1) frequency-independent effects on GW speed and friction, 2) parity-violating amplitude and velocity birefringences, and 3) a Lorentz-violating damping rate and dispersion of GWs. With these effects, we calculate the corresponding modified waveform of GWs generated by the coalescence of compact binaries. By comparing these new effects with the publicly available posterior samples or results from various tests of gravities with LIGO/Virgo/KAGRA data in the literature, we derive the observational constraints on coupling coefficients of the spatial covariant gravities. These results represent the most comprehensive constraints on the spatial covariant gravities in the literature.

Observational Imprints of Enhanced Scalar Power on Small Scales in Ultra Slow Roll Inflation and Associated Non-Gaussianities

The discovery of gravitational waves from merging binary black holes has generated considerable interest in examining whether these black holes could have a primordial origin. If a significant number of black holes have to be produced in the early universe, the primordial scalar power spectrum should have an enhanced amplitude on small scales, when compared to the COBE normalized values on the large scales that is strongly constrained by the anisotropies in the cosmic microwave background. In the inflationary scenario driven by a single, canonical scalar field, such power spectra can be achieved in models that permit a brief period of ultra slow roll inflation during which the first slow roll parameter decreases exponentially. In this review, we shall consider a handful of such inflationary models as well as a reconstructed scenario and examine the extent of formation of primordial black holes and the generation of secondary gravitational waves in these cases. We shall also discuss the strength and shape of the scalar bispectrum and the associated non-Gaussianity parameter that arise in such situations. We shall conclude with an outlook wherein we discuss the wider implications of the increased strengths of the non-Gaussianities on smaller scales.

Properties and Patterns of Polarized Gravitational Waves

We discuss the polarization of gravitational radiation within the standard framework of linearized general relativity. The recent experimental discovery of gravitational waves provides the impetus to revisit the implications of the spin-rotation-gravity coupling for polarized gravitational radiation; therefore, we consider the coupling of the helicity of gravitational waves to the rotation of an observer or the gravitomagnetic field of a rotating astronomical source. Observational possibilities regarding polarization-dependent effects in connection with future gravitational wave detectors are briefly explored.

Development of large-aperture radio telescopes and applications of coupled structural-electromagnetic theory

<p indent="0mm">The smooth operation of radio telescopes is essential in radio astronomy. This paper establishes the importance of radio telescopes via examples of the discovery of gravitational waves, the merger of neutron stars, and the first black hole photograph. As radio astronomy advances, radio telescopes require larger apertures and higher pointing accuracy, resulting in a closer structural-electromagnetic coupling. To solve the coupled structural-electromagnetic problem of radio telescopes, the development of a coupled structural-electromagnetic theory is key to the smooth and efficient operation of large-aperture radio telescopes. To this end, this paper describes the development of radio telescopes built and put into operation in the last decade, as well as those under construction and to be built, and emphasizes the importance of coupled structural-electromagnetic theory in the design, manufacture, and operation of radio telescopes. Then, the paper systematically summarizes the application of coupled structural-electromagnetic theory in radio telescopes. Finally, future research hotspots of electromechanical coupling are proposed based on the development of radio astronomy and the performance requirements of large-aperture radio telescope antennas.

How Have Astronomers Cited Other Fields in the Last Decade?

We present a citation pattern analysis between astronomical papers and 13 other disciplines, based on the arXiv database over the past decade (2010–2020). We analyze 12,600 astronomical papers citing over 14,531 unique publications outside astronomy. Two striking patterns are unraveled. First, general relativity recently became the most cited field by astronomers, a trend highly correlated with the discovery of gravitational waves. Second, the fast growth of referenced papers in computer science and statistics, the first with a notable 15 fold increase since 2015. Such findings confirm the critical role of interdisciplinary efforts involving astronomy, statistics, and computer science in recent astronomical research.

Implementation of a generalized precession parameter in the RIFT parameter estimation algorithm

Since the initial discovery of gravitational waves in 2015, significant developments have been made towards waveform interpretation and estimation of compact binary source parameters. We present herein an implementation of the generalized precession parameter ⟨χ p⟩ [Gerosa et al 2021], which averages over all angular variations on the precession timescale, within the RIFT parameter estimation framework. Relative to the precession parameter χ p, which characterizes the single largest dynamical spin in a binary, ⟨χ p⟩ has a unique domain 1 < ⟨χ p⟩ < 2, which is exclusive to binaries with two precessing spins. After reviewing the physical differences between these two parameters, we describe how ⟨χ p⟩ was implemented in RIFT and apply it to all 36 events from the second half of the Advanced LIGO and Advanced Virgo third observing run (O3b). In O3b, ten events show significant amounts of precession ⟨χ p⟩ > 0.5. Of particular interest is GW191109_010717; we show it has a probability that the originating system necessarily contains two misaligned spins.

Constraints on the Nieh-Yan modified teleparallel gravity with gravitational waves

The discovery of gravitational waves (GWs) from the compact binary components by LIGO/Virgo Collaboration provides an unprecedented opportunity for testing gravity in the strong and highly dynamical field regime of gravity. Currently a lot of model-independent tests have been performed by LIGO/Virgo Collaboration and no any significant derivation from general relativity has been found. In this paper, we study the parity violating effects on the propagation of GWs in the Nieh-Yan modified teleparallel gravity, a theory which modifies general relativity by a parity violating Nieh-Yan term. We calculate the corresponding parity violating waveform of GWs produced by the coalescence of compact binaries. By comparing the two circular polarization modes, we find the effects of the velocity birefringence of GWs in their propagation caused by the parity violation due to the Nieh-Yan term, which are explicitly presented in the GW waveforms by the phase modification. With such phase modifications to the waveform, we perform the full Bayesian inference with the help of the open source software Bilby on the GW events of binary black hole merges (BBH) in the LIGO-Virgo catalogs GWTC-1 and GWTC-2. We do not find any significant evidence of parity violation due to the parity violating Nieh-Yan term and thus place an upper bound on the energy scale ${M}_{\mathrm{PV}}&lt;6.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}42}\text{ }\text{ }\mathrm{GeV}$ at 90% confidence level, which represents the first constraint on the Nieh-Yan modified teleparallel gravity so far.

Dedicated SiPM array for GRD of GECAM

PurposeThe discovery of gravitational waves and gamma-ray bursts heralds the era of multi-messenger astronomy. With the adoption of two small satellites to achieve the all-sky monitoring of gamma-ray bursts, the gravitational wave high-energy electromagnetic counterpart all-sky monitor (GECAM) possesses a quasi-real-time early warning ability and plays an important role in positioning the sources of gravitational waves and in subsequent observations. Each satellite of GECAM was fitted with 25 3-inch-diameter gamma-ray detectors (GRD), covering an energy range of 8–2 MeV. GRDs have adopted silicon photomultiplier tubes (SiPM) in lieu of photomultiplier tubes (PMT) to adapt to the dimensional limitations of micro-satellites.MethodsA unique 3-inch circular SiPM array was designed. In this design, 64 6 × 6 mm chips were arranged evenly in a circular manner with the seams filled with reflecting films, thus achieving satisfactory uniformity of light collection. The integrated pre-amplifier circuit on the back of the SiPM array adopted two-level grouping and summing; further, it achieved a satisfactory signal-to-noise ratio. Two high-gain and low-gain channels were adopted to achieve a large dynamic range, and two independent power supply units were used, where each unit can be closed separately, thus improving reliability.ResultsPerformance studies show that this SiPM array meets the requirements of GECAM.ConclusionA 3-inch SiPM array have been developed that uses grouped summation, reflective films, a circular arrangement, two groups of independent power supplies, high- and low-gain signals, differential signal output technologies, etc. This solution can be used not only for GECAM, but also as a general solution for SiPM-based scintillation detectors.

Quantum Legacies: Dispatches from an Uncertain World

Quantum Legacies: Dispatches from an Uncertain World

Search for Radio Remnants of Nearby Off-axis Gamma-Ray Bursts in a Sample of Swift/BAT Events

Abstract The multi-messenger discovery of gravitational waves (GWs) and light from the binary neutron star (NS) merger GW170817, associated with gamma-ray burst (GRB) 170817A and kilonova AT2017gfo, has marked the start of a new era in astrophysics. GW170817 has confirmed that binary NS mergers are progenitors of at least some short GRBs. The peculiar properties of the GRB 170817A radio afterglow, characterized by a delayed onset related to the off-axis geometry, have also demonstrated how some nearby short GRBs may not be identified as such with standard short-timescale electromagnetic follow-up observations. Building upon this new information, we performed late-time radio observations of a sample of four short GRBs with unknown redshift and no previously detected afterglow in the Swift/BAT sample in order to identify nearby ( Mpc) off-axis GRB candidates via their potential late-time radio signatures. We find a previously uncatalogued radio source within the error region of GRB 130626 with a flux density consistent with an NS radio flare at a distance of ∼100 Mpc. An origin related to a persistent radio source unrelated to the GRB cannot be excluded nor confirmed given the high chance of false positives in error regions as large as those considered here, and the limited time baseline of our observations. Further radio (and X-ray) follow-up observations are needed to better understand the origin of this source.

Experience gravity in the classroom using the rubber sheet: an educational proposal from the collaboration between university and school

Teaching modern physics in high school is of increasingly importance as it can offer students a more realistic and updated vision of the world, and can provide an opportunity to understand the most recent scientific discoveries. In this context, general relativity (GR) occupies a prominent place, since it is related to astonishing scientific results, such as the first image of a black hole or the discovery of gravitational waves. In this paper we describe an educational proposal aimed at teaching GR in high schools in a fun and playful way using the so-called rubber sheet analogy. We present a set of instructions to build a simple and low-cost space-time simulator, and a series of related educational cards that guide the teacher in the implementation of the activities step by step. This work is the result of a long and productive debate among Italian high school teachers who have collaborated for many years with the Department of Mathematics and Physics of Roma Tre University in Rome. As our proposal relies on the collaboration with the final users, we believe that it will meet their needs and expectations, and it will help to treat GR in high school more and more over time.