Gravitational waves (GW) have revolutionised the field of astronomy by providing scientists with a new way to observe the Universe and gain a better understanding of exotic objects like black holes. Several large-scale laser interferometric GW detectors have been constructed worldwide, with a focus on achieving the best possible sensitivity. However, in order for a detector to operate at its intended

This study explores the properties of quark stars (QSs) formulated with an interacting quark matter equation of state within the framework of Rastall gravity, a modified theory of gravity. We derive the mass-radius relationships and calculate the maximum gravitational masses and their corresponding radii, comparing these results under both Rastall gravity and general relativity. Our analysis incorporates

Doubly special relativity (DSR) is usually regarded as a low-energy limit of a quantum gravity theory with testable predictions. On the other hand, non-local quantum field theories have been presented as a solution to the inconsistencies arising when quantizing gravity. Here, we present a new formulation of quantum field theories in DSR with non-local behavior. Our construction restricts the models

The radio emission from pulsars can scatter from inhomogeneities in the charged particle distribution in the interstellar medium (ISM) in a process called scintillation. The interference caused by this scattering creates bright peaks in a pulsar’s dynamic spectrum, yielding a characteristic ‘scintillation bandwidth’ that depends on density enhancements in the ISM along the line of sight to the pulsar

Four years ago the Japan Aerospace Exploration Agency's Hayabusa2 mission returned samples of an asteroid to Earth. The latest results in the analysis of the sample material are presented in this issue of Nature Astronomy.

Current- and next-generation gravitational-wave observatories may reveal new, ultralight bosons. Through the superradiance process, these theoretical particle candidates can form clouds around astrophysical black holes and result in detectable gravitational-wave radiation. In the absence of detections, constraints—contingent on astrophysical assumptions—have been derived using LIGO-Virgo-KAGRA data

Five new families of noncommutative lightcones in dimensions are presented as quantizations of the inequivalent Poisson homogeneous structures that emerge when the lightcone is constructed as a homogeneous space of the SO(2,1) conformal group. Each of these noncommutative lightcones maintains covariance under the action of the respective quantum deformation of the SO(2,1) conformal group. We discuss

We look for a classical double-copy-inspired relation between gravity and electrodynamics by connecting the descriptions of the scattering of two point masses, and of two point charges, in terms of perturbative (post-Minkowskian or post-Lorentzian) expansions. We do so by recasting available analytical information within the effective-one-body formalism using Kerr–Schild gauges in both cases. Working

As modern astronomy matures, individual researchers are becoming increasingly specialized, often at the expense of detailed knowledge in other fields; meanwhile, the dissemination of the vast datasets being collected by today’s telescopes is limited by the work hours available in the research community. The recent and rapid development of large language models (LLMs) may present a solution to both

Shown here is the circumstellar environment, as seen in the near-infrared (2.2 μm), of a massive star in another galaxy: WOH G64 in the Large Magellanic Cloud. The central ellipse is likely to be an opaque, dusty cocoon surrounding the extreme red supergiant. The faint elliptical structures around the central object might correspond to the inner rim of a circumstellar disk or torus. This image may

Iron-60 and aluminium-26 are unique chemical isotopes produced by stellar nucleosynthesis in our Galaxy and beyond. The ratio of these isotopes is a key parameter in understanding stellar evolution, but there is a known discrepancy between the value obtained from gamma-ray telescopes and that predicted by supernova models. Recently Artemis Spyrou and colleagues reported a cross-section of the neutron-capture

The carbon/oxygen (C/O) ratio in exoplanetary atmospheres is often used as a diagnostic tool for the formation history of giant planets. Chih-Chun Hsu and colleagues measure the C/O ratio of the protoplanet PDS 70 b, which is still embedded in the cavity of its protoplanetary disc and thus allows us, together with the other protoplanet PDS 70 c, to test our theories of in situ planetary formation directly

In an attempt to simulate black hole echoes (generated by potential quantum-gravitational structure) in numerical relativity, we recently described how to implement a reflecting boundary outside of the horizon of a black hole in spherical symmetry. Here, we generalize this approach to spacetimes with no symmetries and implement it numerically using the generalized harmonic formulation. We cast the

Bell-network states are a class of entangled states of the geometry that satisfy an area-law for the entanglement entropy in a limit of large spins and are automorphism-invariant, for arbitrary graphs. We present a comprehensive analysis of the effective geometry of Bell-network states on a dipole graph. Our main goal is to provide a detailed characterization of the quantum geometry of a class of

Next-generation gravitational-wave detectors, with their improved sensitivity and wider frequency bandwidth, will be capable of observing almost every compact binary coalescence signal from epochs before the first stars began to form, increasing the number of detectable binaries to hundreds of thousands annually. This will enable us to observe compact objects through cosmic time, probe extreme matter

The depleted mantle reservoir is that part of Earth's mantle from which crust has been extracted, leaving the remaining mantle depleted in incompatible elements. Knowing how and when it formed is essential for understanding the chemical evolution of Earth, including formation of continental crust. The best-constrained Hf isotope data presented here indicate that the mantle does not become significantly

Minna de Honkoku began as an online citizen science project to transcribe earthquake-related historical materials from the Earthquake Research Institute Library of the University of Tokyo. In Japan, almost all the documents are written in kuzushiji (old-style Japanese cursive script), a writing style used before ∼1900. Because the style of writing is different modern Japanese, transcription is necessary

The study of the polarisation of light is a powerful tool for probing the physical and compositional properties of astrophysical sources, including Solar System objects. In this article, we provide a comprehensive overview of the state-of-the-art in polarimetric studies of various celestial bodies within our Solar System: planets, moons, asteroids, and comets. Additionally, we review relevant laboratory

We consider the emergence of large-scale cosmological expansion in scalar–tensor theories of gravity. This is achieved by modelling sub-horizon regions of space-time as weak-field expansions around Minkowski space, and then subsequently joining many such regions together to create a statistically homogeneous and isotropic cosmology. We find that when the scalar field can be treated perturbatively,

We show that the consequences of a recent paper on quantum gravity are (1) a duality between point particles and massive scalar propagators, (2) the recovery of the entropy of a boundary (a black hole) in the same form as that of the EFT approach to quantum gravity and (3) a quantum correction to Hawking radiations and a Page-like curve. In this recent paper, information about what lies inside a boundary

We propose a solution to a classic problem in gravitational physics consisting of defining the spin associated with asymptotically-flat spacetimes. We advocate that the correct asymptotic symmetry algebra to approach this problem is the generalized–BMS algebra instead of the BMS algebra used hitherto in the literature for which a notion of spin is generically unavailable. We approach the problem of

We give a full classification of general affine connections on Galilei manifolds in terms of independently specifiable tensor fields. This generalises the well-known case of (torsional) Galilei connections, i.e. connections compatible with the metric structure of the Galilei manifold. Similarly to the well-known pseudo-Riemannian case, the additional freedom for connections that are not metric-compatible

A theory of gravity alternative to general relativity is trace-free Einstein gravity, which has the remarkable property that the cosmological constant emerges as an integration constant. In this paper, we report two fully diffeomorphism-invariant actions for trace-free Einstein gravity. They describe the theory as two BF theories supplemented with some constraints. The first action comprises two copies

In this study, we investigate the numerical stability of the covariant Baumgarte–Shapiro–Shibata–Nakamura (cBSSN) formulation against the Friedmann–Lemaitre–Robertson–Walker spacetime. To evaluate the numerical stability, we calculate the constraint amplification factor by the eigenvalue analysis of the evolution of the constraint. We propose a modification to the time evolution equations of the cBSSN

This work introduces the Elliptica pseudo-spectral code for generating initial data of binary neutron star systems. Building upon the recent Elliptica code update, we can now construct initial data using not only piecewise polytropic equations of state, but also tabulated equations of state for these binary systems. Furthermore, the code allows us to endow neutron stars within the binary system with

Nonassociative modifications of general relativity, GR, and quantum gravity, QG, models naturally arise as star product and R-flux deformations considered in string/M-theory. Such nonassociative and noncommutative geometric and quantum information theories were formulated on phase spaces defined as cotangent Lorentz bundles enabled with nonassociative symmetric and nonsymmetric metrics and nonlinear

This work explores the relation between two data-analysis methods used in the search for continuous gravitational waves in LIGO-Virgo-KAGRA data: the -statistic and the 5-vector method. We show that the 5-vector method can be derived from a maximum likelihood framework similar to the -statistic. Our analysis demonstrates that the two methods are statistically equivalent, providing the same detection

We revisit the static spherically symmetric solutions of Einstein’s general relativity with a conformally coupled scalar field in arbitrary dimensions. Using a four rank tensor introduced earlier we recast the field equations in a manifestly symmetric form to elucidate a somewhat less-known feature of dual mapping between solutions. We also show that there is a two-parameter subfamily of solutions

We study the semi-classical limit of the recently proposed coherent spin foam model for (2+1) Lorentzian quantum gravity. Specifically, we analyze the gluing equations derived from the stationary phase approximation of the vertex amplitude. Typically these exhibit two solutions yielding a cosine of the Regge action. However, by inspection of the algebraic equations as well as their geometrical realization

We revisit the theory of timelike and null geodesics in the (extended) Kerr spacetime. This work is a sequel to a recent paper by Cieślik, Hackmann, and Mach, who applied the so-called Biermann–Weierstrass formula to integrate Kerr geodesic equations expressed in Boyer–Lindquist coordinates. We show that a formulation based on the Biermann–Weierstrass theorem can also be applied in horizon-penetrating

Pulsar timing array (PTA) searches for gravitational waves (GWs) aim to detect a characteristic correlation pattern in the timing residuals of galactic millisecond pulsars. This pattern is described by the PTA overlap reduction function (ORF) , which is known as the Hellings–Downs (HD) curve in general relativity (GR). In theories of modified gravity, the HD curve often receives corrections. Assuming

We study the internal dynamics of a hypothetical spaceship traveling on a close timelike curve in an axially symmetric Universe. We choose the curve so that the generator of evolution in proper time is the angular momentum. Using Wigner’s theorem, we prove that the energy levels internal to the spaceship must undergo spontaneous discretization. The level separation turns out to be finely tuned so that

In the present study, we generalize the possible ghost field configurations within the framework of k-essence theory to the Simpson–Visser metric area function . Our analysis encompasses field configurations for the region-defined metric function as well as the general solution that asymptotically behaves as Schwarzschild-de Sitter for . Specifically, we investigate two scalar field configurations

Into the Unknown: The Quest to Understand the Mysteries of the Cosmos Kelsey JohnsonBasic Books: 2024. 416pp. $32.50 If your sense of wonder at the Universe and how on earth we got here needs a refresh, Johnson’s sweeping and highly accessible new tour of the outstanding ‘mysteries’ of cosmology is the book for you. Starting with some thoughtful — and somewhat humbling — real talk on matters such as

Stellar occultations provide a powerful tool to explore objects of the outer solar system. The Gaia mission now provides milli-arcsec accuracy on the predictions of these events and makes possible observations that were previously unthinkable. Occultations return kilometric accuracies on the three-dimensional shape of bodies irrespective of their geocentric distances, with the potential of detecting

Critical minerals are essential for sustaining the supply chain necessary for the transition to a carbon-free energy source for society. Copper, nickel, cobalt, lithium, and rare earth elements are particularly in demand for batteries and high-performance magnets used in low-carbon technologies. Copper, predominantly sourced from porphyry deposits, is critical for electricity generation, storage, and

We propose a new phenomenological second order gravity theory to be denoted as ‘Schouten–Codazzi’ Gravity’ (SCG), as it is based on Schouten and Codazzi tensors. The theory is related, but is clearly distinct from Cotton gravity. By assuming as source the energy momentum of General Relativity, we form a second order system with its geometric sector given by the sum of the Schouten tensor and a generic

Ecologists rely on a wealth of data, including field observations and light stable isotopes, to infer dietary preferences and other ecological and physiological properties in living mammals. But inferring such important traits (e.g., trophic position, metabolism, pathologies) in extinct animals, including humans, can be challenging because biological processes rarely mirror morphology as preserved

Massive higher spin fields are notoriously difficult to introduce interactions when they are described by symmetric (spin)-tensors. An alternative approach is to use chiral description that does not have unphysical longitudinal modes. For low spin fields we show that chiral and symmetric approaches can be related via a family of invertible change of variables (equivalent to parent actions), which should

The validity of the cosmic no-hair theorem for polytropic perfect fluids has been established by (Brauer et al 1994 Class. Quantum Grav. 11 2283) within the context of Newtonian cosmology, specifically under conditions of exponential expansion. This paper extends the investigation to assess the nonlinear stability of homogeneous Newtonian cosmological models under general accelerated expansion for

Over the past decades, there has been significant progress in our understanding of accreting supermassive black holes (SMBHs) that drive active galactic nuclei (AGNs), both from observational and theoretical perspectives. As an iconic target for this area of study, the nearby giant elliptical galaxy M 87 has received special attention thanks to its proximity, large mass of the central black hole and

Noise in various interferometer systems can sometimes couple non-linearly to create excess noise in the gravitational wave (GW) strain data. Third-order statistics, such as bicoherence and biphase, can identify these couplings and help discriminate those occurrences from astrophysical GW signals. However, the conventional analysis can yield large bicoherence values even when no phase-coupling is present

We embed the Penrose limit into the Weyl classical double copy. Thereby, we provide a lift of the double copy properties of plane wave spacetimes into black hole geometries and we open a novel avenue towards taking the classical double copy beyond statements about algebraically special backgrounds. In particular, the Penrose limit, viewed as the leading order Fermi coordinate expansion around a null