We present a systematic reassessment of cosmological constraints beyond ΛCDM by progressively relaxing the assumptions underlying Dark Energy (DE), Curvature, Neutrinos, and Inflation. Using the latest CMB data together with DESI BAO and different SN catalogues, we show that the preference for dynamical DE persists across all the extended cosmologies considered. Ωk remains compatible with flatness, despite a mild 2.2σ preference for Ωk > 0 that is substantially degraded in dynamical DE extensions. Constraints on Neff are broadly consistent with Neff=3.04, while cosmological upper limits on the total neutrino mass vary substantially across the cosmologies explored, ranging from ∑mν ≲ 0.06 eV to ≲ 0.2 eV. We quantify both the preference for the mass ordering and the apparent tension between cosmology and oscillation experiments, showing that they are strongly framework dependent. We find no evidence for inflationary tensor modes, with r ≲ 0.035. Constraints on the spectral index ns show significant model dependence. Allowing for the scalar runnings produces a mild shift toward αs > 0 and βs > 0 that can reabsorb the preference for larger ns found in small-scale CMB data, although both αs and βs remain consistent with zero at ∼ 1.5σ. We highlight the implications for slow-roll inflation and benchmark models. None of the extensions considered here can resolve the H0 tension. We discuss the implications for Ωm and S8. Overall, dynamical DE is the only significant deviation from ΛCDM and has the strongest impact on the inferred conclusions in the other sectors of the model.
This review explores the physical mechanisms driving the evolution of low- and intermediate-mass binary star systems, with particular emphasis on emerging mechanisms that challenge classical paradigms. We begin by describing the principal formation channels and orbital properties of binary systems. A critical reassessment of the Roche lobe formalism is presented, focusing on systems with eccentric orbits and asynchronous rotation, where deviations from traditional approximations become significant. We then review current theoretical models of mass and angular momentum exchange via Roche-lobe overflow, incorporating results from recent hydrodynamical simulations of wind accretion. The review also reports advances in tidal dissipation theory. Finally, we explore mechanisms capable of sustaining or exciting orbital eccentricity, including perturbations induced by mass transfer and interactions with circumbinary disks. These discussions aim to outline underexplored facets of binary evolution, offering new perspectives for theoretical and observational studies.
In this paper I review recent results on high-energy neutrino astronomy and what they can reveal about some of the most extreme cosmic accelerators. I discuss recent measurements of the diffuse TeV-PeV cosmic neutrino spectrum by the IceCube observatory and the current flux limits in the ultra-high-energy regime, contextualizing the recent detection of an ultra-high-energy neutrino by the KM3NeT observatory. I review the recent emergence of a TeV signal from nearby Seyfert galaxies such as NGC 1068, the potential of γ-ray blazars as neutrino sources above the PeV regime, and the current status of tidal disruption events and other transient classes as possible neutrino sources. For each of these topics, I discuss ongoing developments in source models and their current limitations. I argue for the indispensable role of next-generation multi-messenger facilities, such as IceCube-Gen2, in solidifying current source associations, probing the ultra-high-energy regime, and resolving vast transient populations that remain unidentified with current statistics.
Precise astrometric and photometric measurements of celestial point sources are fundamental to modern astronomy. These measurements, used to determine object positions, motions, and fluxes, are based on observational models that have evolved from empirical centroiding rules to rigorous probabilistic formulations at the pixel level. This review summarizes key contributions that formalized this transition and analyzes seminal works addressing both the theoretical limits and the empirical performance of estimators. Central to these developments is the derivation of fundamental bounds, such as the Cramér-Rao Lower Bound (CRLB), and the assessment of widely used estimators, including Maximum Likelihood (ML), Least Squares (LS), and Weighted Least Squares (WLS). These studies show that, while the CRLB sets a theoretical benchmark, practical estimators achieve it only under specific signal-to-noise ratio (SNR) regimes, with notable discrepancies in high-SNR conditions. Moreover, recent results demonstrate that jointly estimating source flux and background significantly improves photometric precision compared to sequential approaches. Looking ahead, the increasing complexity of astronomical surveys, driven by massive data volumes, dynamic observational conditions, and the integration of machine learning, poses new challenges to reliable inference. In this context, tools from statistical theory, including performance bounds and theoretically grounded estimators, remain critical to guide algorithm design and ensure robust astrometric and photometric pipelines.
The search for extrasolar photosynthetic life is one of the most important goals for modern astrobiology. Recent discoveries of cold brown dwarfs, as well as planets orbiting M-, G-, K-, and F-type main-sequence stars, have expanded opportunities to search for photosynthetic biosignatures within their habitable zones. This comprehensive review synthesizes current knowledge and emerging trends in the field. The paper addresses stellar variability and how spectral energy distribution influences potential pigment evolution and photoprotective adaptations, whether photosynthetic life could exist on peculiar exoworlds with specific illumination and surface conditions, as well as observational strategies with current and future telescopes. The goal of this work is to help researchers navigate the vast sea of knowledge by providing a strategic roadmap for prioritizing targets and interpreting potential biosignatures.
We review current challenges in understanding the values and origins of the spins of black holes in binaries. Thanks to recent advances in astrophysical instrumentation, the spins can now be measured using both gravitational waves emitted by merging black holes and electromagnetic radiation from accreting X-ray binaries containing black holes. A key finding of the gravitational-wave observatories is that premerger black holes in binaries have low spin values, with an average dimensionless spin parameter of a* ∼ 0.1–0.2, with 90% having a* ≲ 0.6. This implies that the natal spins of black holes are generally low, and the angular momentum transport in massive stars is efficient. On the other hand, most of the published spins in X-ray binaries are very high, a* ≳ 0.7. In particular, this is the case for binaries with high-mass donors (potential progenitors of mergers), where their published spins range from 0.8 to 1.0. At the same time, their short lifetimes prevent significant spin-up by accretion. Those with low-mass donors could be spun-up to a* ≳ 0.5 by conservative accretion. Spins a* ≳ 0.7 can be achieved only if the donor initial masses were more than several solar masses, which remains unproven. However, the existing methods of spin measurements suffer from significant systematic errors. The method relying on relativistic X-ray line broadening is based on the separation of the observed spectra into incident and reflected ones, which is intrinsically highly uncertain. The method relying on spectral fitting of accretion disk continua uses models that predict the disk to be highly unstable, while stability is observed. Improved stable models yield disk temperatures higher than the standard models, and consequently predict lower spins. The published spin measurements in X-ray binaries are uncertain. The spins of the binaries with high-mass donors may be low, while those with low-mass donors have a broader spin distribution, ranging from low to high, including high spins as required to power relativistic jets.
We review the results of the spectrophotometric and multi-band photometric observations of main-belt asteroids aimed at searching for signs of sublimation-driven dust activity (SDA) and the analysis of these signs with numerical simulations of light scattering. The reflectance spectra of 17 main-belt asteroids out of 112 objects, which were observed near perihelion after 2012, exhibited the signs of activity as a temporary dust exosphere. Among these 17 asteroids, there are 12 primitive asteroids of C, F, B, P, and D spectral types with low-temperature mineralogy and a low geometric albedo (<0.10) and 5 asteroids predominantly of X-type with mixed mineralogy and a relatively high geometric albedo (>0.10). In our view, the most important result of these observations is that SDA was almost simultaneously detected in several asteroids for each of the observation periods, which apparently suggests that this phenomenon is frequent and widespread in the Solar System. We also discuss why in ground-based observations the spectral method is more sensitive than the direct imaging method in detecting the signs of a thin dust exosphere on main-belt asteroids. The registered reflectance spectra of asteroids were analyzed in comparison with numerically modeled spectra of an active asteroid enveloped by a dust exosphere containing particles of various composition and morphology. This comparison made it possible to obtain an insight into the properties of a formed temporary dust exosphere. Particularly, it has been found that the dust exosphere of an active asteroid may contain aggregate particles of different composition and structure rather than just homogenous submicron ice and dust particles. A relatively stable though temporary SDA in a primitive-type asteroid is apparently indicative of water-ice deposits located near the surface of the body. As our investigations suggest, on main-belt primitive asteroids, the mechanism of SDA often operates in conjunction with meteoroid impacts and the electrostatic field formed near the sunlit surface of the bodies. At the same time, flares and eruptive events on the Sun may considerably influence the shape and extension of the dust exosphere.
When compact objects – neutron stars and black holes – are formed in a supernova explosion, they may receive a high velocity at formation, which may reach or even exceed 1000 km s−1 for neutron stars and hundreds of km s−1 for black holes. The origin of the velocity kick is intimately related to supernova physics. A better understanding of kick properties from astronomical observations will shed light on the unsolved problems of these explosions, such as the exact conditions leading to exotic electron capture and ultra-stripped supernovae.Kick velocities are profoundly important in several areas of astrophysics. Being a result of supernova explosions, the kick velocity distribution must be explained in the framework of the supernova mechanism. The kick magnitudes and directions influence many topics related to binary systems, including the rate of compact object coalescences observable through gravitational waves. Moreover, knowledge of the kick velocity distribution is significant in predicting future observational results and their interpretation. For example, it is expected that the Roman space telescope will discover many microlensing events related to neutron stars and black holes; accurate estimates of the number of observable microlensing events require precise kinematic properties of these compact objects.
The last decade has witnessed significant progress in our understanding of the growth of super-massive black holes (SMBHs). It is now clear that an Active Galactic Nucleus (AGN: the observed manifestation of a growing SMBH) is an "event" within the broader lifecycle of a galaxy, which can significantly influence the shape and evolution of the galaxy itself. Our view of the obscuring medium that affects the observed properties of an AGN has also undergone a revolution, and we now have a more physical understanding of the connection between the fuelling of (and feedback from) the SMBH and the broader host-galaxy and larger-scale environment. We have a greater understanding of the physics of SMBH accretion, can identify AGNs out to z = 8-10 witnessing the very earliest phases of SMBH growth, and have a more complete census of AGN activity than ever before. This great progress has been enabled by new innovative facilities, an ever-increasing quantity of multi-wavelength data, the exploitation and development of new techniques, and greater community-wide engagement. In this article we review our understanding of AGNs and the growth of SMBHs, providing an update of the earlier Alexander and Hickox (2012) review. Using citation-network analyses we also show where this review fits within the broader black-hole research literature and, adopting the previous article as a snapshot of the field over a decade ago, identify the drivers that have enabled the greatest scientific progress.
Airborne dust and water ice clouds are the two major atmospheric constituents on Mars that have the most dynamic impact on its atmosphere. Airborne dust strongly alters atmospheric temperatures, therefore significantly impacting Martian weather and climate. Martian water ice clouds also have radiative impacts (both direct and via dust cycle feedbacks) and provide insight into the Martian water cycle and important questions about habitability and life. Satellite observations spanning more than two decades play a pivotal role in understanding the meteorological processes associated with airborne dust and water ice clouds on Mars. Therefore, this study reviews dust devils, dust storms, and water ice clouds with the help of imaging observations made by the sensors onboard different Mars orbiters. We discuss their characteristics, correlations, and inter-annual variation in general, in order to help support modeling and forecasting. The vertical distribution of dust and water ice and their dynamical, microphysical, and radiative interactions need more attention as well. The aim is to predict the thermal behavior of the atmosphere accurately, considering the complex interplay of dust and water ice forcing with temperature.
The Gaia mission has triggered major developments in the field of Galactic dynamics in recent years, which we discuss in this review. The structure and kinematics of all Galactic components - disc, bar/bulge and halo - are now mapped in great detail not only in the Solar neighbourhood, but across a large part of the Milky Way. The dramatic improvements in the coverage and precision of observations revealed various disequilibrium processes, such as perturbations in the Galactic disc and the deformations of the outer halo, which are partly attributed to the interaction with satellite galaxies. The knowledge of the gravitational potential at all scales has also advanced considerably, but we are still far from having a consistent view on the key properties of the Galaxy, such as the bar pattern speed or the mass profile and shape of the dark halo. The complexity and interplay of several dynamical processes makes the interpretation of observational data challenging, and it is fair to say that more theoretical effort is needed to fully reap the fruit of the Gaia revolution.
Big Bang Nucleosynthesis (BBN), the process of creation of lightest elements in the early universe, is a highly robust, precise, and ultimately successful theory that forms one of the three pillars of the standard hot-Big-Bang cosmological model. Existing theoretical treatments of BBN and the associated computer codes are accurate and flexible, but are typically highly technical and opaque, and not suitable for pedagogical understanding of the BBN. Here we present BBN-simple – a from-scratch numerical calculation of the lightest element abundances pitched at an advanced undergraduate or beginning graduate level. We review the physics of the early universe relevant for BBN, provide information about the reaction rates, and discuss computational-mathematics background that is essential in setting up a BBN calculation. We calculate the abundances of the principal nuclear species in a standard cosmological model, and find a reasonably good agreement with public precision-level BBN codes. A condensed version of this paper and associated snippets of computer code are given at http://www-personal.umich.edu/~aidanmw/.
Understanding the status of water on Mars is crucial for evaluating its capacity to support life and to serve as a resource for future possible human exploration. Investigations have been carried out in the past to find signs of water in its past or present states. It is generally agreed that Mars had significant amounts of water early in its existence, but today, only remnants exist, mostly as ice or within hydrous minerals. Current evidence of water on Mars includes geological features, Martian meteorites, sporadic wet flows on slopes, surface moisture detected by missions like Curiosity and Phoenix, and features suggesting ancient lakes and rivers. A notable recent discovery was an old streambed in Gale Crater, indicating the presence of considerable water flow in the past, which might have supported microbial life. Nowadays, Mars' arid surface is not suitable for life as we know it, leading scientists to focus on underground environments for the exploration of life and its respective biosignatures. Recent efforts have unveiled substantial underground ice reserves discovered by NASA in 2016 and a hidden subglacial lake identified by Italian researchers in 2018. The question of life on Mars still remains unresolved to date. This overview compiles the findings from diverse studies on Mars' water history and attempts to address the ongoing discussions about the potential for life on the planet.
Several correlations among Gamma-Ray Bursts (GRBs) quantities, both in the prompt and afterglow emissions, have been established during the last decades, thus enabling the standardization of GRBs as cosmological probes. Since GRBs are observed up to redshift z ∼ 9, they represent a valuable tool to fill in the gap of information on the Universe evolution between the farthest type Ia supernovae and the Cosmic Microwave Background Radiation and to shed new light on the current challenging cosmological tensions. Without claiming for completeness, here we describe the state of the art of GRB correlations, their theoretical interpretations, and their cosmological applications both as standalone probes and in combination with other probes. In this framework, we pinpoint the importance of correcting the correlations for selection biases and redshift evolution to derive intrinsic relations, the assets of combining probes at different scales, and the need for the employment of the appropriate cosmological likelihood to precisely constrain cosmological parameters. Furthermore, we emphasize the benefits of the cosmographic approach to avoid any cosmological assumptions and the valuable applications of machine learning techniques to reconstruct GRB light curves and predict unknown GRB redshifts. Finally, we stress the relevance of all these factors, along with future observations, to definitely boost the power of GRBs in cosmology.
The hierarchical model of galaxy formation predicts that the Milky Way halo is populated by tidal debris of dwarf galaxies and globular clusters. Due to long dynamical times, debris from the lowest mass objects remains coherent as thin and dynamically cold stellar streams for billions of years. The Gaia mission, providing astrometry and spectrophotometry for billions of stars, has brought three fundamental changes to our view of stellar streams in the Milky Way. First, more than a hundred stellar streams have been discovered and characterized using Gaia data. This is an order of magnitude increase in the number of known streams, thanks to Gaia's capacity for identifying comoving groups of stars among the field Milky Way population. Second, Gaia data have revealed that density variations both along and across stellar streams are common. Dark-matter subhalos, as well as baryonic structures were theoretically predicted to form such features, but observational evidence for density variations was uncertain before Gaia. Third, stream kinematics are now widely available and have constrained the streams' orbits and origins. Gaia has not only provided proper motions directly, but also enabled efficient spectroscopic follow-up of the proper-motion selected targets. These discoveries have established stellar streams as a dense web of sensitive gravitational tracers in the Milky Way halo. We expect the coming decade to bring a full mapping of the Galactic population of stellar streams, as well as develop numerical models that accurately capture their evolution within the Milky Way for a variety of cosmological models. Perhaps most excitingly, the comparison between the two will be able to reveal the presence of dark-matter subhalos below the threshold for galaxy formation (~10^6 Msun), and provide the most stringent test of the cold dark matter paradigm on small scales.
Brown Dwarfs (BDs) are crucial objects in our understanding of both star and planet formation. However, there is still an unconcluded debate about which is the dominant formation mechanism of these objects. For this, it is mandatory to study BDs in their earliest evolutionary stages (what we call pre- and proto-BDs), comparable to the `pre-stellar' and `Class 0/I' stages well characterized for the formation of low-mass stars. In this review, the recent efforts aimed at searching, identifying and characterising pre- and proto-BD candidates in nearby star-forming regions are presented, and revised requirements for an object to be a promising proto-BD or pre-BD candidate are provided, based on a new, unexplored so far, relation between the internal luminosity and the accreted mass. By applying these requirements, a list of 67 promising proto-BD candidates is presented, along with a compilation of possible pre-BDs from the literature. Updated correlations of protostellar properties such as mass infall rate or outflow momentum rate with bolometric luminosity are provided down to the low-mass BD regime, where no significant deviations are apparent. Furthermore, the number of proto-BD candidates in different clouds of the Solar Neighborhood seem to follow the known relations of number of protostars with cloud properties. In addition, proto(star-to-BD) ratios for the different clouds are also explored, unveiling a particular underproduction of low-mass proto-BD candidates in Ophiuchus compared to Lupus and Taurus. Possible explanations for this behavior are discussed, including heating of the Ophiuchus cloud by the nearby OB stars. The overall results of this work tend to favor a star-like process for BD formation down to the planetary boundary, of about 10 Mjup, below which other mechanisms might be at work.
Although the Ku-band Cassini RADAR was not primarily designed to probe Titan’s subsurface structure, it unexpectedly provided valuable data on penetration, notably measuring the depth and dielectric properties of several lakes or seas in altimetry mode. While the RADAR did not possess the same penetration capability as the radar instruments that are used to search for water on Mars, its detection results and potential still warrant comprehensive integration and summary. This paper reviews the latest research findings on Titan’s subsurface observations, encompassing liquid bodies and dunes, grounded on RADAR’s penetration performance and principles. In consideration of the Dragonfly mission and its scientific goals, the paper reviews the distribution of water ice on Titan. The upcoming observations hold promise for investigating relevant features at low latitudes, such as impact craters with exposed ice-rich material. Finally, suggestions and prospects for future subsurface radar exploration of Titan are presented. The exploration of subsurface structures on Titan remains a captivating field of study, bearing significant implications for planetary science and astrobiology.
Wormholes have captured the interest of scientists and readers of science fiction as a fascinating possibility for traveling through huge cosmic distances or presumably enabling time travel. This review aims to present a thorough overview of wormholes in the context of modified gravity, highlighting the theoretical foundations, and significant developments in this rapidly developing area. In this article, we first give an overview of the concept of a wormhole in the different frameworks of modified gravities. Then this is followed by the wormhole framework, embedding diagrams, the existence of the wormholes, and thorough analysis in various modified gravities like f ( R ), f ( G ), f ( T ), f ( R , L m ), f ( R , T ), f ( Q ), and f ( Q , T ). For distinct purposes, various models have been created. Many authors have used a variety of techniques to get a solution. Hereafter, the emphasis will be on the stability analysis of wormholes through different approaches namely Energy Conditions (ECs), Tolman-Oppenheimer-Volkoff (TOV), Volume Integral Quantifier(VIQ), Active Gravitational Mass(AGM), and Total Gravitational Energy (TGE). The possible observable features of such wormholes are briefly discussed. All the solutions are organized by the suggested framework to demonstrate broad concepts of wormhole solutions.
In this review we show that the space experiment with gamma-ray detector with sensitivity 2 orders of magnitude higher than existing ones will make it possible to discover up to a thousand neutron star mergers, even at those moments when gravitational wave (GW) antennas are not working. At the same time, synchronous detection of neutron stars mergers by gamma-ray and GW detectors will make it possible not only to study in detail the physical processes occurring at the time of the catastrophe, but also to determine the full gamma ray beam pattern, including the average jet divergence angle and the real energy of the explosion. A gamma detector that has the required sensitivity at a relatively low flight weight is proposed. The latter, in turn, will make it possible to clarify our ideas about the genesis of double relativistic stars in the Universe.
The Gaia mission has revolutionized our view of the Milky Way and its satellite citizens. The field of Galactic Archaeology has been piecing together the formation and evolution of the Galaxy for decades, and we have made great strides, with often limited data, towards discovering and characterizing the subcomponents of the Galaxy and its building blocks. Now, the exquisite 6D phase-space plus chemical information from Gaia and its complementary spectroscopic surveys has handed us a plethora of data to pore over as we move towards a quantitative rather than qualitative view of the Galaxy and its progenitors. We review the state of the field in the post-Gaia era, and examine the key lessons that will dictate the future direction of Galactic halo research.
