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Cosmic rays at petaelectronvolt energies permeate the Milky Way, but their origin is unknown. This Review Article summarizes the physics required to accelerate particles to these ultrahigh energies, and their potential astrophysical sources (‘PeVatrons’).
This article reviews the developments on the topic of so-called changing-look active galactic nuclei from the past ten years or so. These active galactic nuclei show dramatic flux and spectral changes at X-ray, ultraviolet and optical wavelengths, due to either obscuration or changes in accretion rate.
Continuous gravitational waves represent an exciting new frontier for multi-messenger astrophysics. This overview discusses their origins and the results obtained in the LIGO–Virgo–KAGRA O3 observing run, highlighting their potential for future studies.
Upcoming X-ray microcalorimeter missions should deliver high spectral finesse, and allow detailed studies of accretion processes and feedback mechanisms in growing black holes.
Mars hosted hundreds of lakes, most of which formed earlier than 3.7 billion years ago and lasted only a limited amount of time. This overview of their characteristics and mineralogy highlights the importance of the Martian lakes as a record of ancient climate and potential for biogenesis.
Light pollution is a growing problem affecting the night sky. This Review takes a comprehensive look at the factors contributing to elevated brightness at night, the measurement techniques and the ongoing assessment of sky quality.
A number of recent laboratory studies—summarized in this Review—have improved our understanding of the origin of presolar grains, with at least a quarter of presolar grains now being understood to originate in supernovae and their progenitors.
This review summarizes our understanding of early-type dwarfs, which are the end-points of the evolution of low-mass galaxies. Their primeval stellar populations provide a unique laboratory for studying the physical conditions on small scales at epochs beyond z = 2.
Galaxies and their dark-matter haloes have posed several challenges to the dark energy plus cold dark matter (ΛCDM) cosmological model. This Review discusses the most notable challenges to ΛCDM regarding dwarf galaxies and the insights provided by recent cosmological numerical simulations.
This article reviews the properties of the dwarf galaxies of the Local Group from the point of view of their stellar dynamics and dark matter content and distribution, as inferred from the combination of observed data and dynamical models.
This Review looks at how the most recent results on intracluster light—the faint glow between galaxies within a galaxy cluster—fit into the current understanding of the field and provides a global perspective on the direction of future studies.
Our understanding of the relatively newly recognized phenomenon of haloes of gamma-ray emission around Galactic pulsars is summarized, from observational and theoretical perspectives, together with their implication for the acceleration of cosmic rays.
This Review examines gas dynamics in dwarf galaxies, such as rotation curves and mass models. Star-forming dwarfs extend the dynamical laws of spiral galaxies and show small scatter around them, implying a tight coupling between baryons and dark matter.
This Review summarizes what is known of the stellar and chemical properties of nearby (<20 Mpc) star-forming dwarf galaxies. These objects resemble the earliest formed galaxies and may thus represent a window on the distant, early Universe.
Theoretical findings and current gravitational-wave evidence of hierarchical stellar-mass black-hole mergers are reviewed. Promising locations for the production of such systems include nuclear star clusters, accretion disks in active galactic nuclei, and potentially globular clusters.
This Review Article summarizes our current understanding of ionized outflows in active galactic nuclei, observed in absorption in the ultraviolet and X-ray wavelengths, including the most relevant observations as well as their origin and acceleration mechanisms.
In the Spitzer Space Telescope’s 16 years of operation, it observed many Solar System objects and environments. In this first Review Article of a pair, Spitzer’s insights into comets, centaurs and Kuiper belt objects—all remnants of the Solar System’s formation—are summarized.
In the Spitzer Space Telescope’s 16 years of operation, it observed many Solar System objects and environments. In this second Review Article of a pair, Spitzer’s insight into asteroids, dust clouds and rings and the ice giant planets are summarized.
The Spitzer Space Telescope launched when the study of exoplanets was in its infancy, and yet it was remarkably successful in characterizing both exoplanet and brown dwarf systems through their mid-infrared emissions. This Review collates the highlights of Spitzer-based research in these fields.
Spitzer revealed the properties of luminous and ultraluminous infrared galaxies, the role of starbursts and actively accreting supermassive black holes in powering these sources and found evidence for energetic feedback on their interstellar gas and dust.
