Reviews & Analysis

Computer simulations based on the prevailing cosmological model, ΛCDM, reproduce many observed properties of our Universe. But a study of coherent satellite motions in galaxy clusters yields discrepancies that challenge the definition of ‘today’.

Based on physical modelling and using deep-learning tools, a 3D reconstruction of a flare orbiting the black hole Sagittarius A*, at the centre of the Milky Way, provides observational clues to the formation of high-energy flares and the dynamics of black-hole accretion disks.

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’).

Although both are rocky planets in the habitable zone, Venus and Earth followed different climate evolutionary paths. This Perspective argues for the importance of Venus for understanding planetary habitability and terrestrial planet evolution.

What mechanisms power the heating of the solar atmosphere is a long-standing, complex question. Satellite and sounding-rocket observations, coupled with computer simulations, now support the idea that dissipation of electrical currents causes strong heating in the brightest parts of the solar chromosphere and corona.

Analysis of archival XMM-Newton data yields measurements of stellar wind emission from three star systems, illustrating a direct method to determine the mass-loss rates of late-type main-sequence stars.

The successful impact of NASA’s DART on Dimorphos, the moon of asteroid Didymos, has been analysed using advanced numerical simulations. The results reveal the asteroid’s low surface cohesion and rubble-pile structure, similar to what has been observed on asteroids Ryugu and Bennu.

Cosmic dust contains all the elements needed for life but has previously been considered too rare to have acted as a ‘fertilizer’ for prebiotic chemistry. Now, using a combination of astrophysical and geological models, it is revealed that cosmic dust could have gently accumulated on the surface of early Earth in sufficient quantities to promote the chemical reactions that led to first life.

Kepler-1625b-I and Kepler-1708b-I are the most noteworthy exomoon candidates to date. A new analysis of the available data comes to a different conclusion.

Binary neutron star mergers are complex to understand astrophysically. A small piece of the puzzle may now have been solved using a computationally intensive simulation to explain how short gamma-ray bursts can be launched by a magnetar engine.

In October 2023, astronomers, planetary scientists and biologists gathered in Kyiv for Ukraine’s first international astrobiology meeting, advancing science and crossing disciplinary borders in wartime.

The observed ‘radius valley’ — a dip in the distribution of exoplanet radii, which separates rocky super-Earths from larger sub-Neptunes — is at odds with current theories of planetary formation. New simulations that couple planet formation and evolution, and account for the orbital migration of planets that are largely composed of steam, are able to reproduce the valley feature.

The Lyman-α emission line of hydrogen should be absorbed and thus not seen from galaxies in the early Universe — and yet it is observed. Now detailed images from JWST coupled with magnetohydrodynamical simulations show that interactions between galaxies are facilitating the escape of this radiation.

High-mass stars in the Milky Way often exist in systems of two or more stars, but how this multiplicity arises is not clear and so far there have been no unequivocal observations of protostellar systems that could solve the issue. Now, systems of five, four and three stars, and several binaries, have been resolved in a star-forming region, and point to core fragmentation as the likely origin of multiplicity.

The size distribution of solid grains in dense clouds is a key parameter to constrain in order to understand grain growth, which influences the nature and timescale of the formation of protoplanets. A JWST study has quantified the grain size distribution by modelling the spectral absorptions arising from ice components of grains before protostellar collapse.

If advanced technological extraterrestrial lifeforms are out there, where are they? Thus goes the Fermi paradox. This Perspective reviews various solutions and proposes that they are either not there or are deliberately hiding from us.

On Earth, technological advances required open-air combustion, which needs an oxygen partial pressure of about 18%. This threshold can help guide searches for detectable technospheres on other planets.

The habitability of a planet is defined at a fixed time. A bigger challenge is to understand how that habitability is sustained over geological timescales, and how the underlying processes compare across different planetary bodies.