Reviews & Analysis

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.

A low atmospheric carbon abundance can be a ‘habiosignature’ and indicate the presence of substantial surficial liquid water, tectonic activity and/or a biomass in temperate rocky exoplanets. It can potentially be detected by JWST at 4.3 μm in a few tens of transits.

A model investigating the build-up of the atmosphere of Venus shows that it could have originated from a vigorous phase akin to plate tectonics during the first billion years of its evolution.

Measurements of Jupiter’s gravity by the Juno mission have established that the winds extend 3,500 kilometres below the surface. Cylindrically oriented zonal flows provide the best match in a new model using gravity harmonics up to degree 40.

Periodic sub-structure in radio emission from magnetars provides an observational link not only between magnetars and fast radio bursts, but across all classes of radio-emitting rotating neutron stars. The correlation between sub-structure periodicity and neutron-star rotational period can be used to determine an underlying period for fast radio bursts.

The optical properties of the organic hazes that form in water-rich exoplanet atmospheres differ from those that form in nitrogen-rich atmospheres. This difference in optical properties can have an observable effect on spectral observations of exoplanets and could impact the interpretation of current and upcoming JWST observations.

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.

Theories predict that core asphericity must be involved in core-collapse supernova explosions; however, the shape of these explosions has not been directly observed. The distribution of the explosive burning ash has now been revealed using nebular spectroscopy, indicating that a collimated structure is common in many stellar explosions.

High-resolution observations using a network of ground-based radio dishes and one telescope in space have revealed filamentary structures in the source 3C279. These filaments may explain the origin of radio variability in blazar jets.

Fast radio bursts, arriving at Earth from distant galaxies, usually have durations of a few milliseconds or more. Now, data on a source of repeating fast radio bursts have been revisited, with much higher time resolution than before, and burst signals are seen that last only a few microseconds — showing that the properties of fast radio bursts are more diverse than previously thought.

JWST observations of Jupiter reveal a narrow and intense atmospheric jet at the equator of the planet, close to its tropopause. The jet is manifest in the fast motions of equatorial hazes and is most likely a deep counterpart of the equatorial oscillations observed in Jupiter’s stratosphere.

Giant impacts can hit Venus harder than Earth in the end stages of planetary formation, super-heating Venus’s core. Slow escape of that heat drives long-lived surface volcanic activity.