Articles in 2021

Understanding the progenitors of type Ia supernova is important for their use as cosmological distance probes. Here the authors identify a candidate for a type Ia supernova that is due to explode in 70 million years: a white dwarf in a binary system with a stripped core-helium-burning star.

By combining a repository for artificial intelligence models and a supercomputing cluster, an entire month’s worth of advanced LIGO data is analysed in just 7 min, finding all binary black hole mergers previously identified in this dataset and reporting no misclassifications.

The black holes in Galactic globular cluster Palomar 5 have been throwing their weight around and ejecting the stellar component of the cluster, creating its tidal tail and sparse appearance. Models predict that a billion years in the future the cluster will be composed entirely of stellar-mass black holes.

A sophisticated suite of cosmological simulations shows that the interplay between the growth of cold gas, which intrinsically varies due to halo assembly bias, and the feedback from active galactic nuclei can explain the observed bimodality in the colours of galaxies as a function of their halo mass.

Calculations of water activity reveal that this parameter can be a substantial barrier to habitability for clouds of Solar System planets. In particular, water activity within droplets of Venus’s clouds is more than 100-fold below the threshold for biotic activity of known extremophiles.

X-Ray diffraction data from the Curiosity rover found evidence of glauconitic clays, which are sensitive to the duration of sedimentary conditions within bodies of water. This result is indicative of a low-temperature aqueous environment that remained in a steady state for extended periods of time, favouring its habitability.

Three years of observations with the ExoMars TGO Atmospheric Chemistry Suite have clarified the mechanism of atmospheric water loss from Mars, and particularly the fraction of deuterium compared with hydrogen. Analysis of several isotopologues of water in the mid-atmosphere of Mars shows that atomic H and D are produced at perihelion in relative amounts controlled by photolysis. These atoms are able to escape from the atmosphere.

By stacking thousands of cosmic filaments and examining the velocity of galaxies perpendicular to the filament’s axis, it is shown that they display vortical motion consistent with rotation, signifying that angular momentum can be generated on unexpectedly large scales.

What is the origin of the methane detected in Enceladus’s plumes? A Bayesian approach to the problem shows that abiotic serpentinization of rocks cannot explain the methane abundance by itself, and biotic methane production gets the highest likelihood—provided the probability of life emerging at Enceladus is high.

Fine frequency structures of type III radio bursts are caused by the moving of intense clumps of Langmuir waves in a turbulent medium. Analysis of these structures can infer properties of the coronal and solar wind plasma and its density fluctuations.

Under the pressure of a watery ocean, rock-forming minerals might dissolve at a planet’s rock–water interface, generating a denser-than-water layer that should be incorporated into models. The experimental data for MgO presented here are relevant to water-rich Earth-sized planets such as TRAPPIST-1 c and f, and to Uranus.

A dust cloud in the line of sight towards supernova remnant RX J1713.7−3946—identified using Gaia data —contributes to the GeV gamma-ray emission of the region.

Kepler space telescope observations of 26 intermediate-mass rotating stars (slowly pulsating B-type stars) are analysed to isolate the gravity modes that probe the stars’ deep interiors. Internal mixing levels are unexpectedly varied and best reproduced with models incorporating radially stratified mixing profiles.

Spectropolarimetric observations of a solar pore at high temporal and spatial resolution identify the presence of magnetic field torsional oscillations. Simulations suggest that such oscillations are triggered by a photospheric kink mode, which can contribute substantially to upward energy transport within the solar atmosphere.

The detection of methanol—a molecule that primarily forms on the cold, icy surfaces of dust grains—in a warm protoplanetary disk is an indication that complex organic molecules are inherited from the interstellar medium and transported intact to planet-forming regions.

Radar measurements obtained between 2006 and 2020 determine fundamental parameters of Venus, including its spin axis precession, moment of inertia and amplitude of length-of-day variations. Observed length-of-day variations are attributed to approximately 4% changes in the atmospheric angular momentum.

Stars, including the Sun, dim suddenly in the extreme ultraviolet and X-rays in the aftermath of a flare, and most of the time this dimming coincides with a coronal mass ejection. Such a correlation provides insight into the atmospheric escape and habitability of exoplanets.

Main sequence stars older than the Sun have asteroseismically determined rotation rates that depart from standard age–rotation relations, showing support for the concept of weakened magnetic braking.

Data-driven workforce models predict that if the status quo is maintained, the fraction of women astronomers at all levels of academia will be below 30% for at least 60 years. Even if affirmative action were adopted, the gender gap would persist for another 25 years.

Laboratory experiments where meteorites are heated up to 1,200 °C are performed in order to inform on the outgassing from exoplanetary interiors. Differing considerably from assumptions commonly used by models, the experiments indicate that terrestrial planets would form water-rich steam atmospheres with substantial amounts of CO₂ and CO.