Volume 4 Issue 2, February 2020

The Crab Nebula, formed from a supernova recorded in 1054 ad, is the brightest object in the TeV (teraelectronvolt) gamma-ray sky. Measuring the extension of the gamma-ray nebula helps us to understand particle acceleration and interaction at the highest photon energies.

Accretion onto neutron stars can generate photon luminosities well in excess of the Eddington limit. Now it has been shown that it can also produce outflows with similar mechanical power, requiring a rethink of the interaction between accretion flows and neutron star magnetospheres.

Cosmology now has a standard model — a remarkably simple description of the Universe, its contents and its history. A symposium held last September in Cambridge, UK, gave this model a ‘health check’ and discussed fascinating questions that lie beyond it.

Extreme blazars emitting teraelectronvolt photons are ideal targets to study particle acceleration processes. The growing number of such sources has been critical for γ-ray cosmology, studying intergalactic magnetic fields and putting constraints on exotic physics.

SPHERE at the VLT observed Hygiea, the fourth largest body in the main belt and the parent body of a big asteroid family, at unprecedented spatial resolution. Its unexpected spherical shape without any impact crater is explained by numerical simulations with a big impact that fluidized the body, reassembling it in a rotational equilibrium regime.

ALMA observations have revealed a pair of symmetric spiral arms in the protostellar disk around HH 111 VLA 1. This discovery would seem to confirm hydrodynamical models that suggest that symmetric spiral structures arise in disks as a consequence of active accretion.

Diffuse X-ray emission is detected around an ultraluminous X-ray source, interpreted as a wind-powered expanding nebula. Its energetics suggests that a super-Eddington regime can be longer than the spin-up time of the central neutron star.

Thousands of compact and massive star clusters have formed at a steady rate over the past 1 Gyr around the central giant elliptical galaxy of the Perseus cluster, showing that progenitor globular clusters can form over cosmic history from cooled intracluster gas.

A highly magnified, strongly lensed star-forming galaxy is detected in X-rays. It is a low-mass, low-metallicity starburst that is a likely analogue to the first generation of galaxies, which may have played a role in reionizing the Universe.

An angular extension at gamma-ray energies of 52 arcseconds is detected for the Crab nebula, revealing the emission region of the highest-energy gamma rays; simulations of the electromagnetic emission provide a non-trivial test of our understanding of particle acceleration in the Crab nebula.

Idealized synchrotron emission, incorporating time-dependent electron cooling, can fit ~95% of all time-resolved spectra of single-peaked gamma-ray bursts. The presented analysis probes the microphysical processes operating within these ultra-relativistic outflows.

A series of four storms appeared on Saturn’s northern polar region in 2018, unusually close to each other in space and time. By their dimension and the energy needed to form them, they appear to be a hitherto unobserved kind of storm at Saturn, intermediate between the regional- and the global-sized ones.

Graur et al. present near-infrared light curves of five type Ia supernovae based on Hubble Space Telescope data that show plateaux at late times (>150 days) rather than the expected ‘infrared catastrophe’. The authors suggest that the year-long plateaux are produced by the scattering of ultraviolet photons.

The standard cosmological model assumes a flat Universe, but some model inconsistencies appear when curvature is allowed, as supported by the latest Planck Legacy 2018 power spectra. Is it time to consider new physics?

As the Solar Orbiter spacecraft is scheduled for launch this month, European Space Agency (ESA) and NASA Project Scientists provide an overview of this major ESA–NASA mission to the Sun.