Letters in 2017

Mapping the optical emission of a galaxy cluster to its mass is challenging. Lensing of the cosmic microwave background by massive clusters is used to calibrate the optical richness of clusters to their total baryonic mass at the ten per cent level.

The origin of the broad-line emission from type-1 active galactic nuclei is unclear. Calculations of emission lines from dusty clumps that are tidally disrupted by the central black hole suggest that these clumps give rise to the broad-line emission.

The relatively unexplored southwestern region of the Large Magellanic Cloud is host to a massive, embedded star-forming complex that rivals the star-forming efficiency of 30 Doradus. Its most luminous object could be a super star cluster in formation.

Chloromethane (CH3Cl) has been observed towards a low-mass protostar and comet 67P, making it the first organohalogen detected in space. The species was previously considered to be a biomarker, but the authors suggest viable alternative abiotic formation routes.

Optical pulsations from a millisecond pulsar that had transitioned from a rotationally powered regime to an accretion disk state have been detected. The optical emission is likely to be due to electron synchrotron emission in a rotation-powered magnetosphere.

The polarization resulting from electron scattering in a stellar atmosphere has been detected towards the rapidly spinning star Regulus. Deformation of the star from spherical allows this effect to be seen, fulfilling a prediction from around 50 years ago.

A candidate intermediate-mass black hole is reported within a molecular cloud near Sgr A*, the centre of our Galaxy. High-resolution observations with ALMA reveal extreme gas kinematics and a compact source consistent with a quiescent black hole.

A tight correlation between gamma rays and optical emission in nova ASASSN-16ma indicates that the optical light comes from reprocessed emission from shocks in the ejecta, rather than an energy release near the hot white dwarf, as in the standard model.

The detection and characterization of a large-scale ordered magnetic field through a gravitational lens in a galaxy beyond the local volume allows us to elucidate how such magnetic fields come about, supporting a mean-field dynamo origin.

Recent observations reveal tension between various cosmological probes. Assuming dark energy to be non-constant, depending on redshift, may relieve this tension. The Dark Energy Spectroscopic Instrument survey will be able to confirm this result.

Brightness changes of the Sun over timescales from minutes to decades, relevant to Earth’s climate and the detection of exoplanets around Sun-like stars, can be fully and precisely explained by the magnetic field and granulation of the Sun’s surface.

Diamonds precipitate from methane under the intense pressures of the atmospheres of Neptune and Uranus. Here, a laser shock experiment on a hydrocarbon sample shows that diamonds may require ten times as much pressure to precipitate as was previously thought.

The stardust component of interstellar dust has been quantified by analysing samples of pre-solar dust grains from meteorites and found to be at least twice as much as had been thought. The silicate portion follows the size distribution of interstellar dust.

Some star clusters in the Large Magellanic Cloud have extended main-sequence turnoffs, suggesting that the component stars have different ages. However, if the blue main-sequence stars were initially spinning rapidly, and experienced braking, the apparent age difference disappears.

M dwarfs harbour stellar dynamos driven by convective motions in their interiors. Previously, the magnetic field strengths generated by these dynamos were thought to saturate at 4 kG, but this limit has now been busted by four stars with dipole dynamo states.

Venus Express wind measurements at Venus’s cloud top during the night show a different picture than dayside. Both fast and slow motions are detected (there are only fast ones during the day) as well as many stationary waves related to surface relief.

Most of the Mars Trojans — asteroids co-orbiting the planet — are dynamically related; thus, they have a common origin. Joint information from spectral observations and dynamical modelling suggests that they were ejected from Mars itself after an impact.

Multiple stars are thought to form either through disk fragmentation or turbulent fragmentation, but the latter has had no clear observational confirmation. Here the authors report misaligned disks around a wide-binary pair, a sign of turbulent fragmentation.

Combining studies of star formation rates with studies of cloud–magnetic field alignment has revealed that magnetic fields are a primary regulator of star formation. Perpendicular alignment inhibits star formation, whereas parallel alignment facilitates it.

Low-mass black holes that accrete stars from locally dense environments grow over the Hubble time above a minimal mass of 10⁵ solar masses, independently of their initial mass. This explains why there are no convincing cases of intermediate-mass black holes to date.