Articles in 2019

A glitch experienced by the Vela pulsar in 2016 has been studied in detail, revealing a curious slowdown of the neutron star’s rotation immediately before the event, and confirming some theoretical predictions of neutron-star physics.

The measured magnetic field strengths of four close-in gas giant planets are reported, using a technique based on magnetic star–planet interactions. Values range from 20 G to 120 G, close to estimates based on planetary internal heat flux, but ~10–100 times larger than predicted by dynamo scaling laws.

Full cosmological hydrodynamical simulations employing modified gravity find that disk galaxies can form and their stellar properties are only mildly affected. Modified gravity leaves signatures on large-scale structure observable with the Square Kilometre Array.

Tamanini and Danielski show that LISA will be sensitive enough to detect (massive) exoplanets orbiting double white-dwarf systems using gravitational waves. This population of exoplanets cannot be probed by other means, and detections will reveal potentially significant numbers of planets in the Galaxy and Magellanic Clouds.

Fragkou et al. present multiple pieces of evidence for the association of planetary nebula BMP J1613-5406 with Galactic open star cluster NGC 6067. Stars in the cluster evolve off the main sequence at about 5 solar masses, suggesting that this planetary nebula had a massive progenitor and supporting theoretical predictions of the mass range of planetary nebula progenitors.

A stacked series of lithographed polymer disks could provide a lightweight and modular optics system for a future hard X-ray telescope, retaining the angular resolution of current telescopes, but improving on effective area.

The velocity gradient technique is used to measure the magnetic field orientations and magnetization of five low-mass star-forming molecular clouds, also finding that collapsing regions constitute a small fraction of the volume in these clouds.

Leveraging the precision of K2 and TESS, Bowman et al. have detected variability in galactic and Magellanic blue supergiants that is due to low-frequency gravity waves in their interiors.

A predominance of small grains (tens of nanometres in size) over larger grains and the corresponding near- to mid-infrared excess radiation from H ii regions around massive stars and supernovae has been difficult to explain. Hoang et al. propose a radiative torque disruption method for large dust grains that fits with the observational constraints.

A principal component analysis of Cassini’s infrared spectral maps of Titan reveals the main features of Titan’s equatorial surface, effectively removing the obscuring atmospheric effects. A 6,300-kilometre-long strip of exposed icy bedrock—uncorrelated with topography or measurements of the subsurface—is visible, surrounded by organic deposits.

Stellar streams are the outstretched remnants of globular clusters torn apart by tidal forces. A data-driven search method for identifying streams finds stream material from ω Centauri, the most massive globular cluster within the Milky Way.

Diurnal and seasonal temperature variations of comet 67P’s nucleus are monitored by Rosetta’s imaging spectrometer VIRTIS during two months in 2014. The nucleus appears thermally homogeneous, with the temperature fluctuations mainly controlled by self-heating and heliocentric distance.

Bathymetric radar measurements of several lacustrine features on Titan’s northern polar region were obtained during the last Cassini flyby in April 2017. These 100-m-deep and methane-dominated lakes are probably carved and replenished by local rainfall and regulated by subsurface flows.

The composition and characteristics of a C-rich clast within the LaPaz Icefield 02342 meteorite suggests that the clast is composed of materials related to comets and icy bodies. The clast probably formed in the outer Solar System, was transported inward and finally accreted into LaPaz’s parent body.

Low-mass, low-metallicity cool subdwarf stars are rare in the solar neighbourhood, and therefore their properties are not well constrained observationally. Here the authors report both a mass and radius determination of a cool subdwarf in an eclipsing binary system, providing a valuable data point.

The abundance of primordial black holes in the Galactic halo is constrained through their microlensing of stars in M31. Despite monitoring tens of millions of stars, only a single candidate event is found, providing stringent upper bounds on their abundance.

A coupled thermal, geophysical and dynamical simulation covering 4.5 Gyr of evolution of Saturn’s inner mid-sized moons shows that, with the possible exception of Mimas, they formed early in Saturn’s history. A complex game of resonances has impacted the four older moons, shaping their geology and interior.

By conducting chemical reactions involving a single pair of reactants within helium nanodroplets, Henning and Krasnokutski have measured the energetics of simple reactions relevant to astrochemistry. This approach allows the reaction pathways of surface reactions to be predicted with more accuracy than before.

Ultracompact stellar clusters in the Galactic Centre are likely to be major contributors to the Galactic cosmic ray flux in the multi-TeV energy range. Observations of the diffuse gamma-ray emission from the Galactic Centre and two young massive star clusters correlate with the cosmic-ray distribution.

Bennu’s surface presents evidence of a variety of particle sizes, from fine regolith to metre-sized boulders. Its moderate thermal inertia suggests that the boulders are very porous or blanketed by thin dust. Bennu’s boulders exhibit high albedo variations, indicating different origins and/or ages.