Volume 3 Issue 8, August 2019

Besides supernovae, few astrophysical processes can release close to 10⁵¹ erg of energy. A growing number of stellar outbursts are now recognized to have energy releases matching those of faint supernovae. These transients can be triggered by various mechanisms, and their discrimination is sometimes a tricky issue.

Machine learning and related methods will be crucial for automatically classifying transients as they happen in order to best allocate follow-up resources. Such techniques cannot be used off the shelf, but must be developed by the community as a whole.

Astronomers using the Zwicky Transient Facility have discovered two white dwarfs orbiting each other every 6.9 minutes. But there is nothing transient about the gravitational waves emitted from this binary: the stars will produce persistent ripples in spacetime for millennia.

The interstellar medium in our Galaxy is threaded by magnetic fields. A new method of inferring magnetic field directions from spectroscopic measurements of this turbulent medium provides insight into the role of these magnetic fields in molecular cloud formation and evolution.

The report of a 10,000 solar mass black hole in a dwarf galaxy provides new clues about how supermassive black holes form and grow with their host galaxies.

The latest observational developments in the fast-paced fields of superluminous supernovae and fast blue optical transients, both types of extreme supernovae, are reviewed. The next decade, with the advent of survey facilities such as the Large Synoptic Survey Telescope, will deliver many more examples of such objects.

Thermonuclear supernovae — those involving the explosion of a white dwarf — and particularly type-Ia supernovae, have become indispensable tools for observationally measuring the expansion of the Universe. However, we still do not fully understand these objects, especially the range of progenitor systems that give rise to them. Future observations will enable us to make headway.

The diversity of core-collapse supernovae — the explosions of massive stars — has increased greatly recently, driven by developments in observing facilities and techniques. Here Modjaz, Gutiérrez and Arcavi survey the current observational classifications, question whether the lines are starting to blur and look forward to the large samples of supernovae that are to come.

A minor but important fraction of silicate stardust believed to come from red giant stars is shown to have a supernova origin instead, making the supernova dust fraction among >200-nm-sized presolar silicates significantly higher than previously inferred.

A systematic change in Jupiter’s magnetic field can be detected by collating all data obtained in the last 45 years by multiple spacecraft, from Pioneer 10 to Juno. Such variation can be attributed to the zonal winds, which advect the magnetic field from the deep atmospheric layers.

Measurements of Mo in meteorites constrain the time when the Earth accreted carbonaceous material from the outer Solar System (a likely source of Earth’s water and volatiles) to late in the Earth’s growth history—probably in the same event that formed the Moon.

Chandra X-ray Observatory spectral observations of the active star HR 9024 provide evidence of plasma motions that indicate a stellar flare and subsequent coronal mass ejection. This event provides critical information on non-solar coronal mass ejections and a point of comparison to the Sun, a much less active star.

Two Hα emission peaks are detected within the disk of the T Tauri star PDS 70: one corresponds to protoplanet PDS 70 b, and the other is associated with a second accreting planet of few Jupiter masses at ~35 au. The two protoplanets are near 2:1 mean motion resonance, supporting migration scenarios of giant planets during planetary formation.

An exceptionally low delay of 83 minutes between variability in the accretion disk and Hα emission is reported from the nucleus of the dwarf galaxy NGC 4395. The implied black hole mass of about 10,000 solar masses is consistent with the mass–velocity dispersion relation.

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.

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.

The Faint Intergalactic medium Redshifted Emission Balloon (FIREBall-2) is an ultraviolet multi-object spectrograph mission designed to observe the faint gas surrounding z ≈ 0.7 galaxies from the very top of the Earth’s stratosphere, explains Project Scientist Erika Hamden.