First Exomoon Search via Astrometry
A team led by Quentin Kral used the VLTI/GRAVITY interferometer at ESO's Very Large Telescope to test an astrometric method for detecting exomoons — moons orbiting planets outside the Solar System. By tracking the motion of the brown-dwarf companion HD 206893 B, the researchers spotted small but systematic wobbles in its position on the sky.
These wobbles are consistent with a companion moon of about 0.4 Jupiter masses, though the object remains a candidate pending confirmation from further observations. The key result is that astrometry can detect exomoons as small as Neptune. The same technique will next be applied to two other substellar companions, AF Lep b and β Pic b.
Spiral Galaxies "Leaking" Ultraviolet Into Space
In the AstroSat UV Deep Field South survey, astronomers Soumil Maulick and Kanak Saha detected escaping Lyman continuum radiation from three massive spiral galaxies (stellar mass above 10 billion solar masses) at a redshift of roughly z≈1 — the first solid detection of such leakage from well-characterized disk galaxies at high redshift.
All three systems are seen nearly face-on, hinting that a disk's orientation may influence whether the escaping radiation is detected. Two of the three galaxies host active galactic nuclei, complicating the interpretation. The finding matters for understanding cosmic reionization, when ultraviolet light from galaxies ionized intergalactic gas and made the Universe transparent.
How Spiral Arms Turn Gas Into Stars
Researchers traced the life cycle of molecular clouds in two grand-design spirals, NGC 4321 and M51, using tracers of molecular gas (CO), dense gas (HCN), and star formation (Hα, 24 μm) at matched resolutions of 270 and 125 parsecs. The analysis followed gas as it moved across the spiral arms, from the upstream to the downstream side.
In NGC 4321, the HCN/CO and SFR/HCN ratios steadily rise deeper into the arm, meaning gas density and star-formation efficiency both increase along the way. In M51 the trend is weaker. The result supports density-wave theory: spiral arms genuinely compress gas, driving a sequence from diffuse clouds to newborn stars.
What Happens When White Dwarfs Merge
Kyle Kremer and colleagues modeled the merger history of binary white dwarfs across the Milky Way, combining the COSMIC population-synthesis code with a star-formation history derived from FIRE-2 galaxy simulations. The work produced public catalogs of possible outcomes — from AM CVn binaries and R Coronae Borealis stars to Type Ia supernovae and millisecond magnetars.
The outcome depends on the masses and chemical composition of the merging white dwarfs. The study gains extra relevance ahead of the LISA gravitational-wave observatory, which will detect signals from tens of thousands of close white dwarf pairs in our Galaxy, offering a direct test of the model's predictions.
Gravitational Waves Tell About the Universe's First Moments
A team led by Debtosh Chowdhury analyzed the 15-year NANOGrav dataset, which tracks millisecond pulsars in search of a stochastic gravitational-wave background. The researchers used this signal to constrain parameters of inflation — the era of extremely rapid expansion just after the Big Bang — as well as the temperature and equation of state of the subsequent reheating period.
The analysis favors an unusually blue-tilted tensor spectrum (nt = 2.20) and suggests the early Universe's vacuum may not have been the standard Bunch-Davies vacuum but a so-called alpha-vacuum. If confirmed, this would be a trace of new physics operating in the Universe's first moments.
