Cold gas survives merging galaxy's outflows
Using JWST/MIRI-MRS and ALMA, astronomers studied the distribution of molecular gas in the nearby (z=0.0429) ULIRG IRAS20551-4250, a galaxy in the late stages of a merger. VLT/MUSE data revealed powerful ionized [O III] outflows reaching 790 km/s, yet their mass outflow rate is tiny, less than 0.01 solar masses per year, and no outflows are seen in either molecular gas phase.
The observations show warm hydrogen (500-1400 K) heated by ultraviolet radiation from the nucleus, while cold CO gas dominates, accounting for over 95% of the total molecular mass. Velocity maps reveal tidal tails and disturbed kinematics typical of a late-stage merger. Overall, the findings suggest the observed outflows are insufficient to halt star formation or shut down the galaxy.
SHINE survey characterizes 460 stars
SHINE (SPHERE INfrared survey for Exoplanets), the second-largest direct-imaging exoplanet survey to date, observed 460 stars between 2015 and 2023 under ESO's guaranteed time at VLT/SPHERE. In this final paper of the series, researchers homogeneously determined stellar properties across the whole sample - ages, masses, and binarity - combining kinematic indicators, lithium abundance, rotation, activity, and isochrone fitting.
A thorough vetting for stellar companions using astrometric, spectroscopic, and imaging data yielded a subsample of 333 stars, spanning a wide range of ages and masses. This curated sample of young single hosts will serve as the foundation for the survey's final statistical analysis of exoplanet occurrence rates.
Possible exomoon around a brown dwarf
Astronomers found signs of a companion around the brown dwarf CD-35 2722 B, itself orbiting a star and one of the rare substellar objects imaged directly. Applying the radial-velocity technique - the same method that discovered the first exoplanet around a Sun-like star back in 1995 - to CRIRES+/VLT spectra, the team detected a periodic signal consistent with a body of minimum mass around 0.9 Jupiter masses and an orbital period of roughly 170 days.
Since the companion orbits a brown dwarf rather than a planet, there is no formal term for it, so the researchers use the neutral label "exomoon candidate." Despite more than 6,000 confirmed exoplanets, no exomoon has ever been confirmed - only disputed candidates exist. The finding shows that the refined technique can now probe even lower-mass companions, bringing astronomers closer to an unambiguous first detection.
MAVEN explains Martian auroras' origin
NASA's MAVEN mission found that some types of Martian auroras form through the same mechanism as Earth's: charged particles from the solar wind funnel along magnetic field lines into the atmosphere and excite gas molecules to glow. This is surprising because Mars lacks a global magnetic field, having only patchy magnetized regions of crust, making the resemblance to Earth's process unexpected.
These auroras are linked to the ongoing loss of the Martian atmosphere: during solar storms, charged particles strip away the planet's upper gas layers. Understanding this connection helps researchers reconstruct how Mars transformed from a once wet, thick-atmosphere world into the thin, cold planet it is today.
Measuring Sgr A*'s spin with star S301
The discovery of star S301, with a pericenter of just 280 gravitational radii and an eccentricity of 0.9825, opens a path to measuring the spin of the supermassive black hole Sgr A* through Lense-Thirring precession - an orbital nodal shift caused by the black hole's rotation. The main challenge is Newtonian confusion: any non-spherical mass distribution around the black hole can also produce nodal precession, mimicking the relativistic signal.
The researchers show that stars with apocenters similar to S301 but much larger pericenters - notably S2, S55, and S38 - experience comparable Newtonian torques while carrying a relativistic signal up to 30 times weaker than S2's. This makes them useful calibrators for subtracting the background mass contribution. With continued GRAVITY+ astrometry and future ELT spectroscopy, the in-plane component of Sgr A*'s spin could become measurable within the coming years.
