Swallowed Worlds: How a Lost Hot Jupiter May Have Spun Up Kepler-56
Takato Tokuno’s study suggests that the red giant Kepler-56’s rapid rotation and misaligned core and envelope likely result from swallowing a hot Jupiter. Simulations show that its two known planets cannot provide enough angular momentum, but an engulfed giant planet could. This makes Kepler-56 a strong candidate for a star whose unusual spin reveals evidence of past planetary engulfment.
A Hidden River of Stars: Discovering a Stellar Stream Around Galaxy M61 with the Rubin Observatory
Astronomers led by Aaron Romanowsky used the Vera C. Rubin Observatory to discover a faint, 50,000-light-year-long stellar stream around the spiral galaxy M61. The stream likely formed from a dwarf galaxy torn apart by M61’s gravity, possibly triggering its starburst and active nucleus. This finding previews Rubin’s ability to reveal countless faint galactic remnants, deepening understanding of galaxy growth and evolution.
Tracing the Origins of the Universe’s Heaviest Elements: The R-Process Alliance Examines Ten Ancient Stars
Racca et al. (2025) studied ten ancient, r-process-enriched stars to uncover how the universe creates its heaviest elements. Using high-resolution spectroscopy, they found nearly identical abundance patterns across stars from distinct origins, with minimal variation (<0.1 dex). This surprising uniformity suggests that r-process nucleosynthesis, likely from neutron-star mergers or similar extreme events, follows a consistent, universal mechanism throughout cosmic history.
Tracing Planet Formation Through Stellar Fingerprints: A Spectroscopic Look at C/O Ratios in Directly Imaged Exoplanet Hosts
Baburaj et al. conducted a high-resolution spectroscopic survey of five stars hosting directly imaged exoplanets to measure their elemental abundances. They found solar-like C/O ratios for HR 2562, AB Pic, and YSES 1, but significantly sub-solar ratios for PZ Tel and β Pictoris. These differences suggest diverse formation environments and highlight how stellar chemistry can trace planet formation processes.
Relics of the First Galactic Core: How the Milky Way’s Oldest Stars Reveal Its Fiery Beginnings
Sun et al. map over five million metal-poor stars to uncover the Milky Way’s earliest structure. Using both observations and simulations, they find that the Galaxy’s oldest stars likely formed during high-redshift gas “compaction” bursts over 12 billion years ago. These events created a dense, non-rotating core, the proto-Galaxy, that later evolved into the Milky Way’s central bulge and thick disk.
Barium Clues: Unraveling the Origins of Carbon-Enhanced Ancient Stars
Sitnova et al. studied ten carbon-enhanced metal-poor stars to measure their barium isotope ratios. They found that CEMP-s stars have isotope patterns consistent with the slow neutron-capture (s-) process, while CEMP-rs stars show signatures matching the intermediate (i-) process. This distinction suggests that the i-process, rather than a mix of s- and r-processes, shaped the chemical makeup of many CEMP-rs stars.
Tracing the Chemistry of Exoplanet Hosts: What K2 Stars Reveal About Planets and Their Parent Stars
Loaiza-Tacuri et al. analyzed 301 K2 exoplanet-hosting stars using high-resolution spectra to measure stellar temperatures, metallicities, magnesium abundances, and activity levels. They confirmed the planetary radius gap near 1.9 R⊕, found that larger planets orbit more metal-rich stars, and showed stellar activity decreases with planet size. Most hosts belong to the Galactic thin disk, linking stellar chemistry to planetary formation.
Tracing the Ghosts of Clusters: StarStream Reveals Hidden Stellar Streams in the Milky Way
Yingtian Chen and colleagues used their new algorithm, StarStream, to uncover 87 stellar streams from globular clusters in Gaia data, doubling the known number. The method detects even irregular, misaligned streams, revealing that many clusters are actively losing stars. Measured mass loss rates show that low-mass, extended clusters like Palomar 5 are nearing tidal disruption, offering fresh insights into the Milky Way’s evolution.
Uncovering the Chemical Story of Star-Birth Rings in Nearby Galaxies
Eva Sextl and Rolf-Peter Kudritzki use MUSE data to study four spiral galaxies with bright nuclear star-forming rings. By separating young and old stellar populations, they find that these rings are metal-rich, not metal-poor as once thought. Their new “physical metallicity” method reveals that inflows of fresh gas and repeated star formation cycles drive long-term chemical enrichment in galactic centers.
Tracing Saturn’s Watery Past: JWST Detects Heavy Water on Saturn’s Moons
Using JWST, Brown et al. detected deuterated water (heavy water) on Saturn’s icy moons, finding D/H ratios about 1.5 times higher than Earth’s oceans. This consistency across moons suggests they formed from the same cold, unprocessed ices, not from a hot gas disk. The results rule out earlier claims of extreme D/H on Phoebe and provide new insight into how Saturn’s satellites and solar system ices formed.
Mapping the Life and Legacy of Dying Stars: How Planetary Nebulae Reveal the Milky Way’s Chemistry
N. Erzincan and colleagues analyzed 1,449 planetary nebulae to explore how dying stars shape the Milky Way’s chemistry. Using spectra from the HASH database and Gaia distances, they measured temperatures, densities, and elemental abundances. Disk nebulae were richer in heavy elements than those in the halo, and sulfur and nitrogen showed a strong correlation, revealing links between stellar evolution and Galactic chemical enrichment.
Hunting for Dusty Trails: Ten New Exocomet Transits Discovered in Kepler Data
Using a neural network trained on simulated comet transits, P. Dumond and colleagues reanalyzed Kepler’s light curves and discovered ten new exocomet transits among 17 high-confidence detections. Their machine learning approach efficiently separated real signals from noise and revealed that exocomet activity occurs around both young and old stars, suggesting cometary systems may remain active throughout stellar lifetimes.
Unraveling Nephele: The Hidden Galaxy Behind Omega Centauri
Pagnini et al. (2025) reveal that Omega Centauri was once the core of a vanished dwarf galaxy named Nephele. Using stellar chemistry and motion data from APOGEE, they identify hundreds of stars once belonging to this system. Their findings suggest Nephele’s remnants form extended stellar streams, showing how the Milky Way grew by merging with smaller galaxies.
Mapping Metal and Molecule Mysteries in Interstellar Comet 3I/ATLAS
Hoogendam et al. (2025) used the Keck Cosmic Web Imager to study interstellar comet 3I/ATLAS, confirming gas emissions from cyanogen (CN) and nickel (Ni). They found Ni concentrated closer to the nucleus, suggesting it originates from short-lived compounds like metal carbonyls or organics. The findings indicate that interstellar comets may be metal-rich but water-poor, offering clues about the chemistry of distant planetary systems.
Tracing Starlight: How Ultraviolet Observations Reveal the Heavy Elements in HD 196944
Roederer et al. used ultraviolet spectra from the Hubble Space Telescope to study HD 196944, a carbon-enhanced metal-poor star rich in s-process elements. They detected 35 heavy elements, the most ever found in such a star, and showed these likely came from a former AGB companion. Their results confirm that UV spectroscopy can reveal new details about how stars create the universe’s heaviest elements.
Liller 1: A Galactic Mystery, Uncovering the Origins of a Massive Star Cluster in the Milky Way’s Heart
Anna Liptrott and colleagues used APOGEE data to study whether Liller 1 helped form the Milky Way’s bulge. By comparing its chemical makeup with stars from the bulge and disk, they found that Liller 1’s α-element abundances differ significantly, showing it’s chemically distinct. The results rule out it being a major bulge “building block,” suggesting instead that Liller 1 is a minor or possibly extragalactic remnant.
Unearthing a Disequilibrium: JWST Unveils Methane and Carbon Monoxide in 51 Eridani b
Using JWST’s NIRSpec, Madurowicz et al. directly detected methane and carbon monoxide in the atmosphere of the exoplanet 51 Eridani b, confirming chemical disequilibrium caused by atmospheric mixing. Their high-resolution spectra revealed a 4.8σ planetary signal and an atmosphere that is partly cloudy, metal-rich, and about 800 K. This marks JWST’s first direct confirmation of multiple molecules in a cool, Jupiter-like exoplanet.
A Star from Another Galaxy: The Most Pristine Relic of the Early Universe
Astronomers led by Alexander Ji discovered SDSS J0715−7334, the most metal-poor star ever found, originating from the Large Magellanic Cloud. Its composition suggests it formed from gas enriched by a single massive Population III supernova, revealing how early stars seeded the universe with heavy elements. This discovery provides a rare local glimpse into the universe’s first generations of stars.
Mapping the Hidden Streams of the Milky Way: Correcting Bias in Dark Matter Searches
Boone et al. (2025) develop a method to correct biases in stellar stream observations caused by uneven survey conditions in the Dark Energy Survey. Using synthetic stars from the Balrog tool, they refine measurements of stellar densities, demonstrating the method on the Phoenix stream. Their corrections remove false patterns and improve dark matter studies, offering an essential approach for future deep surveys like LSST.
Bars Across Time: Tracing Galactic Structures Over 12 Billion Years
Using JWST data, Zoe Le Conte and collaborators traced how stellar bars in disc galaxies evolved over 12 billion years. They found the bar fraction declines from 16% at z ≈ 1–2 to 7% at z ≈ 4, showing that stable discs already existed early in cosmic history. Bar lengths stayed roughly constant, indicating that bars and galaxy discs have grown together over time.