This week in cosmology brought advances on multiple fronts, from new methods for measuring dark energy to fresh insights on long-standing tensions in cosmological measurements. Researchers proposed using the accumulated imprints of cosmic expansion encoded in gravitational waves—a phenomenon called integrated cosmological memory—as a way to constrain dark energy using "dark sirens," neutron star or black hole mergers whose distances can be inferred without electromagnetic observations. On the measurement side, a reanalysis of megamaser galaxies using improved velocity field reconstructions found a lower expansion rate than traditional methods yield, suggesting that discrepancies between different expansion rate measurements may stem from systematic errors in the older "Hubble ladder" rather than new physics. Several studies examined whether dark energy might be decaying over time or whether gravity itself operates differently than Einstein's theory predicts; while some hints of such effects appear in current data, the evidence remains inconclusive and awaits more precise measurements from upcoming surveys. In the early universe, new analysis of 21-centimeter radio signals showed that static galaxy population models can partially mimic the signatures of evolving populations, meaning improved observations combining global signals and local fluctuations will be needed to determine which picture is correct. Finally, researchers demonstrated that simulation-based inference methods can efficiently handle the enormous datasets expected from next-generation gravitational wave detectors like the Einstein Telescope, rivaling traditional Bayesian approaches while scaling better to larger sample sizes.
This week in exoplanet and planetary science brought discoveries across multiple scales of the solar system and beyond. Observations of the potentially hazardous asteroid 2001 WN5 ahead of its 2028 close approach to Earth revealed its rotation period, spectral type, and reflectivity, providing crucial characterization data for this near-Earth object. A new analysis of hot Jupiter atmospheres demonstrated how observations across multiple wavelengths (called phase curves) can constrain atmospheric circulation patterns, with sharp instruments potentially able to detect signatures of atmospheric winds rising and falling through clouds. In the outer solar system, detailed study of the binary centaur objects Typhon and Echidna revealed that Typhon's irregular, asymmetrical shape drives non-standard orbital dynamics between the pair. Meanwhile, researchers used computer simulations to show that forming moons around close-in rocky planets faces a significant bottleneck: stellar gravity makes it difficult for moon-forming material to persist after planetary collisions, except in rare cases where impacts occur in favorable directions. On Jupiter's moon Callisto, James Webb Space Telescope observations uncovered a striking bullseye pattern of water ice on the trailing hemisphere and identified carbon dioxide concentrated near impact craters Lofn and Heimdall, though the coexistence of solid and gaseous CO2 remains puzzling. Observations of the protoplanetary disk around star d216-0939 pinpointed water ice abundance at 5–6% on one side of the disk, suggesting outward material transport preserves ice in the outer regions.
This week in galaxy studies, astronomers discovered three new ultra-compact binary star systems where two stars orbit each other extremely closely in just minutes, found to contain helium rather than hydrogen, suggesting they may be far more common in the galaxy than previously thought. Observations of the active galaxy NGC 5548 using X-ray data revealed four distinct types of high-speed outflows with speeds up to 2,730 kilometers per second, with a newly mapped structure showing how wind strength varies with temperature. A large survey examining how galaxy environment affects their properties found that galaxies in clusters form stars less actively than isolated galaxies, though the effect depends on how frequently they orbit within the cluster, while galaxies hosting supermassive black holes show no such environmental dependence. Computer simulations combining the effects of supermassive black holes and stellar explosions showed that both processes work together to regulate the temperature of hot gas in galaxies, with black hole feedback dominating in the largest systems. Researchers identified nine candidate hypervelocity stars—ancient, metal-poor stars moving fast enough to escape the Milky Way—by measuring distances to over 41,000 stars using spectroscopic and position data. A new atlas containing 1,154 simulated galaxies across ultraviolet to submillimeter wavelengths provides a tool for testing theories of galaxy evolution and comparing simulations with real observations. Investigation of radio sources in a deep survey detected over 5,700 sources and characterized the diffuse radio glow from the galaxy using measurements at multiple frequencies.
Astronomers discovered three new ultra-compact binary systems where white dwarfs and neutron stars orbit each other extremely closely, completing their dance in under 30 minutes. Using X-ray observations of the active galaxy NGC 5548, researchers identified four distinct types of high-speed winds flowing outward from the region around its central black hole, with some reaching speeds exceeding 2,700 kilometers per second and revealing unexpected patterns in how wind strength varies with temperature. New computer simulations show that the rotation speed of neutron stars significantly affects how often and how powerfully they produce Type I X-ray bursts, with rapid rotation making bursts happen more frequently but with less intensity. Detailed observations of the binary system Her X-1 during eclipses revealed that ionized iron winds flowing from the neutron star persist even when its companion star blocks the direct radiation, indicating the wind originates from within the neutron star's immediate environment at speeds around 200 kilometers per second. Re-analysis of archival data from the microquasar SS 433 suggests that particles in its jets receive their primary acceleration near the jet's launching point, though additional acceleration throughout the jets is needed to explain the extremely high-energy radiation recently detected by ground-based observatories.
Radio astronomers this week deployed a new tool to clean up their data, demonstrated precise methods for comparing stellar simulations to observations, and advanced designs for future searches of distant life. A machine-learning system called MARS identified and removed radio interference from space signals while preserving 97% of real astronomical data and processing information up to 6 or 7 times faster than competing methods. A new software module called Custom Colors calculates how distant stars would appear through different telescopes by running stellar evolution simulations; when tested on six types of stars, its results matched observations from actual observatories with high accuracy. Looking further ahead, researchers proposed an array of 900 space telescopes equipped with spectrographs—instruments that split light into component colors—to search for atmospheric signatures of life on distant planets, and outlined how a specialized telescope could hunt for planets in binary star systems by measuring their gravitational wobble with unprecedented precision. More immediately, the James Webb Space Telescope continues surveying exoplanet atmospheres to identify which worlds might harbor life, though one detailed study found that stellar activity on the star TRAPPIST-1f would make detecting water vapor in that planet's atmosphere difficult even with about 50 observations, while carbon dioxide could be confirmed with roughly 10 observations.
This week in stellar astrophysics brought discoveries across multiple types of stellar systems and explosive events. Astronomers found three new ultra-compact AM CVn binaries—pairs of stars orbiting so closely they complete a dance in under 30 minutes—and used these discoveries to estimate that such systems are more common than previously thought, with roughly 2 to 5 percent of all their kind hiding in the galaxy. In a separate study, researchers resolved competing interpretations of the star HD 249179 by tracking its behavior over several years and concluded it is a classical Be star with a rotating disk, rather than the exotic high-energy object it sometimes appeared to be. On the explosive end, theoretical work on magnetorotational supernovae—the violent collapse of massive spinning stars with intense magnetic fields—showed that the nuclear composition of stellar material significantly alters the resulting blast's light, sound, and gravitational waves, offering a way to probe what lies inside stars through their final explosions. A new analysis of Type I X-ray bursts from neutron stars revealed that rapid rotation plays a major role in these events, making bursts more frequent but less powerful than models assuming non-rotating stars predicted. Finally, a search through over 41,000 metal-poor giant stars identified nine candidates for hypervelocity stars—objects moving fast enough to escape the Milky Way—potentially originating from the galactic disk or the Sagittarius star stream.