This week in cosmology brought advances in measuring cosmic expansion and observing the early universe, alongside theoretical refinements and new tools for understanding dark matter. A measurement using red giant stars as distance markers found the universe expanding at about 72 kilometers per second per megaparsec—higher than some other recent estimates—though scientists continue to grapple with disagreement between different measurement methods. The Simons Observatory's Small Aperture Telescopes in the Atacama Desert have begun operations and are performing better than expected, producing exceptionally clear images while searching for primordial gravitational waves from the early universe. On the dark matter front, simulations of galaxy formation show that the distribution of dark matter around galaxies of all sizes remains consistent with standard cosmological models, even when accounting for the effects of stellar explosions and radiation. A new real-time system called DETECT successfully identified transient events—including a superluminous supernova—by rapidly cross-referencing new alerts against spectroscopic data, finding roughly 15 percent of such events between 2020 and 2024. In stellar astrophysics, a survey of candidate carbon-rich stars found that most objects in the traditional color-selection box were actually oxygen-rich stars instead, revealing contamination in a distance measurement technique. Finally, researchers simulated how gravitational waves from neutron stars forming in the disks around black holes would appear to detectors, potentially opening a new way to study stellar collapse and compact object formation.
Researchers tracking metal-poor brown dwarfs with the James Webb Space Telescope found that about half originated in the Milky Way's thin disk while the other half came from the thick disk, halo, or were even captured from the dwarf galaxy that collided with our galaxy long ago, revealing how the galaxy assembled itself over time. A young star system showed dramatic changes in its planet-forming disk over just two years, with material flowing more slowly and becoming less abundant, apparently because the star was producing less heat to stir up the disk—a finding that may help explain how planets form around very young stars. New measurements of planets orbiting the young star V1298 Tau refined their masses, finding that the innermost planet is heavier than previously thought and confirming the system contains several giant planets despite the star being only about a billion years old. The interstellar comet 3I/ATLAS revealed an unusual volatile composition when observed with high-resolution spectroscopy, showing different gases at different times and suggesting its chemistry differs from typical solar system comets. Deep imaging of the debris disk around Beta Pictoris revealed that the structure called the Cat's Tail is made primarily of organic material dust grains, likely created by collisions between larger objects. Astronomers discovered that GJ3090 b is the first retrograde exoplanet orbiting an M dwarf—meaning it moves opposite to its star's rotation—and found no massive companion to explain this unusual orbit, suggesting the planet's strange motion is a remnant of its chaotic formation.
One observation this week revealed an unexpectedly mature galaxy at the distant universe's early stages: a massive galaxy observed when the universe was less than a billion years old shows evidence of having exhausted its star-forming fuel long ago, contradicting models of how such galaxies should develop. In a separate finding, researchers studying brown dwarfs in our Milky Way using the James Webb Space Telescope identified 23 low-metal brown dwarfs and traced their origins to different galactic components, including some likely accreted from the dwarf galaxy Enceladus during an ancient collision. Astronomers also compiled a unified, six-dimensional map of stars across the Milky Way using Gaia data, combining previously separate stellar catalogs to create a more accurate census of the galaxy extending to 250 kiloparsecs. Work on variable stars called Cepheids developed a new method for measuring cosmic dust obscuration by examining neighboring stars, refining the accuracy of distance measurements used throughout astronomy. Research into supermassive black holes found that relativistic jets are launched not from the thin accretion disk itself but from a thicker, hotter region that forms when the disk truncates at small radii, explaining how highly accreting black holes can produce powerful jets. Finally, astronomers discovered that fast radio bursts with persistent radio sources preferentially occur in hydrogen-poor superluminous supernova host environments, suggesting these bursts may originate from young, energetic stellar remnants in metal-poor galaxies.
This week in high-energy astrophysics brought discoveries spanning black hole physics, neutron stars, and stellar explosions. Researchers found that when a supermassive black hole's accretion disk—the swirling material feeding the black hole—becomes truncated or cut off at its inner edge, it triggers the launch of powerful relativistic jets of energy into space, solving a longstanding puzzle about how these jets ignite in highly feeding black holes. In a separate study of stellar dynamics around growing supermassive black holes, scientists determined that stars in galactic centers collide with each other at extremely high speeds (over 2,500 kilometers per second) with increasing frequency as the black hole grows, producing gravitational waves and powerful explosions. Astronomers analyzing a peculiar event called AT2019aalc concluded it represents a star being tidally disrupted by a black hole not once but twice, with dust obscuring the light from these violent encounters. In the realm of fast radio bursts, researchers discovered that repeating bursts originating from radio sources favor host environments similar to hydrogen-poor superluminous supernovae—rare, metal-poor galaxies—suggesting these bursts may arise from young, energetic stellar remnants. Finally, detailed modeling of a gamma-ray burst associated with a supernova revealed that a newly formed magnetar—an extremely magnetic neutron star—powers both a focused jet and a wider wind of energy that together shape the radiation we observe across multiple wavelengths.
This week in instrumentation and methods, researchers deployed new computational techniques to extract hidden signals from astronomical data. A convolutional neural network was developed to isolate the innermost photon ring around black holes from surrounding noise, enabling measurements of black hole spin that would otherwise be obscured. Separately, astronomers introduced a new method to detect small solar system objects in James Webb Space Telescope images by analyzing differences between consecutive exposures, improving sensitivity by a factor of about 1.4 and helping identify asteroids that approach Earth. On the simulation side, a faster planetary dynamics integrator called WHFast512 was rewritten in machine code to run over eight times quicker than its predecessor while maintaining extreme accuracy over billions of years of orbital calculations. New software tools were also released: EPIMETHEUS for characterizing how starlight spreads in telescope images when combining multiple observations, CERIDWEN for inferring the ages and compositions of stars across entire galaxies using graphics processors, and an updated version of the PLUTO code that simulates how gas and multiple dust species exchange heat in protoplanetary disks. Finally, the Simons Observatory's Small Aperture Telescopes in Chile began operations and are performing better than expected, detecting the universe's oldest light with exceptionally low noise across six frequency bands.
This week in solar and stellar astrophysics brought discoveries spanning the structure of our galaxy, the behavior of star systems, and the physics of stellar atmospheres. Using the James Webb Space Telescope, researchers identified 23 metal-poor brown dwarfs and traced their origins—finding that about half came from the galaxy's thin disk like our sun, while others originated in the thick disk, halo, or even arrived from the disrupted Sagittarius galaxy, offering new clues to how the Milky Way assembled itself. In a separate study of how stars' rotation affects their surroundings, detailed computer simulations showed that faster-spinning solar-type stars produce stronger stellar winds and create more powerful magnetic barriers around themselves, helping explain how rotation shapes a star's influence on nearby planets. A measurement of the binary system MWC 656 revealed an egg-shaped orbit with a period of about 60 days and suggests the companion object is nearly as massive as four suns, raising the possibility it may be a black hole. Meanwhile, observations of a young star's disk using infrared spectroscopy detected unexpected chemical changes over two years, including shifts in hydrocarbon emissions that may reflect drops in accretion—the flow of material onto the star—and could help explain how planetary systems form. Astronomers also discovered an old population of thin-disk stars that had previously been hidden among younger stellar populations, providing a new sample for studying the galaxy's early evolution. Finally, data from the Parker Solar Probe captured an unusual fast solar wind stream near the sun with turbulent properties unlike those typically observed, offering fresh insights into how solar wind acceleration works.