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A rendering of an orange and grey planet against a dark background.

What can some neon trapped in a chunk of rock tell us about Earth’s formation and the protosolar nebula? Quite a lot, as detailed in a recent study in The Planetary Science Journal.

Noble Mysteries

By analyzing rocks pulled from mid-ocean ridges, geologists have concluded that there are tiny amounts of noble gases in the deep interior of Earth. That’s a strange statement upon reflection: how did these gases, which are famously apathetic to essentially all other elements, end up embedded within rocks thousands of kilometers underground? Since their passivity rules out the potential of a chemical reaction that formed them in place, they must have been in the mantle since the very beginning of Earth’s history.

A map of Earth with the continents shown normally but the sea colored according to age.

A map illustrating the age of the seafloor. Mid-ocean ridges stand out clearly in red. By sampling material from these ridges, planetary scientists can infer the composition of Earth’s deep interior. Click to enlarge. [Mr. Elliot Lim, CIRES and NOAA/NCEI]

There are a few scenarios for how this could have happened. Though it’s possible that these inert species were delivered to the early Earth encapsulated within primitive meteorites or in solids contaminated by ions from the solar wind, at least some fraction of these elements likely came directly from the gaseous nebula that surrounded the earliest protoplanets.

That last option is especially exciting to present-day planetary scientists interested in constraining Earth’s formation history because it requires some very specific conditions. Since light noble gases like neon don’t dissolve well in seawater, they must have dissolved into a magma ocean — meaning the nebula was still around when Earth was large enough to have a molten surface. That already restricts us to a very specific time in the solar system’s history, but it doesn’t say much about the specific size of the proto-Earth other than “big,” and it doesn’t say much about the state of the nebula other than “it existed.” Recently, Vincent Savignac and Eve Lee (University of California, San Diego; McGill University) successfully refined these constraints to pin down information about both the early Earth and the nebula that surrounded it.

Infant Earths

Savignac and Lee began by growing a grid of infant Earths on their computers via models of gas accretion and atmosphere–magma interactions. Each simulation started with a different proto-Earth mass and nebular density, and each one yielded a different amount of neon in Earth’s deep interior. Excitingly, only a small handful of the scenarios tested ended up with values similar to those observed.

A cartoon of small cores surrounded by gaseous envelopes eventually merging into the Earth.

A schematic of Earth’s formation via embryo formation (when the noble gases enter the mantle) followed by mergers. Click to enlarge. [Savignac & Lee 2026]

On the mass axis, the team found a narrow range of acceptable conditions. If a proto-Earth was less than about 20% of Earth’s present-day mass, it couldn’t accrete much gas. This let it cool rapidly, freezing the magma ocean and shutting down neon dissolution before too much could be trapped inside. On the other hand, if a proto-Earth was more than about 40% of Earth’s present-day mass, it would accrete too much gas, stay molten for too long, and be left with too much neon. On the density axis, the researchers found that when the nebula accreted on to the proto-Earth, it must have been fairly depleted compared to its initial density. This implies that the whole process happened at the end of the nebula’s life, just before it was completely blown away by the proto-Sun.

Savignac and Lee demonstrated that these constraints are robust against the later stages of Earth’s evolution. In its later years, Earth either suffered or benefited from a giant impact, depending on your feelings about the Moon, but the researchers showed that this event doesn’t pose a problem for their models. Overall, this study builds a delightful link between rocks from our deep oceans and the particulars of Earth’s formation, demonstrating the unique power of planetary science to tie together different scientific fields.

Citation

“Constructing the Earth’s Formation History Using Deep Mantle Noble Gas Reservoirs,” Vincent Savignac and Eve J. Lee 2026 Planet Sci. J. 7 135. doi:10.3847/PSJ/ae64f7

J0749+2255

Researchers have detected molecules containing rings and chains of carbon atoms in the vicinity of a rare pair of quasars. The trends in the distribution of these molecules are unexpected, suggesting that more work is needed to understand the conditions surrounding active supermassive black holes.

Infrared Eyes on Molecules in Space

skeletal formulae of aromatic and aliphatic molecules

Examples of aromatic and aliphatic hydrocarbons. Benzene (top left) is the simplest aromatic molecule. Propane (top right) is a simple aliphatic molecule. Propylbenzene (bottom) is an aromatic molecule with an aliphatic chain branching off of it. In these “skeletal” formulae, there is a carbon atom at each vertex, and the remaining atoms (not depicted) are all hydrogens. Single lines indicate single chemical bonds, and double lines indicate double bonds. [Wikipedia; Public Domain]

Across the universe, atoms are combining to form molecules, and our ability to study molecules in distant realms has never been better. JWST is particularly attuned to emissions from molecules engaged in a kind of chemical yoga, stretching their bonds and flexing the angles between their atoms.

JWST’s sensitive infrared eyes have allowed researchers to study the distribution, creation, and destruction of both aromatic (containing one or more rings of carbon atoms in which certain electrons spread out within the ring) and aliphatic (containing chains of carbon atoms) hydrocarbons. These molecules have been spotted in a wide array of environments, and now, astronomers are finding them in more distant and more extreme environments than ever before.

Distant Discovery

SDSS J074922.96+225511.7, or J0749+2255 for short, is a quasar pair seen 3 billion years after the Big Bang. The two feasting supermassive black holes are roughly 12,000 light-years apart, giving researchers a glimpse into the late stages of a galaxy merger and a harsh environment in which to study the survival and destruction of molecules.

Researchers studying J0749+2255 with JWST have previously reported the detection of a 3.3-μm emission feature from aromatic molecules. Now, C. E. Mentzer (University of Missouri), Aigen Li (University of Missouri), and Xuejuan Yang (Xiangtan University) have analyzed JWST spectra of J0749+2255 and found not just widespread aromatic emission at a rest-frame wavelength of 3.3 μm, but also aliphatic emission at 3.4 μm, which they attribute to carbon chains branching off from the aromatic molecules. This likely makes J0749+2255 the most distant galaxy in which both aromatic and aliphatic emission has been detected.

analysis results showing the aliphatic fraction across the quasars and the surrounding region

Aliphatic fractions in the bright central region surrounding the two quasars (top) and in the outer regions (bottom). [Mentzer et al. 2026]

Unexpected Trends

Mentzer, Li, and Yang subdivided the observations into 47 regions and measured the strength of the 3.3- and 3.4-μm features in each region. This analysis found strong aromatic emission nearest the quasars and showed that the fraction of carbon atoms bound up in aliphatic chains is highest close to the quasars.

Both of these findings are unexpected: the harsh radiation environment near the two active black holes is thought to break apart chains of carbon atoms attached to aromatic rings (which should decrease the 3.4-μm emission) and possibly destroy small aromatic molecules (which should decrease the 3.3-μm emission) — yet both of these features are strongest near the quasar cores where the radiation should be most capable of molecular destruction.

The authors speculated that the analysis regions centered on the quasars are large enough that they contain gas that hasn’t been pummeled by the quasars’ intense radiation and outflows, leaving molecules intact and able to produce the observed emission. However, this doesn’t explain the trend of stronger 3.3- and 3.4-μm emission closer to the quasars — necessitating further research into the emitting behavior of aromatic and aliphatic molecules under the extreme conditions of a dual quasar’s neighborhood.

Citation

“Widespread Detection of Aromatic and Aliphatic Emission in the Dual Quasar J0749+2255 at Cosmic Noon,” C. E. Mentzer et al 2026 ApJL 1005 L38. doi:10.3847/2041-8213/ae7e86

Messier 64

The iconic disks of spiral galaxies are well known across the local universe and now far beyond. A recent study looks at the Milky Way to determine when its own disk emerged.

Spinning into Spirals

The Milky Way, a grand spiral galaxy with stars and gas rotating in a disk, did not always look this way. Galaxies begin as chaotic clumps of gas and stars inside a knot of dark matter, and at some point in time, spiral galaxies must transform into the flat rotating disks we observe them as today. Recent JWST observations have uncovered disk galaxies emerging much earlier in the universe than previously thought, shifting our understanding of how quickly spiral galaxies come together and settle into disks. While we cannot study the detailed assembly history of these very distant galaxies, we can dissect galaxies in the local universe to build a better timeline of galaxy evolution.

disk galaxies

JWST images of distant edge-on galaxy disks [NASA, ESA, CSA, STScI, Takafumi Tsukui (ANU)]

Looking as close to home as possible, astronomers have used the kinematics and chemical makeup of stars in our own Milky Way to trace the moment when the galaxy started to host a rotating stellar disk. This period, known as the “spin-up,” marks when the bulk kinematic signature of the galaxy transitioned from one dominated by random motions to one dominated by a rotating disk.

Stars hold on to the kinematic and chemical information they are born with, so stars of different ages and metallicities across the galaxy should trace the development of the disk. Because stellar ages have been difficult to constrain observationally, studies of galactic spin-up have typically relied on readily available metallicity measurements as a proxy for age; however, metallicity is not a clear-cut age indicator, making it difficult to truly distinguish different stellar populations across the Milky Way’s disk. Luckily, new major surveys have recently provided stellar databases adding the stellar age measurements necessary to pin down when the Milky Way spun up.

Dawn of the Galactic Disk

Plots showing stellar age and rotational velocity versus metallicity, [Fe/H].

Plots showing stellar age and rotational velocity (Vϕ) versus metallicity, [Fe/H]. The metallicity range where the age–[Fe/H] relation stalls coincides with the point when the Vϕ–[Fe/H] relation rapidly increases, indicating the age of the spin-up in the Milky Way. Click to enlarge. [Modified from Feltzing et al 2026]

Sofia Feltzing (Lund Observatory) and collaborators used a catalog of over 300,000 subgiant stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope with metallicities, kinematics, and crucial stellar ages to determine when the Milky Way began to host a stellar disk. After making quality cuts to ensure they included only the most robustly measured stars, the authors divided the sample into two distinct stellar populations that settled into the Milky Way’s disk differently: older stars with a high abundance of α elements (like oxygen, magnesium, and silicon) relative to iron and younger stars with low α-element abundances.

With these star samples, Feltzing and team analyzed how both stellar rotational velocity and age varied with metallicity to determine when the Milky Way spun up. They found that high-α stars clearly move from having random motions to being rotationally supported over a short range of metallicities about 12.5 billion years ago, while the low-α stars seem to begin in a rotating disk and stay there. When varying their selection criteria and looking at the full sample, the authors determined that the Milky Way spin-up happened between 12.1 to 12.5 billion years ago — the first time Milky Way spin-up has been age-dated in this way.

These results imply a rapid chemical evolution and change in kinematic properties as stars went from randomly orbiting to rotating in an ordered disk in the Milky Way. The authors suggest that future studies should focus on lower-metallicity stars to better disentangle stars in the disk from stars in the halo, which will lead to a more precise determination of the Milky Way’s spin-up. Upcoming large-scale surveys will make this possible and allow astronomers to build a better picture of galaxy formation in the early universe.

Citation

“Dawn of the Milky Way Disk: Determination of When a Rotationally Supported Disk Appears and Dating the Spin-up of the Disk,” Sofia Feltzing et al 2026 ApJL 1004 L28. doi:10.3847/2041-8213/ae6f14

white dwarf with debris disk

White dwarfs often show signs of metals in their spectra, providing evidence that these evolved stars have accreted planetary material. Could white dwarf spectra also provide evidence for technological activity in these star systems?

A Record of Planets Past

When a Sun-like star reaches the end of its hydrogen-burning lifetime, it first puffs up into a red giant before exposing its white-hot core, which evolves into a white dwarf. This dramatic transition shakes up any planets that happened to be orbiting the star, and some close-in planets may end up crumbling apart, their rubbly remains peppering the surface of the white dwarf.

So far, astronomers have found hundreds of white dwarfs that appear to be polluted with heavy elements from their destroyed planets. These observations provide a valuable look into the bulk compositions of planetary materials outside our solar system. They may also provide a way to detect patterns of chemical abundances that are not natural, resulting from technological processes like industrial refining or the creation of alloys — in other words, a technosignature that is evidence of not just life, but technologically advanced life.

Seeking Signs of Technology

abundances of meteorites compared to white dwarfs

Representation of the chemical abundances of meteorites (pink, orange, and green) and white dwarfs (gray). Most white dwarf abundances overlap with the parameter space defined by the meteorite sample. Click to enlarge. [Huang et al. 2026]

A team led by Bo-Lun Huang (黄博伦) from Beijing Normal University recently investigated whether there is evidence for chemical technosignatures in the current sample of polluted white dwarfs. Huang and collaborators began their investigation with a catalog containing 697 measurements of white dwarfs with metals in their spectra. They applied Bayesian statistical methods to weigh the hypothesis that the chemical makeup of these white dwarfs is entirely natural against the possibility that they contain a blend of natural and technologically altered material.

The team used thousands of chemical abundance measurements from meteorites as a reference for the natural bulk composition of planetary material. For the mixture of natural and processed material, they combined the meteorite reference material with a template that is metal-rich and silicate-poor, with enhanced amounts of iron, nickel, chromium, and manganese.

plot showing evidence for a natural + processed model relative to a natural model as a function of the number of elements detected

Evidence for a model including technologically processed material relative to a purely natural model, as a function of the number of elements detected in the white dwarf. ndet = 0 indicates that only upper limits were obtained on elemental abundances. Higher Bayes factors indicate stronger evidence. The left-hand plot is based on abundances measured from the white dwarfs’ photospheres, while the right-hand plot uses abundances adjusted for diffusion within the white dwarf. Click to enlarge. [Adapted from Huang et al. 2026]

No Strong Evidence, but a Path Forward

Ultimately, Huang’s team found that strong statistical support for the existence of technological processes was uncommon, though there were certain measurements in their sample of white dwarfs that were difficult to reconcile with a solely natural model.

Perhaps unsurprisingly, the team also found that the quality of the chemical abundance measurements affected the constraining power of the observation; some white dwarfs had upper limits for just a few elements, while others had definitive detections of many elements. They found that the most discerning observations recorded iron, magnesium, chromium, and titanium, plus either nickel, silicon, or sodium.

While this work didn’t dredge up firm evidence for technological activity, it provides a jumping-off point for future searches. The handful of white dwarfs in this sample that were fit poorly by a purely natural model could be compared against other technosignature models or targeted with high-resolution spectroscopy. Future measurements of iron and magnesium in polluted white dwarfs may be useful as a preliminary screening tool, helping to pick out intriguing targets for follow-up observations.

Citation

“A Calibrated Bayesian Search for Potential Chemical Technosignatures in Polluted White Dwarfs,” Bo-Lun Huang et al 2026 ApJ 1006 9. doi:10.3847/1538-4357/ae742c

close-up image of the Sun showing a solar flare

Many observations of solar flares suffer from saturation and blooming, causing crucial information to be lost. Researchers recently validated a technique for retrieving information from saturated flare images, unlocking a treasure trove of powerful solar flares for examination.

Solutions for Saturation

Since 2010, the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) has been capturing nearly continuous extreme-ultraviolet images of the Sun’s disk, revealing our star’s dramatic high-energy behavior. Though SDO/AIA’s observations have transformed our understanding of the Sun’s activity, they have limitations: powerful solar flares can saturate the detector, spilling charge into nearby pixels.

This saturation and overflow compromises our ability to study the most energetic solar flares — but the “lost” information may actually be recoverable. When light from an intense flare enters SDO’s instruments, not all of it pools in the saturated region of the detector: some of the light is diffracted by the optics, and by mathematically inverting this pattern of diffracted light, researchers can attempt to extract the encoded information about the saturated region. Researchers have used this technique for more than a decade, but options for validating the results were limited until now.

Solar Orbiter Lends a Hand

Launched almost 10 years to the day after SDO, the Solar Orbiter spacecraft provides an excellent opportunity to test inversion techniques for recovering information from saturated solar images. Solar Orbiter’s Extreme Ultraviolet Imager snaps brief photos of the Sun at a rapid cadence, and its images remain unsaturated even when faced with energetic solar flares.

positions of Solar Dynamics Observatory and Solar Orbiter during a solar flare on 19 March 2024

Positions of SDO (green) and Solar Orbiter (blue) during a solar flare on 19 March 2024. Click to enlarge. [Guastavino et al. 2026]

As described in a recent research article by Sabrina Guastavino (University of Genoa; Italian National Institute for Astrophysics) and collaborators, the ideal setup for testing the inversion technique arose on 19 March 2024, when SDO and Solar Orbiter both viewed a solar flare while separated by just 1 degree in longitude.

Guastavino’s team aligned and reprojected the data, accounting for the slightly different viewing angles of the two spacecraft, then applied an algorithm called Adaptive SE-DESAT to reconstruct the flux within the saturated portion of the SDO image. The team compared the desaturated SDO images to the unsaturated Solar Orbiter images over the course of the flare, finding the same flare morphology and similar time evolution between the two data sets.

sample results of the desaturation process

Example of unprocessed SDO data (top left), desaturated SDO data (top right), Solar Orbiter data (bottom left), and a combination of the two data sources (bottom right). Note that the Solar Orbiter observations have been clipped so that only the highest flare intensities were recorded. Click to enlarge. [Adapted from Guastavino et al. 2026]

A Treasure Trove of Desaturated Data

Overall, these results demonstrate the effectiveness of the inversion technique, though Guastavino and coauthors noted that improvements could be made during the impulsive phase of the flare, when the emission is increasing. The team identified several reasons why the results may not match during this phase, including rapid evolution of the flare during individual exposures.

Despite these areas that require further attention, the validation of this technique unlocks 16 years of solar flare observations from SDO. This especially enhances our sample of powerful solar flares, increasing the available records of the most energetic solar flares by orders of magnitude.

Citation

“Validation of an Extreme-Ultraviolet Desaturation Technique for the Atmospheric Imaging Assembly on Board the Solar Dynamics Observatory Using Observations from the Extreme Ultraviolet Imager on Board Solar Orbiter,” Sabrina Guastavino et al 2026 ApJL 1005 L50. doi:10.3847/2041-8213/ae7d2e

An oblique-angle photograph of a deep crater half in shadow.

NASA is once again sending scientific missions to the Moon. But under the new commercial framework for getting there, researchers need to invent a new method for how to pick where to land.

A New Process for Picking Sites

NASA’s Commercial Lunar Payload Services program is a bold innovation in organizing robotic missions to the Moon. Under this model, rather than keeping the mission process entirely in-house, the agency selects the scientific mission they want to support then simply buys a ride to the lunar surface from a commercial vendor. But, how do you pick a landing site before you know exactly how you’re getting there?

A photograph from orbit of two volcanic mounds on the moon.

The Gruithuisen domes region, the broad area the Lunar-VISE team searched for potential landing sites. Click to enlarge. [Adapted from Williams et al. 2026]

The Lunar Vulkan Imaging and Spectroscopy Explorer (Lunar-VISE) mission, set to launch in mid-2028, was one of the first programs to go through this new landing site selection process. After being officially selected in 2022, the team had just nine months to nail down exactly where their mission should touch down. A recent article led by Jean-Pierre Williams (University of California, Los Angeles) detailed exactly how the team accomplished this task and presented some lessons they learned along the way.

No Parking Lots on the Moon

Picking a landing site is no small task: for context, selecting the landing sites for each of the most recent Mars rovers took five years and multiple community workshops. The Lunar-VISE team therefore took a streamlined and logic-driven approach. They started by explicitly laying out their science objectives: Lunar-VISE’s purpose is to investigate some strangely silicate-rich volcanic formations called the Gruithuisen domes, so they had to land either on or near those. They also had to have access to boulders that were excavated from deep within the domes during a crater formation event, so they had to pick a spot with boulders relatively nearby.

In addition to objectives, they also laid out a slew of constraints. Although they needed boulders nearby, they couldn’t have too many boulders, or any particularly large boulders, since those could pose hazards for landing. There also couldn’t be any steep slopes in the field. Most of the area had to maintain a line of sight with a supporting orbiter for communications, so they couldn’t set down near any ridges. Also, they had to consider how the terrain would cast shadows as the lunar day progressed, since they didn’t want their mission cut short by freezing temperatures and a lack of solar power. As the team quipped, “many interesting, high-science value locations on the Moon may not be in proverbial ‘parking lots.'”

A low-angle photo of a crater and plain on the moon, with arrows and annotations to the landing ellipse, boulders, and the edge of the dome.

An image from the Lunar Reconnaissance Orbiter overlaid onto a terrain model of the final landing site. Click to enlarge. [Williams et al. 2026]

By combing through archival data and working with the team that operates the Lunar Reconnaissance Orbiter Camera, a key asset for making detailed maps of the Moon, the researchers found the perfect spot: alongside a 190-meter-diameter crater named Mareta. This feature is named after Mareta West, one of the first female planetary geologists at the United States Geological Survey and the scientist who selected the landing site for Apollo 11’s historic touchdown.

In addition to presenting their landing site, the researchers offered a handful of lessons to others who may someday be in the fortunate and thrilling position of needing to pick a landing spot on the Moon. For one, they urged teams to coordinate with the Lunar Reconnaissance Orbiter specialists as early as possible, since processing the imaging data for lander-quality maps is a specialized and intensive task. For another, they recommended that all of the software tools used be made publicly available so that future missions don’t need to duplicate their work.

As this article laid out, the Commercial Lunar Payload Services program and Lunar-VISE take us one step closer to making missions to the Moon routine — but we’re still figuring out exactly how to do that.

Citation

“Lunar-VISE Landing Site Selection and Characterization at Mons Gruithuisen Gamma,” Jean-Pierre Williams et al 2026 Planet. Sci. J. 7 161. doi:10.3847/PSJ/ae7d2c

star-forming cloud OMC-2

Do all star-forming regions birth stars with the same distribution of masses? Theory suggests that they do not, but researchers often assume they do for simplicity. Now, ultra-precise observations from Gaia have demonstrated that the initial mass function varies across star clusters in the Milky Way.

A Universal Initial Mass Function?

JWST image of galaxies in the iconic Hubble Ultra Deep Field

The light from distant galaxies is dominated by high-mass stars, requiring the use of the IMF to estimate the stellar mass of a galaxy. [ESA/Webb, NASA & CSA, G. Östlin, P. G. Perez-Gonzalez, J. Melinder, the JADES Collaboration, the MIDIS collaboration, M. Zamani (ESA/Webb); CC BY 4.0]

When a molecular cloud fragments, collapses, and births a star cluster, how many stars form, and what are their masses? The answer to that question is what astronomers term the initial mass function, or IMF: the distribution of masses of stars born in a cluster.

The IMF is important in many areas of astronomy, and it’s relied on especially heavily in studies of distant galaxies. The light from these galaxies is dominated by high-mass stars, with the emission from lower-mass stars lost in the glare, so astronomers must use the IMF to reconstruct the stellar populations of these far-off locales.

Though theory suggests that the IMF should vary with factors like temperature and metallicity, demonstrating these variations has been difficult, even within our own galaxy. Because of this, researchers often adopt a universal IMF drawn from observations of star clusters in the Milky Way. But is the IMF truly universal?

The More the Slope Changes, the More the Break Mass Stays the Same

Determining whether the IMF is universal is more complicated than simply comparing the stars in one cluster to those in another. That’s because what astronomers measure in present-day star clusters is not the initial mass function, but a version of the IMF that has been skewed by millions to billions of years of evolution; over time, high-mass stars die and low-mass stars get ejected, warping the shape of the mass function.

Plots of the stellar mass function

Left: Different break masses arise for different properties (here, the sound speed) of a given star-forming cloud. Right: Evolution of the mass function over time for a single star cluster. Over time, high-mass stars die and low-mass stars are ejected from the cluster, resulting in a decrease in the remaining mass fraction, μ, from 1 to 0.1. The slopes change, but the break mass does not. Click to enlarge. [Adapted from Steinhardt et al. 2026]

However, as demonstrated in a recent research article led by Charles L. Steinhardt (University of Missouri), certain aspects of the IMF may remain unchanged as clusters evolve. When the mass function of a star cluster is described using a broken power law (commonly called a “Kroupa-like” IMF in reference to work by Pavel Kroupa), the slopes of the power-law segments are affected by stellar evolution and dynamical interactions. Crucially, these effects appear not to alter the break mass — the mass at which the IMF transitions from one slope to another. Therefore, differences in the break mass from cluster to cluster reflect differences in the underlying IMF rather than the stellar and dynamical evolution of the clusters.

Insights from Gaia

Thanks to the Gaia spacecraft, which made precise observations of more than 2 billion stars in the Milky Way and beyond, it’s now possible to measure and compare the break masses of individual star clusters. Out of an initial catalog of 7,167 Milky Way clusters observed with Gaia, Steinhardt’s team selected just 110 that were of high enough quality and contained a sufficient number of stars to measure cluster break masses accurately.

Plot of stellar mass function for four Milky Way clusters

Observed mass functions of four Milky Way star clusters. The break masses are clearly different, showing that the IMF must vary from cluster to cluster. Click to enlarge. [Steinhardt et al. 2026]

The team found that the break mass differs considerably between the clusters in their sample, showing that the IMF is not universal. The observed variety of break masses appears to be linked to the age of the cluster, but instead of reflecting the impact of stellar and dynamical evolution — which have no effect on the break mass — these differences reflect the properties of the clouds in which the clusters were born. This implies that the properties of star-forming clouds in the Milky Way have, on average, changed over cosmic time. Thus, a star cluster that formed billions of years ago would have had a different IMF than one forming today.

This finding has implications for studies of high-redshift galaxies, where the properties of star-forming clouds are markedly different from those in the Milky Way. Going forward, Steinhardt and coauthors recommend developing a flexible parameterization of the IMF to capture how this critical function behaves in environments vastly different from our own.

Citation

“Direct Evidence for Stellar Initial Mass Function Variation in the Milky Way,” Charles L. Steinhardt et al 2026 ApJL 1005 L40. doi:10.3847/2041-8213/ae7444

TESS in space

Stellar rotation is a crucial aspect of not only stellar evolution but also exoplanet science, and a recent study has built the largest catalog of stellar rotation periods to date.

Stellar Opportunities with TESS

Since its launch in 2018, the Transiting Exoplanet Survey Satellite (TESS) has scoured the sky, searching for the signature recurring dip in starlight caused by planetary companions. While the primary goal of TESS is to discover exoplanets, the satellite’s mapping of the entire sky has created a rich database of high-quality photometry for millions of stars. These observations offer ample opportunity for scientists to study stellar properties and behavior across the Milky Way.

In particular, stellar rotation is a key property that traces a star’s age, magnetic activity, and internal structure. For exoplanet science, stellar rotation is both a help and a hindrance: it allows us to study how exoplanets may evolve over time with their host stars, but stellar activity can mimic or drown out planet signals, making them harder to detect. A few studies have investigated stellar rotation periods with TESS, looking at specific star clusters and known planet hosts. To date, however, no existing study has produced a larger catalog of TESS rotation periods — a product that would provide a wealth of information for both exoplanet and stellar evolution science.

Creating a Catalog

TESS All-Sky Rotation Survey

Target sample summary showing the TESS sky coverage (top left), histogram of number of TESS observations per star (top right), TESS magnitude as a function of distance to the star (bottom left), and histograms of magnitude, distance, temperature, and color across the sample (bottom right). Click to enlarge. [Boyle et al 2026]

Seeking to build a flux- and distance-limited catalog of TESS rotation periods, Andrew W. Boyle (The University of North Carolina at Chapel Hill) and collaborators used TESS full-frame images to survey the local neighborhood for stellar variability. To measure reliable stellar rotation periods for as large and diverse a sample as possible, the authors made selection cuts in brightness, distance, and data availability to build a target sample of 7,481,412 stars. They generated light curves for each observation of each star and searched them for periodicity, or repeated variation in brightness.

Not all brightness variations present in a star’s light curve are due to stellar variability — instrumental systematics and artifacts from the spacecraft’s orbital period can produce periodic variability. To combat this, the authors created a classification algorithm to select sources whose periodicity is most likely due to true stellar variability rather than instrumental or observational effects. Pairing this classification with some additional validation criteria, the authors built the TESS All-Sky Rotation Survey (TARS), a catalog of periods for 1,046,317 stars within about 1,600 light-years of our Sun.

Map of fast rotators in TARS sample

Map of all TARS stars within about 1,600 light-years of the Sun (left) and only the fast-rotating stars in the survey, highlighting clustered populations (right). Click to enlarge. [Boyle et al 2026]

Implications of TARS

Looking more finely at the TARS catalog, the authors provided additional quality cuts to remove other potential sources of stellar variability like binary companions or pulsations. The authors estimated that roughly 93% of their measured periods are due to stellar rotation, which expands the number of stars with known rotation periods by a factor of 2.3 within about 325 light-years and by a factor of 4.0 within about 1,600 light-years. As the largest homogeneous catalog of stellar rotation periods to date, TARS lays the groundwork for studies of stellar evolution, exoplanet discovery and evolution, and even Milky Way structure. For example, the authors found that when mapping the fast-rotating, typically younger stars in TARS, the location of young stellar associations in the local neighborhood became significantly clearer. This underscores the importance of this catalog for a range of science goals, and future work will only improve upon the data provided by TARS.

Citation

“The TESS All-Sky Rotation Survey: Periods for 1,046,317 Stars within 500 pc,” Andrew W. Boyle et al 2026 ApJS 284 75. doi:10.3847/1538-4365/ae6657

little red dots seen with JWST

One of the biggest discoveries from JWST’s tenure is a population of compact reddish objects nicknamed “little red dots.” Numerous theories have been proposed to explain the small sizes, high luminosities, and characteristic “V”-shaped spectra of these objects, and today we’ll examine two recent research articles that have explored the identity of the universe’s most mysterious inhabitants.

Red Dot, Blue Dot

You can tell a lot about a person by looking at their friends — and the same might be true for little red dots. A team led by Josephine Baggen (Yale University) examined a sample of 83 little red dots imaged with JWST. They found that 43% of the little red dots in this sample had a little blue companion: an ultraviolet-bright object within a projected separation of 1,630–16,300 light-years. The brightest little red dots were even more likely to have a blue companion; 80% of the brightest objects in the sample were paired up.

Baggen’s team set out to test the hypothesis that these red–blue pairs are fundamentally linked rather than coincidental. Under this hypothesis, the ultraviolet-bright blue companions were assembled first. The ultraviolet radiation from these objects suppressed the cooling of molecular hydrogen in pristine gas clouds in the early universe, causing the gas to skip the usual star-forming process and instead form a massive compact object such as a black hole star, supermassive star, or quasi-star — which we see as a little red dot.

plot of Lyman-Werner radiation versus projected separation

The companion’s mean flux density from 91.2 to 111 nm versus projected separation between the blue companion and the little red dot. The red dashed line shows the estimated values necessary for gas clouds to collapse. Click to enlarge. [Baggen et al. 2026]

Baggen and coauthors investigated whether the ultraviolet radiation from the blue companions is strong enough to have triggered this transformation. The team used spectral energy distribution modeling to determine the luminosities of the blue companions from 91.2 to 111 nanometers. This analysis showed that the radiation from the blue companions is equal to or greater than the threshold necessary to encourage the direct collapse of a gas cloud into a massive compact object.

If little red dots form thanks to their little blue companions, that would imply that every little red dot has or had such a companion. Though little blue companions weren’t so universal in the sample used in this work, the team noted that their analysis techniques, combined with observational limitations and other factors, likely yielded a smaller number of blue companions than are actually present. Further simulations exploring the collapse of pristine gas clouds into massive compact objects and high-resolution spectroscopic observations of little red dots can illuminate the potential link between these objects.

globular cluster NGC 1851

The densely packed globular cluster NGC 1851, as seen by the Hubble Space Telescope. [NASA, ESA, and G. Piotto (Università degli Studi di Padova); Processing: Gladys Kober (NASA/Catholic University of America)]

Little Red Dots as Young Globular Clusters

John Chisholm (The University of Texas at Austin) and collaborators hypothesized that little red dots represent a brief phase in the formation of globular clusters. In this hypothesis, the rest-frame ultraviolet emission of little red dots comes from the hot young stars of the newborn cluster, while the rest-frame optical emission comes from a single supermassive star at the cluster’s heart. Thus, in this framework, the little red dot phase lasts only as long as the fleeting lifespan of the supermassive star.

Chisholm’s team first showed that the spectrum of a young globular cluster with a supermassive star at its center is similar to the observed spectrum of a little red dot. But showing that the emission properties of globular clusters in formation and little red dots are similar is not enough — it’s also necessary to investigate whether the numbers and masses of these objects line up.

mass functions of little red dots and globular clusters

Comparison of the mass functions of little red dots evolved forward to the present day (blue line) and globular clusters in the Milky Way and Virgo (blue symbols). The results for both populations have been normalized to emphasize the shape of the distributions. Click to enlarge. [Chisholm et al. 2026]

To do this, the team propagated the observed mass function of little red dots at a redshift of z = 7 forward in time to z = 0. This process accounted for the rapid evolution of the supermassive star into a black hole, as well as the evolution of and feedback from the massive stars in the cluster. Comparing the resulting mass function to the population of present-day globular clusters, the team found that the mass functions had very similar shapes, and the number densities of little red dots and globular clusters in the present day are estimated to be of the same order of magnitude: 0.1–0.3 Mpc-3 and 0.8 Mpc-3, respectively.

In addition to describing how the properties of globular clusters in formation match those of little red dots, Chisholm’s team outlined some testable predictions for this scenario, including formation timescales and chemical abundance patterns. If this hypothesis withstands further scrutiny, little red dots may provide a valuable look at the early years of some of our universe’s oldest star clusters.

Citation

“Connecting the Dots: UV-Bright Companions of Little Red Dots as Lyman–Werner Sources Enabling Direct-Collapse Black Hole Formation,” Josephine F. W. Baggen et al 2026 ApJL 1002 L4. doi:10.3847/2041-8213/ae58a5

“Little Red Dots as Globular Clusters in Formation,” John Chisholm et al 2026 ApJL 1004 L4. doi:10.3847/2041-8213/ae6dae

A rendering of a Jupiter-like planet floating in front of a galaxy.

Microlensing surveys have discovered plenty of regular exoplanets, but more surprisingly, they’ve also turned up many solo Neptunes with no star nearby. New research suggests that first impressions might be deceiving, however, and that at least some of these planets might not be so alone: they just have a complicated family history.

An Abundance of Exo-Neptunes

There are simply too many Neptune-like exoplanets in our galaxy. Or at least that’s the current feeling astronomers get from gravitational microlensing surveys, which look for exoplanets during short-lived magnification events caused by chance alignments between stars. These surveys have now found about a dozen so-called “free-floating” planets, and while this doesn’t sound like that many, running the numbers reveals that this tiny sample implies that there are about two free-floating Neptune-size planets for every star in the galaxy.

A schematic graph of a large pulse and a smaller narrower pulse superimposed on top.

An illustration of how exoplanets are found via microlensing. The broad first bump is caused by the host star magnifying the light from a background star; the narrow second bump is caused by the planet acting as a lens as well. “Free-floating” planets create only one bump. [Adapted from NASA, ESA, and A. Feild (STScI)]

The idea that there are more free-ranging Neptunes than stars is unsettling, and astronomers aren’t yet sure how this many planets ended up so isolated. It’s possible that these objects simply formed disconnected from any planetary system, but it’s unclear how something so small could collapse from the interstellar clouds that usually produce stellar-mass objects. It’s also possible that the planets formed around stars in the usual way, only to be later kicked out by some violent dynamical process — but this would either require too much time or too many giant planets capable of ejecting the lower-mass ones.

However, new research by Sam Hadden (Canadian Institute for Theoretical Astrophysics) and Yanqin Wu (University of Toronto) presents an alternative idea: what if at least some of these free-floating planets aren’t fully on their own, but instead remain estranged but weakly bound to their parent stars?

Simulated Scattering

Two celestial objects need to align nearly perfectly in order to create a microlensing pulse that we can detect. For an exoplanet orbiting a star, we should observe two of these pulses: one when the host star drifts in and out of alignment with a background star, and one when the nearby bound planet does the same. In the case of a free-floating planet, there’s only one pulse, and we therefore assume that there is no host star. Hadden and Wu noticed that since the alignment has to be so precise for microlensing to occur, it’s possible that a seemingly free-floating planet is simply widely separated from its host star, and the star managed to dodge the magnification effect. In other words, these planets might not be free floating at all, just on wide and eccentric orbits.

A two-panel plot showing how the semimajor axis and inclination of 5 planets evolve over time.

The orbital evolution of a five-planet system that undergoes planet–planet scattering. Each line represents one planet; note that in the end two are ejected, two end up on wide detached orbits, and the fifth ends up on a tightly bound inner orbit. Click to enlarge. [Hadden & Yu 2026]

The researchers decided to test whether it’s possible to create these kinds of orbits via a known dynamical process called planet–planet scattering. As the name implies, during this process, planets that begin on orderly orbits around their parent star undergo a dramatic rearrangement as they jostle each other around through gravitational interactions. The researchers created two types of simulations: one with a collection of equal-mass planets, and another in which one planet dominates over a brood of smaller ones. After setting up the systems, they let the “dynamical havoc” proceed for a few hundred million years, then surveyed the aftermath.

They found that both types of simulations readily created the “detached” objects needed to mimic free-floating planets. In fact, the most common outcome was for two or three planets to be bullied into far-out orbits by a planet that then plunges onto a tight inner orbit extremely close to the star.

Though the authors caution that this process likely doesn’t explain all of the free-floating planets observed to date, this is an exciting model that would dramatically lower our estimates of the number of Neptunes roaming alone between the stars.

Citation

“Free Floating or Merely Detached?,” Sam Hadden and Yanqin Wu 2026 ApJ 1000 70. doi:10.3847/1538-4357/ae6508

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