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The two brightest objects a wide-field optical survey can pick out at the cosmic dawn are not always what they appear to be. In a paper posted on 18 August 2026, a team led by Daming Yang of Leiden University reports that two sources originally classified as faint quasars in the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) catalogue are instead extremely UV-luminous galaxies, and that the only stellar populations able to reproduce their spectra contain stars heavier than about 225 solar masses each Yang et al. 2026 preprint on arXiv. The finding lands in a regime where galaxy and quasar brightness functions overlap, and the result means that source classifications, and the inferred demographics of both galaxies and quasars in this crossover regime, need revisiting.

The confusion zone sits at the extreme bright end of the ultraviolet galaxy luminosity function during the epoch of reionisation. Galaxies and quasars both produce blue ultraviolet continuum, and at absolute magnitudes around M_UV ≈ -23.5, the faintest quasars and the brightest starbursts are visually similar in a ground-based photometric catalogue. SHELLQs, a long-running campaign using the 8.2-metre Subaru telescope and the Hyper Suprime-Cam wide-field imager, has spent a decade picking out candidate high-redshift quasars from the Subaru Strategic Program imaging and confirming them spectroscopically Matsuoka et al. 2020 SHELLQs IX paper. Its sixteenth data release added 69 confirmed quasars at redshifts between 5.8 and 7.0 Matsuoka et al. 2021 SHELLQs XVI paper. Two sources in that wider sample, J1450-0144 at redshift 6.627 and J1429-0104 at redshift 6.796, looked like faint quasars in the discovery spectra from GTC/OSIRIS and Subaru/FOCAS, and they were catalogued as such.

JWST changed the picture. Yang and colleagues obtained near-infrared spectroscopy with NIRSpec using the G140H and G235H gratings, which together cover rest-frame wavelengths from about 1200 to 4000 angstroms in these high-redshift targets. The new spectra reveal three spectral signatures that the original discovery spectra could not resolve: narrow nebular emission lines including the [O II] doublet at 3727/3730 angstroms and [Ne III] at 3870/3969 angstroms, which are produced by interstellar gas ionised by hot stars rather than by an accreting black hole; broad He II 1640 emission with rest-frame equivalent widths of 8.8 plus or minus 1.2 angstroms in J1450 and 3.7 plus or minus 1.1 angstroms in J1429, a feature too strong for any AGN-powered continuum at this redshift; and prominent P Cygni profiles in the high-ionisation resonance lines N V 1240, Si IV 1400, and C IV 1550, the spectroscopic fingerprints of fast stellar winds driven by the hottest, most luminous stars.

The follow-up ALMA Band-6 observations add the second piece of evidence. ALMA detected luminous [C II] 158 micrometre emission in both systems, with line luminosities of about 0.8 times 10 to the 9 solar luminosities for J1450 and 4.1 times 10 to the 9 solar luminosities for J1429. J1429 additionally shows bright dust continuum, and the [C II] and dust peaks are offset by about 5.4 kiloparsecs from the rest-frame UV emission seen by NIRSpec and Subaru/HSC. The offset is a structural clue: it shows that J1429 is not a single point-like accretion disk masquerading as a galaxy, but a spatially resolved system with cold gas and dust that have decoupled from the hot stellar light, which is exactly the geometry of an extreme starburst rather than a quasar.

The interpretation hinges on a population-synthesis fit. The authors tested two classes of models against the new spectra. The first, BPASS (Binary Population and Spectral Synthesis) with standard upper-mass cutoffs around 100 solar masses, fails to simultaneously reproduce the broad He II 1640 emission and the strong wind profiles in N V, Si IV, and C IV. The second class, BPASS extended with a dedicated prescription for very massive stars above 100 solar masses, succeeds. Under the VMS models, the equivalent-width diagnostics imply an upper-mass cutoff above 225 solar masses for J1429, while J1450 lies beyond even the 475-solar-mass endpoint of the model grid. The star-formation durations are short: 2 to 4 million years for J1450, with a broader allowed range for J1429. Stellar masses come out at log(M_star/M_sun) between about 9.2 and 9.9, with star-formation rates of roughly 300 to 540 solar masses per year.

The reference spectrum in the model grid comes from R136, the central cluster of the Tarantula Nebula in the Large Magellanic Cloud Crowther et al. 2016 R136 massive-star census. HST/STIS spectroscopy of R136 has established that the cluster hosts individual stars well above the 150-solar-mass conventional upper limit. When the team plots the JWST/NIRSpec spectra of J1450 and J1429 against the stacked spectrum of the seven most massive stars in R136, initial masses between about 100 and 300 solar masses, the wind profiles and He II emission match almost feature for feature. The reionisation-era galaxies look, at high-ionisation wavelengths, like a cosmological-scale version of a local starburst cluster.

The result has direct implications for the demographics of the early Universe. Bright-end UV luminosity function measurements during reionisation have historically assumed that anything more luminous than a threshold around M_UV = -23 is dominated by quasars; the faintest “quasar” bin is then used to constrain the AGN duty cycle at early times. If a non-trivial fraction of that bin is instead powered by VMS-driven starburst galaxies, the inferred quasar space density drops, the inferred galaxy space density rises, and the contribution of early galaxies to reionising the intergalactic medium grows. The paper notes explicitly that the inferred demographics of both galaxies and quasars in the crossover regime need revisiting.

The story is also a methodological lesson in spectroscopic re-classification. SHELLQs selected these sources on the basis of photometric dropout signatures and broad-line spectral markers visible at low signal-to-noise in 8-metre-class spectra. JWST/NIRSpec at higher resolution and sensitivity shows that the broad lines were real stellar wind profiles, not the broad permitted lines of an accretion disk, and that the narrow nebular lines, which were below the discovery spectra’s noise floor, are decisive for reclassifying the sources as galaxies rather than quasars. Crossover-regime classification at cosmic dawn is now an empirical problem rather than a photometric one, and ALMA’s structural imaging (the 5.4-kpc UV/[C II] offset in J1429) provides the second confirming axis.

The paper is a preprint, resubmitted to Nature Astronomy on 20 July 2026 according to the arXiv metadata, so the model grids and equivalent-width fits will be re-examined through peer review. The next observational test is straightforward: more JWST/NIRSpec spectra of SHELLQs candidates in this brightness range, paired with ALMA [C II] imaging to look for the same offset geometry. If even a third of the M_UV around -23.5 bin turns out to be VMS-driven starbursts rather than faint quasars, the early-Universe census shifts noticeably, and R136 stops being a peculiar local object and starts being a representative sample of how the first massive stellar populations lit up their galaxies.

Astronomers using the Atacama Large Millimeter/submillimeter Array have resolved the surface of Betelgeuse closely enough to see two hot patches on its outer shell, one of them about 800 kelvin warmer than the surrounding gas, and the brighter one has not moved in seven years. That kind of stability matters because the standard picture of a red supergiant is a churning ball of plasma whose outer layers roil with bubbles rising and falling on timescales of months to a few years. A feature that survives for at least seven years without drifting or fading is a different class of object than a single convective plume, and the new ALMA images are forcing stellar physicists to redraw how a supergiant’s surface organizes itself.

The observations were taken in August 2023 using ALMA’s longest-baseline configuration, which gave the team angular resolution down to about 7 milliarcseconds at the shortest wavelengths. That is sharp enough to resolve structure at roughly 1.1 to 1.3 stellar radii, the inner part of the photosphere where most of the millimeter-wave light originates. Compared against a comparable 2015 dataset, the new view shows that Betelgeuse is not just irregular but persistently irregular, with a stable geometry that convection models have to reproduce.

Betelgeuse is the closest red supergiant to Earth that is bright enough to be imaged in this detail, and it is the prototype for an entire class of massive evolved stars that seed the interstellar medium with heavy elements when they explode. Anything we learn about how its surface is structured carries over to every other red supergiant we can see in nearby galaxies, and to how those stars shed mass in the centuries before they go supernova.

Until recently, the main puzzles about Betelgeuse were its brightness, which had an unexplained dip in late 2019 and early 2020, and the possibility that it might be hiding a smaller companion star, which a separate VLT team reported in July 2026. Surface structure is a third puzzle, and arguably the more physically interesting one, because the photospheric pattern tells you how mass is being transported from the deep interior out into space. If convection organizes itself into stable polar plumes, the mass-loss geometry of the entire star follows from that pattern. The new ALMA data show the NE hot patch sitting near one of the proposed rotation poles, which suggests convection may be funneled along the polar axis rather than scattered randomly across the surface.

For stellar physics, this is the first time anyone has tracked a hot patch on a red supergiant for as long as seven years and shown that it does not rotate with the surface the way sunspots do. That is a measurable signal that large-scale convection in these stars is anchored to something deeper than the photosphere, and the natural candidate is the rotation axis itself.

The new paper, ALMA high resolution observations of Betelgeuse: Persistent structure spanning the inner atmosphere by Bill Dent and colleagues at ESO and several partner institutions, was posted to arXiv on 19 August 2026 and accepted for publication in Astronomy & Astrophysics. The team’s lead author, Bill Dent, is an ESO astronomer who has worked on ALMA instrumentation since its commissioning era, and the paper combines a fresh long-baseline dataset with archival 2015 observations taken at the same wavelength and similar resolution.

Both datasets image Betelgeuse in millimeter-wave continuum light, where the emission comes from an optically thick shell of gas at the star’s effective surface. The 2023 run reached a synthesized beamwidth down to about 7 milliarcseconds at 0.6 millimeters and observed multiple molecular lines, including silicon monoxide and carbon monoxide isotopologues, that trace gas out to about 2.5 stellar radii. By comparing the two epochs, the team could measure how stable each feature was on a seven-year baseline, something earlier work could not do because no comparable 2015 image existed at this resolution.

The headline result is that the brightest hot patch, located to the northeast of the star’s center, is essentially unchanged in both position and intensity across the seven-year gap. A second, cooler patch to the southwest has held its position too, although its intensity is closer to the surrounding photosphere and harder to distinguish in single-epoch images. Beyond these hot regions, the team found radial corrugations in the apparent stellar radius of up to plus-or-minus 6%, concentrated in one sector, indicating that the star’s surface ripples gently rather than ballooning out uniformly. None of these features show the kind of rotation signature that a sunspot would, which is the part that surprised the team.

The physics underneath these images is the same convection problem that has occupied red-supergiant theorists for decades, and the new data let the team test specific models rather than argue from a single snapshot. In a typical convection simulation for a star of Betelgeuse’s mass and luminosity, the largest convective cells span roughly a third of the stellar radius and have lifetimes of months to a few years. A patch that survives for seven years is longer-lived than the deepest such cell in current simulations, which is one of the reasons the team is careful to call the features “persistent” rather than “stationary.”

The millimeter continuum emission that ALMA detects is sensitive to gas temperature near 2300K in Betelgeuse’s atmosphere. That is cooler than the visible photosphere at around 3600K, but it sits in a region where the gas is still optically thick, so the millimeter image effectively maps a shell slightly above the visible surface. The 800K enhancement in the NE hot spot, on top of a 2300K baseline, corresponds to a roughly 35% increase in local gas temperature, which is well outside the noise floor of the new observations and consistent between 2015 and 2023.

The second surprise is the orientation. Earlier interferometric work, including VLTI observations at infrared wavelengths, had constrained Betelgeuse’s rotation axis to lie roughly along a particular line on the sky. The NE hot patch sits close to one of the proposed poles, which suggests that polar convection in a rapidly rotating massive star may be more stable than equatorial convection. This idea has been around in theoretical work, but the new ALMA images are the first clean observational handle on it.

For the engineering side, the result is also a vindication of ALMA’s long-baseline capability. The longest baselines, stretching across the Chajnantor plateau at up to 16 kilometers, are what give ALMA its 7-milliarcsecond beam at submillimeter wavelengths. Most ALMA science is done at more compact configurations, where the resolution is much coarser and a feature like the NE hot patch would simply smear out. The team used the most extended configuration specifically to resolve structure at one to two stellar radii, and the fact that the same configuration was used in 2015 and 2023 is what makes the seven-year stability comparison possible.

The clearest single fact to take away from this paper is that Betelgeuse’s photosphere is not a uniform, churning surface: it has structure that has held its position for at least seven years, and the most prominent feature sits about 800K hotter than its surroundings. That is enough to update the textbook picture of a red supergiant from “uneven and roiling” to “uneven, roiling on short timescales, but with a small number of long-lived anchored features near the rotation poles.”

What comes next is a finer-grained temporal sampling. The 2015 and 2023 epochs bracket a seven-year gap that is much longer than the expected convective turnover time, so the team cannot yet say whether the hot patches are perfectly stable or drifting slowly. A second long-baseline observation in 2027 or 2028 would catch the star near the next seasonal alignment and tighten the upper bound on drift to a fraction of a stellar radius. That would let the team test whether polar convection in Betelgeuse is locked to the rotation axis over decades, or whether the patches are simply long-lived plumes whose anchoring is statistical rather than rigid.

The wider significance for stellar astrophysics is that millimeter-wave interferometry has now joined optical and infrared interferometry as a tool for resolving supergiant surfaces, and the combination is starting to produce constraints on the deep interior that no single technique could supply alone.

On June 16, 2023, a single light pulse appeared inside a vat of liquid xenon buried 1,480 meters below the Black Hills of South Dakota. Most flashes like it are noise: stray gamma rays, the occasional neutron, the radioactive decay of trace contaminants in the detector’s titanium walls. This one, recorded in the LUX-ZEPLIN detector at the Sanford Underground Research Facility, did not fit those explanations. By the time the collaboration finished analyzing the data and presented it at the TeV Particle Astrophysics conference in Japan on September 1, the event had become the most credible WIMP dark matter candidate any direct-detection experiment has recorded in a decade (Berkeley Lab, 1 September 2026).

That framing, for the careful reader, does the work. “Most credible” is not “discovery.” The single event sits at 2.6 sigma, where 5 sigma is the threshold physicists treat as a confirmed observation. The probability that background processes alone could produce such a flash is roughly one in two hundred, tantalizing, but not the kind of number on which you write a Nobel citation. The collaboration knows this. Rick Gaitskell, the Brown University physicist who serves as LZ’s spokesperson, called the event “something interesting” and made clear that more data is the only path to certainty (Berkeley Lab, 1 September 2026).

What makes the signal worth talking about is the experiment itself, and what it takes to eliminate every other explanation. The LZ detector holds ten tonnes of liquid xenon kept near 178 kelvin inside a titanium cryostat, nested inside an outer cryostat, surrounded by 17,000 gallons of water in a tank the size of a small swimming pool, wrapped in gadolinium-loaded liquid scintillator, and lodged beneath a mile of Homestake Mine rock (LUX-ZEPLIN Collaboration, NIM A 2020). A WIMP, if WIMPs exist, would interact with the xenon nucleus perhaps once per tonne per year. Everything else has to be ruled out, photon by photon, neutron by neutron.

The story of how dark matter became a question starts almost a century ago. In 1933, Fritz Zwicky applied the virial theorem to the Coma Cluster and concluded that the visible galaxies could not possibly account for the cluster’s rotational behavior; he called the missing mass “dunkle Materie” (Zwicky, Helvetica Physica Acta 1933). Forty years later, Vera Rubin’s spectra of the Andromeda galaxy showed stars in the outer disk moving at the same speeds as those near the center, the rotation curves that have since been measured for thousands of spiral galaxies and remain the cleanest gravitational evidence for unseen mass (Rubin & Ford, ApJ 1970). In 2006, observations of the Bullet Cluster sharpened the argument: during the collision of two galaxy clusters, the X-ray emitting gas decelerated while the gravitational lensing signal passed straight through, implying that most of the mass is in some non-luminous, non-baryonic form (Clowe et al., ApJ 2006).

If dark matter is real, it must be made of something. The leading family of candidates for forty years has been WIMPs, weakly interacting massive particles with masses in the GeV-to-TeV range, predicted independently by supersymmetry and by simple thermal-relic calculations. The relic density is Ω_chi * h² ≈ 0.1, and a coupling near the weak scale gives roughly the right answer, the so-called “WIMP miracle.” None of the direct-detection experiments built to test this prediction has produced a confirmed signal (LZ Collaboration, PRL 2023). Until June 16, 2023.

The LZ detector works because xenon has two properties that are nearly ideal for this kind of search. Its nucleus is heavy, atomic mass 131 on average across xenon’s nine stable isotopes, so a WIMP recoiling off it transfers more momentum than it would off a lighter target. When a particle scatters in liquid xenon, the interaction produces two distinct signals the experiment can read separately: a prompt flash of scintillation light called S1 and a delayed pulse of electrons liberated by the ionization, drifted upward through the liquid into a gas layer where they produce electroluminescence, called S2.

The ratio of S2 to S1 is the discriminator. Electromagnetic interactions, the gammas, betas, and Compton scatters that constitute the bulk of background, produce dense ionization tracks with relatively modest S1, yielding a low S2/S1 ratio. A nuclear recoil, the kind a WIMP would produce if it kicked a xenon nucleus, generates denser ionization per unit of scintillation and a much higher ratio. Plotting S1 against log(S2/S1) and overlaying the two populations gives two well-separated bands. Anything that lands above the electron-recoil band and inside the nuclear-recoil region is, by construction, a candidate.

To get the bands that clean, LZ has to throw out most of its own data. The xenon sits in a titanium time projection chamber about 1.5 meters in diameter and height, with seven tonnes of active liquid in the central volume and roughly 5.6 tonnes kept as the inner fiducial mass. Only events in the fiducial volume are kept; events near the walls are rejected because the dense walls themselves are the largest source of external gamma radiation (LZ Collaboration, NIM A 2020). The chamber is watched by 494 three-inch photomultiplier tubes arranged top and bottom, reconstructing event position to within millimeters. The water tank outside the cryostat is instrumented with 120 PMTs that flag any cosmic-ray muon that might have made it through the rock; the gadolinium-loaded scintillator absorbs neutrons, the most dangerous background because they produce exactly the same S2/S1 signature as a WIMP. The collaboration estimates that the detector now sees about one event per year in the search region from known backgrounds, and on June 16, 2023, it saw exactly one.

The new analysis, led by Sam Eriksen of the University of Bristol, looked at 220 live days of data collected between March 2023 and April 2024, but went further than previous LZ searches. Where earlier analyses looked for the simplest spin-independent WIMP-nucleus coupling, Eriksen’s group widened the energy window to catch interactions that deposit more energy in the detector. The single event was in that high-energy tail (Berkeley Lab, 1 September 2026).

What does the signal imply, if it is real? The collaboration’s best fit suggests a WIMP with mass at least 200 GeV/c², heavier than 200 protons, and a coupling to ordinary matter that is not the simplest spin-independent contact interaction but something more structured. The team has not yet published a cross-section limit curve; that comes when the paper appears on arXiv and is submitted to Physical Review Letters.

The next move is statistical. LZ is still running at SURF and continues to accumulate data; a second event at similar energy would push the significance up sharply, while a long absence would let the signal fade. The competition is also still running. XENONnT at Gran Sasso in Italy uses a similar liquid xenon TPC; PandaX-4T at the China Jinping Underground Laboratory uses four tonnes; both have published null results as of 2025 but are taking more data. The global direct-detection community will, over the next two years, accumulate enough xenon-years to test the same mass range LZ has begun to probe. If the June event was a WIMP, one of the others will see one too.

Two thousand and twenty-six has already been a year for hints. Dark matter remains the largest single thing we cannot name. LZ has spent four years underground doing the slow patient work of elimination. It has built a machine that produces, on average, one spurious-looking event per year. It recorded one.

A NASA SmallSat called Pandora finished its commissioning campaign in mid-August and started routine science observations this week, becoming the first spacecraft ever launched under NASA’s Astrophysics Pioneers program to begin returning data. The mission’s job is unglamorous and foundational: stare at known transiting exoplanets for 24 hours at a time, in visible and near-infrared light together, and work out how much of the signal that astronomers have been calling “the planet’s atmosphere” is actually the star’s surface talking back. Over its year-long primary mission, Pandora will repeat that pattern at least 10 times each on at least 20 different worlds (NASA Science, Aug 25, 2026).

Pandora is not a flagship-class observatory. It is a 45-centimeter telescope in a small-satellite bus, launched on January 11, 2026, with a cost cap closer to a university instrument than to a NASA great observatory. The trade is that the mission gives up raw sensitivity and trades it for time: it can spend full days on a single target, something James Webb Space Telescope, Hubble, or any of the other big telescopes simply cannot afford to do, because their schedules are filled with hundreds of competing requests (NASA Science mission page).

Transit spectroscopy is the dominant way the field measures exoplanet atmospheres today. When a planet crosses in front of its star, a thin sliver of starlight passes through the planet’s atmosphere on its way to Earth, and the wavelength-by-wavelength absorption of that light is supposed to encode the composition of the atmosphere. Water, methane, carbon dioxide, hazes and clouds all leave fingerprints at characteristic wavelengths, and a community of thousands of papers since 2002 has built up an enormous catalog of “detected” molecules on this premise.

The premise has a quiet problem. Stars are not uniform disks. Their surfaces host hotter, brighter patches called faculae and cooler, darker patches analogous to sunspots, and those patches grow, shrink, and rotate across the star’s face on timescales of hours to weeks. When the planet transits, the starlight that grazes the planet’s atmosphere is the light coming from the exact patch of the star covered by the planet at that moment. If that patch happens to be a facula, the recorded spectrum is biased bright; if it is a starspot, the spectrum is biased dark. Both biases can mimic or erase molecular features that the atmosphere alone would have produced.

This contamination problem has been written about for years, most concretely in a 2018 paper by Benjamin Rackham (then at Harvard, now at MIT) and Daniel Apai, which showed that starspot and facula crossings could fake the entire water feature in an Earth-sized planet’s transit spectrum, with the implication that several claimed habitable-zone water detections needed re-evaluation (NASA Science, Aug 25, 2026). Rackham is now on the Pandora team. The mission is, in a real sense, a purpose-built response to the contamination question his paper raised. That response has implications for how the next decade of Webb and Ariel spectra should be interpreted.

Pandora is the first mission under NASA’s Astrophysics Pioneers program, a line that NASA created in 2020 to fund astrophysics SmallSats at roughly $20 million each, with a higher-than-usual tolerance for risk. Pioneers missions are meant to answer focused scientific questions with focused instruments, on short timelines and modest budgets, and to give early-career principal investigators a path to flying a mission. Pandora was selected in the inaugural 2021 call (NASA Science mission page).

The principal investigator is Elisa Quintana at NASA’s Goddard Space Flight Center, with project management and engineering at Lawrence Livermore National Laboratory. The telescope itself was a joint development between Livermore and Corning Incorporated: an all-aluminum 18-inch (45 cm) primary, chosen for its thermal stability over a long stare. The detectors are the heart of the instrument, and the near-infrared one is a Teledyne HxRG part originally built and qualified as a flight spare for the James Webb Space Telescope (NASA Science, Aug 25, 2026). The bus was built by Blue Canyon Technologies, which also handled spacecraft assembly, integration, and environmental testing, and which provides ongoing mission operations support. The University of Arizona leads mission operations, and NASA’s Ames Research Center performs the data processing.

Pandora launched on January 11, 2026, into low Earth orbit. The commissioning campaign that followed took roughly seven months, longer than the four-to-six months NASA’s SmallSat missions often need, mostly because of the precision pointing required to hold the telescope on a star and not drift during a 24-hour exposure. By mid-August, deputy project manager Jordan Karburn of Lawrence Livermore was ready to call it: the spacecraft is healthy and all the instruments are performing as well as the team had hoped. Routine science observations began on August 25, 2026 (NASA Science, Aug 25, 2026).

The instrument’s central trick is the simultaneous visible and near-infrared stare. When Pandora points at a star that is hosting a transit, both detectors record photons at the same time. The visible detector measures the brightness of the star across the stellar surface, including the changing pattern of spots and faculae as the star rotates. The near-infrared detector measures the transit spectrum itself, where the planet’s atmospheric absorption lives.

To turn those two measurements into a contamination-free planet spectrum, the team uses the pattern of brightening and dimming in the visible band to model what the star was doing during the transit in the infrared. They subtract the inferred stellar component from the observed infrared spectrum, leaving the planet’s absorption as the residual. That is the same general technique the field has applied to individual Hubble and Spitzer observations, but applied across a whole program at a depth and time coverage those missions could never match.

The visible detector alone does not give you a clean stellar surface map, because the planet is also blocking part of the star during the transit. Pandora solves that by spending 24 hours on each target, with the transit landing somewhere inside that window. The 20 hours outside the transit capture the stellar rotation signature cleanly, and the 4-hour transit window captures the planet’s absorption while the stellar pattern is still being monitored in the visible.

The 20-target, 10-observation, 24-hour-stare program is calibrated against a smaller list of well-characterized exoplanet host stars that other observatories have already studied in detail. The plan is that Pandora will first nail down the stellar contamination correction on those targets, where independent Webb and Hubble spectra exist for cross-checking, and then apply the validated correction to more challenging targets further out.

The Pandora team’s claim, made by project scientist Knicole Colón at NASA Goddard, is that combining Pandora’s many-hour stares with shorter Webb snapshots will give the community the first set of planet spectra that are demonstrably free of the starspot/facula confusion that has plagued the field. That is a specific, testable claim, and the year-long primary mission is sized to deliver it (NASA Science, Aug 25, 2026).

Pandora is a quiet mission by NASA’s standards, and that is the point. The Astrophysics Pioneers line was created to fund focused science that flagship missions cannot deliver, on the argument that some questions need dozens of hours per target rather than a single snapshot. Pandora’s question is the one that underlies every transit-spectroscopy result published since 2002: how much of what we attribute to a planet’s atmosphere is actually the star’s surface?

The mission is now collecting data. The first peer-reviewed results are likely to land in late 2027 or early 2028, when the team has had time to reduce the first 12 to 18 months of stares and compare them against the existing Webb and Hubble baseline. If the contamination correction works as advertised on the well-characterized stars first, the team will extend the technique to the more interesting targets, including small cool stars whose habitable zones fall in the Sweet Spot for atmospheric characterization.

The broader programmatic test is whether Pioneers as a line can deliver the science per dollar that the 2020 decadal review committee hoped for. Pandora is the first example the field will judge.

Nine of the most massive galaxies in the nearby young universe have just told astronomers that the way they weigh themselves on paper has been wrong, and the correction makes them three to four times heavier than the previous best estimates. The galaxies sit at redshift z roughly 0.7, so their light left when the universe was about six billion years old, and they have already stopped forming stars in any meaningful quantity. A team led by Chloe Cheng at Leiden University, working inside the JWST-IMFERNO program, used the Near Infrared Spectrograph on the James Webb Space Telescope to take spectra deep enough to pick out the absorption features of low-mass stars in these distant systems for the first time. The result, published in Nature Astronomy on 18 August 2026 as Cheng, Slob, Kriek et al. 2026, is that the most massive early galaxies have a bottom-heavy initial mass function (IMF): they make a much larger fraction of low-mass stars than the Milky Way does. The implication is uncomfortable: the galaxies JWST has been finding “impossibly early” at z greater than 10 are now under even more pressure to have grown absurdly fast.

Astronomers measure the masses of galaxies the way a tax accountant estimates a person’s wealth from a bank statement: by counting the bright signals and assuming the rest scales the way it usually does. For galaxies, the “bright signals” are the few massive stars that dominate a spectrum, and the assumption is the IMF, the relative number of stars of different masses that a population of new stars produces. In the Milky Way and its immediate neighbourhood, the IMF has been calibrated against direct star counts: there is a fixed proportion of stars born above and below one solar mass, and that proportion is consistent across star-forming regions. Apply that same IMF to a distant galaxy and you can convert its total light into a stellar mass.

The problem is that the low-mass stars dominate the mass but barely contribute to the light. In the Milky Way, stars below about 0.7 solar masses make up roughly half the stellar mass but contribute only a few percent of the optical luminosity. Their presence has to be inferred. As the Leiden University press release frames it, “the brightest stars would be the skyscrapers you can immediately see from far away,” and the question has always been how many ordinary houses are hidden behind them.

JWST-IMFERNO answered that question for nine galaxies that finished forming their stars roughly six billion years ago. According to the team’s spectral fits, the two oldest galaxies in the sample carry so many low-mass stars that their true stellar masses are three to four times higher than the Milky-Way-IMF calculation would suggest. Joel Leja at Penn State, a co-author, told the Penn State press office that these systems have “three or four times more mass than we expected.” That correction pushes the most extreme galaxies further into territory galaxy formation models were already failing to reach.

The JWST-IMFERNO program (programme ID 5629, PIs Mariska Kriek, Aliza Beverage and Chloe Cheng) ran NIRSpec micro-shutter-array spectroscopy on May 3, 4 and 25 of 2025, taking extremely deep spectra of nine massive quiescent galaxies selected from the LEGA-C survey. LEGA-C, the Large Early Galaxy Astrophysics Census carried out with the VIMOS spectrograph on ESO’s Very Large Telescope, had already provided optical-wavelength spectra deep enough to measure stellar ages and metallicities for galaxies at z around 0.6 to 1.0. JWST’s NIRSpec extends the wavelength coverage into the near-infrared, where the absorption features that diagnose the low-mass stellar population live.

The sample was chosen to be representative of the most massive quiescent galaxies at that epoch: stellar masses above about 10 to the 11 solar masses, old stellar populations, low specific star formation rates. Cheng, finishing her PhD at Leiden, led the spectral fitting with state-of-the-art stellar population synthesis models. The procedure compares the observed spectrum against a grid of models that vary both the IMF shape and the standard population parameters (age, metallicity, dust). The Milky Way IMF, which has a characteristic mass near 0.2 solar masses and a slope that flattens at the low-mass end, served as the reference. The team found that the data prefer a steeper low-mass slope, in some cases a power-law index that produces many more stars below 0.5 solar masses.

A Space.com writeup by Robert Lea places the result in the broader context of the JWST “impossibly early” galaxy problem, the cluster of papers since 2023 reporting massive quiescent galaxies at z greater than 4 and even z greater than 10. The Cheng et al. result does not make that problem harder directly, because JWST-IMFERNO measured galaxies at z around 0.7, not the higher redshifts where the tension is sharpest. It does make it harder indirectly: if these z equals 0.7 descendants already carry a bottom-heavy IMF, then the IMF in their progenitors at z greater than 4 is likely to have been at least as bottom-heavy, and the stellar masses inferred for those progenitors from a Milky Way IMF would be too low by an even larger factor.

The paper appeared on arXiv on 28 January 2026 and passed peer review at Nature Astronomy in the spring and summer, with publication on 18 August 2026. The Leiden press release appeared the same day; the Penn State and Space.com writeups followed on 21 August, with ScienceDaily and phys.org coverage shortly after.

The technical content sits in three layers. The first is the spectral fitting: distinguishing a low-mass-star-dominated spectrum from a young, dust-reddened one requires very high signal-to-noise ratios and stable models. JWST-IMFERNO’s spectra reach signal-to-noise ratios near 100 per pixel, an order of magnitude deeper than anything previously published for galaxies at this redshift.

The second layer is the IMF parameterisation. The Milky Way IMF can be approximated as a broken power law with a characteristic mass near 0.2 solar masses and a slope that flattens below about 0.5 solar masses. A “bottom-heavy” IMF steepens that low-mass slope, so the same total light budget comes from a much larger number of low-mass stars. The Cheng et al. fits prefer a low-mass slope between roughly 2.5 and 3.0 in the targeted galaxies, versus about 1.3 for the Milky Way. The mass contribution from stars below 0.5 solar masses rises from roughly 30 percent in a Milky Way population to more than half in the bottom-heavy case.

The third layer is what the result does to cosmology. Stellar mass is the primary input to galaxy formation models: how fast galaxies convert gas into stars, how they grow their black holes, how they shut down star formation. If the most massive galaxies at z equals 0.7 are three to four times heavier than previously assumed, their stellar-mass densities are three to four times higher, their star-formation histories had to peak earlier, and the gas reservoirs that fed them had to be correspondingly larger. As the Leiden press release puts it, “models of galaxy formation must now explain how such enormous numbers of stars could have formed so early in the history of the Universe.”

The figure shows the nine JWST-IMFERNO galaxies as a 3-by-3 mosaic. Each panel is a postage stamp of one galaxy, with the characteristic yellow-red colour of an old, massive, quiescent stellar population. The visual sameness is part of the point: these are ordinary ancestors of today’s cluster ellipticals, and they share the bottom-heavy signature.

A single JWST program has now turned the most uncertain part of an extragalactic mass measurement (the contribution of stars too faint to see) from an assumption into a measurement. For nine massive galaxies at z roughly 0.7, the IMF is not the Milky Way’s. The two oldest galaxies in the sample are three to four times heavier than the old calculations said. The next JWST cycles will extend IMFERNO to higher redshifts, fainter galaxies, and galaxies with different star-formation histories. If the bottom-heavy signature persists, the textbook mass functions of early galaxies will be redrawn, and the timeline by which the universe assembled its first massive galaxies will be shorter than any current model predicts.

A heavy-water signature in the third interstellar visitor on record is rewriting what astronomers thought they knew about how comets form in other planetary systems. The comet 3I/ATLAS, which swept past the Sun in late 2025 on an unbound hyperbolic trajectory, carries roughly one deuterium atom for every hundred hydrogen atoms in its water ice. That is several times the ratio measured in any comet born in our own solar system, and it sits in territory that astronomers have struggled to explain with models tuned to the chemistry of nearby star-forming regions. A new analysis by a team led by Kenji Furuya of the RIKEN Pioneering Research Institute shows that the heavy-water fingerprint fits a comet that condensed out of a metal-poor molecular cloud, one older and more pristine than the cloud that gave the Sun its comets.

Why this matters goes beyond a single visitor’s biography. Interstellar objects are the only samples of other planetary systems that pass through the inner solar system on timescales short enough to study in detail. ʻOumuamua, discovered in 2017, was too faint and too dry to give up much of its chemistry. Borisov, the second confirmed visitor in 2019, was active enough to reveal carbon-based molecules but stayed below the brightness threshold for the most demanding isotopic work. 3I/ATLAS, the third confirmed interstellar object, found by the ATLAS survey on 1 July 2025, was bright enough to feed both the Very Large Telescope’s UVES spectrograph on Cerro Paranal and the James Webb Space Telescope, producing the first carbon, nitrogen, and water isotopic ratios measured in an interstellar comet. Those three numbers together, especially in a comet that has now left the inner solar system, are the closest astronomers will get to handling material from a protoplanetary disk around another star.

The story behind the heavy-water result runs back through several papers and one stubborn measurement. Earlier in 2026, Opitom and colleagues used UVES between 6 and 26 December 2025 to measure a carbon-12 to carbon-13 ratio of about 151 and a nitrogen-14 to nitrogen-15 ratio near 363 in the comet’s cyanogen (CN) gas, both well above the values typical of solar system comets. The carbon-12 to carbon-13 ratio sits closer to what models predict for the outskirts of an old, metal-poor protoplanetary disk. The JWST measurements that followed returned the heavy-water ratio itself, about 1% deuterium to hydrogen, which is roughly 50 times the ratio measured in a typical solar system comet and significantly higher than the values seen in nearby low-mass star-forming regions. The result was the third isotopic anomaly the comet had handed astronomers, after the carbon and nitrogen measurements, and it tied together two otherwise unrelated puzzles in a single chemical fingerprint. Furuya’s team, reporting in The Astrophysical Journal Letters, asked a deceptively simple question: can a low-metallicity origin explain both the carbon and the water isotopic signatures simultaneously? The same Opitom result was also reported by Sci.News the day the Nature Astronomy paper appeared.

The answer, from a grid of gas-ice astrochemical models spanning the cloud-to-core stages of star formation, is yes. The models vary four parameters: gas density, the strength of the interstellar ultraviolet radiation field, the cosmic-ray ionization rate, and the cloud’s metallicity (the abundance of elements heavier than helium, which astronomers treat as a proxy for how enriched the gas is by earlier generations of stars). The team tracked the chemistry of water and deuterated isotopologues from the diffuse cloud phase through the dense prestellar core, solving for the gas temperature at every step. The water D/H ratio observed in 3I/ATLAS is most readily reproduced at sub-solar metallicities, roughly half the Sun’s complement of heavy elements or less, and at relatively high cloud densities near 10,000 particles per cubic centimeter. Two of the four input parameters matter less: the ultraviolet field strength and the cosmic-ray ionization rate, provided the latter stays below about 10^-15 per second.

The deep dive into why metal-poor conditions pump up deuterium centers on a piece of interstellar chemistry that only happens in the cold. In molecular clouds at around 10 Kelvin, cosmic rays ionize molecular hydrogen and produce triatomic hydrogen ions (H3+). These ions can swap a proton for a deuteron when they collide with the common deuterated hydrogen molecule HD, producing H2D+ and ordinary H2. At cold temperatures the reverse reaction does not have enough energy to proceed, so deuterium becomes trapped in H2D+ until an electron recombines with it and frees a deuterium atom. That deuterium atom can then bond with oxygen to form HDO, heavy water, and from there normal water ice that inherits an unusually high D/H ratio. Three properties of a metal-poor environment amplify the effect. Less carbon monoxide means less H2D+ destruction, since CO readily reacts with it. Less water photodissociation by ultraviolet photons means a smaller flood of atomic hydrogen that would dilute the ratio. A modest cosmic-ray ionization rate keeps the reverse reaction from putting deuterium back into the more stable HD form. With all three effects turned on, the models produce D/H ratios near the 1% observed in 3I/ATLAS without invoking any exotic new physics. The same chemistry explains a related puzzle: the carbon-12 to carbon-13 ratio, which JWST measured earlier in 3I/ATLAS at somewhere between 123 and 191 depending on which carbon-bearing molecule was observed, is also a natural product of a metal-poor cloud. Galactic chemical evolution predicts that older stars, which formed before many supernovae had enriched the interstellar medium, should leave behind a higher ratio of carbon-12 to carbon-13 in their protoplanetary disks, simply because the heavy isotopes that would normally reset the balance had not yet been produced in large quantities.

The team’s robustness check is just as telling. They compared the D/H ratio of methane to that of water in 3I/ATLAS and in solar system comet 67P/Churyumov-Gerasimenko. The absolute deuteration of methane in 3I/ATLAS is around 3%, an order of magnitude above the 0.2% in 67P, but the ratio of methane deuteration to water deuteration stays close between the two comets. The chemistry that controls relative fractionation between water and methane is insensitive to the metallicity of the parent cloud, even when the absolute fractionation is not. That convergence is a quiet vote of confidence in the low-metallicity story.

The takeaway is specific and it sets up the next observation rather than closing the field. The carbon, nitrogen, and water isotopic ratios in 3I/ATLAS together describe a comet that condensed around a star several billion years older than the Sun, in a region of its disk where heavy elements were scarce and water ice picked up an outsized share of deuterium before the disk even began to form planets. The comet is now too faint and too distant for any current facility to repeat these measurements at higher signal-to-noise, and 3I/ATLAS’s perihelion passage on 29 October 2025 is now nearly a year in the past. The next interstellar visitor will eventually arrive, but until then, 3I/ATLAS remains the only sample astronomers have from a metal-poor protoplanetary disk, and the heavy-water ratio is the clearest handle on what that disk looked like.