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In a basement lab at Ben-Gurion University of the Negev, a cloud of about 20,000 rubidium atoms has just answered a question physicists have been asking for nearly a century. Cooled to a few nanokelvin above absolute zero and held still by microscopic wires on a fingernail-sized chip, the atoms were nudged into a quantum superposition in which one half of the cloud rose a few micrometres and fell back under gravity while the other half stayed put. When the two halves were brought back together, the interference pattern between them showed a clean phase shift, and that phase shift matched Einstein’s prediction to within 2.5 percent.

The result, published in Science Advances on 2 September 2026 by Dobkowski, Folman, Penrose, Vedral, Schleich and a dozen other collaborators, is the first direct measurement of the quantum phase accumulated by a freely falling particle. It is also a fresh check on Einstein’s equivalence principle, the assumption that gravity disappears for an observer in free fall. The principle works fine for billiard balls and spacecraft. Until now, no one had checked whether it still works when the falling object is in a quantum superposition of two places at once, which is what the Ben-Gurion group, along with partners at Oxford and Ulm, set out to do. That the check matters at all is because general relativity and quantum mechanics describe the universe with completely different mathematical machinery, and they have resisted every attempt to combine them for almost a century. Most attempts to unify the two assume, implicitly, that the equivalence principle still applies at quantum scales, and this result is the first empirical reason to believe that assumption is correct.

Building the right kind of interferometer took the Folman group years. Ordinary atom interferometers, which have existed since the early 1990s, can compare two paths that both involve motion, one slightly higher than the other or one slightly accelerated with respect to the other. What they cannot do is compare a path that is genuinely free of forces against a path that is held artificially still, which is exactly the situation an equivalence-principle test requires, as Ars Technica reported on 11 September 2026. The team called the new device the Quantum Galileo Interferometer, or QGI, in honour of Galileo’s original observations of free fall, and the underlying method is laid out in detail on arXiv.

Inside a glass cell held under vacuum, a few micrograms of rubidium-87 gas is cooled into a Bose-Einstein condensate, a quantum state in which all the atoms share a single wave function. The condensate floats about 113 micrometres beneath an atom chip, a flat substrate etched with microscopic current-carrying wires that paint the surrounding space with carefully shaped magnetic fields. The chip itself is mounted upside down, with the wires facing the atoms, so the magnetic gradient can levitate the condensate in place. The whole apparatus is small enough to fit on a desk, which is part of why a single lab group could afford to spend years getting it to work, but the measurement it produces has implications for the largest questions in fundamental physics.

The reason it took so long is that interference, the property the experiment depends on, is fragile. Interference only appears when there is no way, even in principle, to tell which path a particle took; any measurement that distinguishes the two paths destroys the quantum superposition and forces the particle to behave like a localised classical object. Wave packets that have fallen under gravity are moving fast, while stationary wave packets are not, and that difference in speed is itself information about the path, so a naive setup would never produce an interference pattern at all. Folman and his colleagues had to design a sequence of pulses that cancels the path information without cancelling the phase information they actually wanted to measure.

Once the atoms are ready, the experiment unfolds in four microwave and magnetic pulses, summarised in Figure 1 of the arXiv preprint. The first pulse puts every atom into a superposition of two spin states: one that feels the magnetic field and one that does not. A magnetic pulse then kicks the magnetically sensitive state upward, launching it on a ballistic arc, while the insensitive state stays put. A second microwave pulse swaps the roles: the rising atom becomes magnetically insensitive and falls freely under gravity, while the stationary atom becomes magnetically sensitive and is held hovering by a field tuned to exactly cancel its weight. A final magnetic pulse acts as a parachute, gently braking the falling atom so it lands back where it started, where the two halves of each atom can interfere. At their farthest apart, the two trajectories were about 7.5 micrometres apart and the longest free-fall time was about two milliseconds. The interference pattern at the end of each run depends on the phase that the falling path accumulated during its trip. The longer the fall, the more phase, and the chirp in those oscillations is the signature the theory predicts. As the team lengthened the fall duration, the measured phase grew in proportion to gT squared, exactly as general relativity predicts for a classical trajectory and as the equivalence principle predicts for a quantum one.

The interpretation is the part that makes the result satisfying rather than just technical. From the perspective of the falling atom, there is no gravity at all: it is in free fall, the way an astronaut is in orbit, and its wave should pick up no extra phase. From the perspective of the laboratory, the same atom is being pulled downward at 9.81 metres per second squared, and its wave should accumulate a phase proportional to gT squared. The two views should agree, and Einstein’s equivalence principle says they do. The QGI measures the lab-frame phase directly and shows that, to within the experiment’s precision, the falling quantum wave accumulates exactly the phase that gravity predicts. As The Brighter Side reported, the measurement is a checkpoint on the boundary between two theories that physicists are still trying to merge. The result does not say which, if either, will eventually have to give way, but it sets a baseline that future versions of the experiment will sharpen.

A first upgrade is already under construction at Ben-Gurion. The next-generation QGI is being designed to put nanodiamonds, particles roughly ten orders of magnitude heavier than rubidium atoms, into the same kind of superposition. Nanodiamonds sit in a mass range where several competing quantum-gravity models and collapse theories make different, falsifiable predictions, and putting a nanodiamond in superposition for any usable time has not yet been achieved. Folman told Ars Technica that his lab is already working on a design that he hopes will let the heavier experiment run within the next four or five years, though he was clear that it is “a very, very challenging project.” If it works, the team would have a direct laboratory test of the boundary between quantum mechanics and gravity in a regime where competing theories actually disagree.

In the meantime, the September result establishes something that has been assumed but not shown. When an atom falls, the quantum phase it picks up is the phase that gravity, applied classically, would predict. The equivalence principle, written down by Einstein in 1907 and tested for classical masses by Galileo, Newton, Bessel and Eötvös, has now been demonstrated, in a single careful experiment, for a particle that is in two places at once. The result does not resolve the long-standing tension between general relativity and quantum mechanics, but it removes one of the most reasonable doubts about how the two might eventually be unified: that the equivalence principle, which is foundational to general relativity, might quietly break at quantum scales. It does not appear to.

The two planets still growing inside the disk of PDS 70 have been some of the most photographed protoplanets in astronomy since the European Southern Observatory’s Very Large Telescope first imaged them in 2018 and 2019. Now the same system is offering up a second story, one that may explain where the water inside that disk came from. A team led by Aline Novais, a post-doctoral researcher in the Department of Physics at Lund University, reports in Nature Communications that PDS 70 shows variable sodium-line absorption matching the spectroscopic fingerprint of icy bodies sublimating as they swing past their star. The result, the authors say, makes PDS 70 the youngest known system in which exocomet activity has been proposed, and the first such case around a star whose temperature is close to the Sun’s. The story has been picked up by Universe Today and The Brighter Side of News.

PDS 70 sits about 370 light-years away in the constellation Centaurus. It is a K7 T Tauri star, slightly cooler and less massive than the Sun, and at roughly 5.4 million years old it has not yet settled onto the main sequence. Its surrounding protoplanetary disk is split by a wide gap, and inside that gap two gas giants, PDS 70 b at about 20.6 astronomical units and PDS 70 c at about 34.5 astronomical units, are still accreting material. The two planets were the first protoplanets ever directly imaged, and they have become a benchmark for what planet formation looks like while it is still happening. The ALMA image of the system, reproduced below, shows the bright orange dust ring and the dark gap carved out by the two forming gas giants (see the ESO image page for full credit and dimensions; the ESO artist animation shows the system in motion). The novelty in the new paper is not about the planets themselves but about what may be moving through the system alongside them, and what those moving bodies might be carrying inward.

The argument hinges on archival spectra. Novais and her co-author Alexandra Stockwell Murphy, also at Lund, went back to 52 high-resolution spectra of PDS 70 taken with the High Accuracy Radial velocity Planet Searcher (HARPS) on ESO’s 3.6-metre telescope at La Silla in Chile. The observations span 22 nights spread across 2018, 2019, and 2020. Most of the action is in 2018, when HARPS collected 18 epochs of data. Across those 18 nights, the team identified 43 variable neutral-sodium (Na I) absorption components moving at radial velocities from roughly minus 25 to minus 115 kilometres per second relative to the star. The lines were clumpy rather than uniform, sometimes covering only a fraction of the stellar disk, and they changed amplitude, number, and velocity from one night to the next. None of those properties fits a stable, smooth disk wind. All of them fit a stream of small bodies releasing sodium-bearing gas as they swing past the star and heat up.

That spectroscopic pattern is the same one astronomers have been cataloguing for decades around Beta Pictoris, the well-known A-type star surrounded by a debris disk where thousands of exocomet transits have been inferred from variable absorption lines. Beta Pictoris is hot, several times more massive than the Sun, and old enough that its inner system has long since been cleared. PDS 70 is young, cool, and still embedded in a gas-rich disk. The new result extends the exocomet phenomenon to a regime where the surrounding architecture is still being built.

The authors are careful about the word “evidence.” The variable Na I lines are consistent with sublimating planetesimals on highly eccentric orbits, but PDS 70 is also known to drive disk winds, and a sufficiently clumpy wind could in principle produce similar absorption. Novais and her colleagues ran a simple wind model and found that the sodium mass in the lines was substantially higher than the wind model predicted, that the velocity changes from night to night were too rapid for a steady outflow, and that the partial-disk coverage required a spatially confined source. The wind scenario could not be ruled out completely, because the star’s mass-loss rate and accretion properties are not well known. The exocomet scenario remains the preferred interpretation but is not yet confirmed. The authors also note that new observations taken in 2026 with the Ultraviolet and Visual Echelle Spectrograph (UVES, programme ID 0116.C-0329, PI A. Novais) show the activity is continuing, and a detailed analysis of that follow-up dataset is in preparation.

If exocomets are the right explanation, the second question is whether they can physically reach the inner disk at the rate the data implies. To test that, the team ran N-body simulations of planetesimals interacting gravitationally with the two known gas giants, and with a hypothetical third planet in a more distant orbit. In the two-planet case, on average 0.47 percent of the test particles crossed the planetary gap into the inner disk per million years; in the three-planet case, the figure rose to 2.9 percent. Translated into a flux, the simulations suggest that for every 10 Earth masses of planetesimals stored beyond the planets, between about 0.047 and 0.29 Earth masses of icy material could be crossing the gap per million years under the assumed configurations. That is a small fraction, but the inner disk has had millions of years to accumulate it.

The water question is what gives the result its broader reach. JWST’s Mid-Infrared Instrument (MIRI) had previously detected spectroscopic emission from gaseous water close to the star, inside the planetary gap. The origin of that water was not clear. Pure gas-phase synthesis in the disk is possible but slow, and the disk is also cool enough in its outer regions for water ice to be abundant on small bodies. The exocomet scenario links the two: comets perturbed inward by the giant planets sublimate as they pass through the inner disk, releasing water and other volatiles. “Our study suggests that comets may be responsible for transporting water to the inner parts of the planetary system, where planets can form, in the same way as in the early Solar System,” Novais said in a press release accompanying the paper. “It is reminiscent of a possible process in the early Solar System, in which comets may have helped to deliver water to the young Earth,” added Stockwell Murphy.

The comparison to the early Solar System is the point that resonates beyond this one system. The leading explanations for Earth’s water include late accretion of water-bearing asteroids, contributions from icy comets, and outgassing from the planet’s interior. None of those channels is easy to observe in action, because they happened more than four billion years ago. PDS 70 is young enough that the same channels may be operating now, and the planets are still growing, so the inner disk’s water reservoir is still being filled. If a Sun-like star can build a wet inner disk by shepherding icy bodies inward, the same process could have operated around the young Sun, and the question of where Earth’s water came from shifts from “which bodies delivered it” to “how much of it was cometary in the first place.”

The authors are clear that the next step is confirmation. The UVES follow-up is one avenue. Another is the ESO Extremely Large Telescope, now under construction in Chile, which will be able to image structures in the PDS 70 disk at much higher spatial resolution and look for individual transiting comets directly. If those observations find the same sodium clouds on the same highly eccentric trajectories, the exocomet interpretation will harden into a detection. For now, the result is a working hypothesis with strong circumstantial support: variable sodium in HARPS, an inner-disk water reservoir seen by JWST, and a dynamical simulation that says yes, the icy bodies in the outer disk can get there. PDS 70 may not be a complete answer to where Earth’s water came from, but it is the first place astronomers have caught the process plausibly underway in a system that looks, in temperature and architecture, uncomfortably like a very young copy of our own.

A decade after Type Ia supernovae earned half of the 2011 Nobel Prize in Physics for revealing that the expansion of the universe is accelerating, the same class of explosion is now driving the sharpest empirical challenge yet to the explanation behind that acceleration. In two companion papers posted to arXiv on 2 September 2026, a team led by University of Queensland PhD candidate Ryan Camilleri has stitched together 2,884 Type Ia supernovae drawn from the Pantheon+ and Dark Energy Survey five-year samples into a single, internally consistent compilation called Unite. When Unite is combined with cosmic microwave background and baryon acoustic oscillation data, the best-fit cosmology is no longer one with a constant dark-energy density. It is a flat universe whose dark-energy equation of state evolves with cosmic time, parameterised by today’s value w0 = -0.86 and a running slope wa = -0.60. That combination fits the combined data noticeably better than the cosmological constant, and the second paper reports that the host-galaxy mass corrections that make the sample consistent push the significance for time-evolving dark energy from 3.4 to 4.0 sigma relative to the older Pantheon+ result.

Why this matters is the size of the cosmological constant in the standard model and the conspicuous lack of a physical explanation for it. The standard Lambda-CDM picture of cosmology, described in detail in the Wikipedia dark-energy entry, treats dark energy as a fixed energy density, the cosmological constant, that fills space uniformly and does not change with cosmic time. That assumption has held up against every supernova sample, every galaxy-cluster count, and every CMB map for nearly three decades. It is also the assumption under which the accelerating expansion discovered in 1998 won a Nobel Prize. A growing body of independent probes, including the Dark Energy Spectroscopic Instrument’s measurement of the sound horizon from over six million galaxies and the second data release of the Dark Energy Survey, has begun to show small but coherent deviations from that picture. A w0-wa cosmology, in which the dark-energy density changes with the epoch, was long considered an unlikely complication that would die with more data. The Unite compilation is the first dataset large and internally consistent enough to push that complication past the four-sigma mark by combining supernovae with the CMB and baryon acoustic oscillations, two of the most precise cosmological probes available.

The story behind Unite runs back through the major supernova cosmology programs of the last fifteen years. Pantheon+ is the spectroscopic Hubble diagram assembled by Scolnic and collaborators from the PanSTARRS, Sloan, SNLS, and several earlier samples, totalling roughly 1,500 light curves; it became the workhorse sample for supernova cosmology after the original Pantheon release in 2018. DES-SN5YR is the Dark Energy Survey’s five-year photometric supernova program, which has now grown to be the largest homogeneous sample of Type Ia light curves from a single survey, with around 1,800 light curves of its own. Camilleri’s group combines the two into a single Hubble diagram by reanalysing Pantheon+ with the methodology that DES had already validated on its own data, then running both through the same bias corrections and selection cuts. The combined sample is 2,884 events with a consistent treatment of light-curve shape, colour, and host-galaxy stellar mass, and the team also redetermines host-galaxy stellar masses on a common framework that covers 98% of the sample. The earlier DES analysis of just the DES sample, reported in 2024, had already shown hints of a time-varying dark-energy equation of state. Unite shows the same hint pointing in a slightly different direction, and at a stronger significance when combined with the other probes. As Tamara Davis, the University of Queensland professor who oversaw the work, put it, two independent measurements now point in the same direction, which is what one looks for when the standard model starts to creak.

The deep dive into why supernova systematics matter so much centres on the host-galaxy mass step. Once a Type Ia supernova’s light curve has been standardised by its shape and colour, its peak brightness still depends, at the level of a few hundredths of a magnitude, on the stellar mass of the galaxy that hosted it. Brighter supernovae prefer galaxies with younger stellar populations, while fainter ones tend to land in older, more massive hosts. If that dependence is ignored, the standardised brightness comes out wrong, and the cosmological fit drifts. Earlier work by Vincenzi and collaborators compared the host-mass estimates used in Pantheon+ and DES-SN5YR, and showed that the choice of host-mass measurement alone contributes enough to the standardised magnitudes to flip the supernova-vs-CMB tension on or off. Lee and colleagues re-measure host masses for almost every supernova in Unite using aperture photometry and SED fitting on a single framework. Their masses differ from the values Pantheon+ released, partly because of a redshift-dependent internal inconsistency inside Pantheon+ that the new measurements expose. When the Pantheon+ subset of Unite is combined with baryon acoustic oscillations and the CMB, swapping in the new masses moves the significance for evolving dark energy from 3.4 sigma to 4.0 sigma. The same pair of papers also incorporates gravitational lensing magnification corrections, which slightly blur the standardisation but do not erase the deviation from a constant dark-energy density.

The combination itself is now decisive in a way that earlier work was not. For a flat universe with a constant equation of state, the SN-only fit returns a matter density of Omega_m = 0.310, very close to the standard value. For a flat universe in which the dark-energy equation of state evolves linearly with redshift (the so-called CPL parameterisation), the combined fit to supernovae, the CMB, and BAO returns Omega_m = 0.305, w0 = -0.86, and wa = -0.60, with a dark-energy figure of merit of 315. That value of w0 is less than -1, which means the dark-energy density was higher in the past than it is today. Wa is also negative, which means the dark-energy density is falling faster than the cosmological constant would imply. The combined dataset prefers this picture at the four-sigma level, and the paper’s own figure of merit shows a roughly 30% reduction in the w0-wa confidence region compared with Pantheon+ alone.

The takeaway is that the supernova case for evolving dark energy is now strong enough to be taken seriously, and the question is what kind of evolving. A dark-energy density that decreases with cosmic time is not the same as modified gravity, a quintessence field, or any of the more exotic options the literature considers, but it is no longer the cosmological constant either. The two independent DESI and supernova measurements, one based on sound waves in the early universe and one based on the brightness of stellar explosions in the late universe, now agree on the direction of the deviation, and the supernova side has just gotten both bigger and more internally consistent. The next year or two of data, from the still-pending third year of DES-SN5YR and from the rest of DESI’s first five-year BAO program, will tell whether the deviation grows or shrinks. If it grows, the 2011 textbook picture of dark energy is going to need a rewrite.

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.