Moon Europa.

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Researchers at the University of Ottawa have been testing an alternative cosmological model that describes a universe approximately 26.7 billion years old and seeks to explain observations without invoking dark matter or dark energy.

The framework is called CCC+TL. Its proposed endent prediction; the standard cosmological estimate is about 13.8 billion years.

CCC+TL stands for “covarying coupling constants plus tired light.” It allows certain physical constants to evolve together over cosmic time and attributes part of the redshift of distant light to photons losing energy during their journey. Cosmic expansion also contributes to the redshift. Combining these effects changes how observed redshifts translate into distances and cosmic ages, giving early galaxies considerably more time to develop within this framework.

The study highlighted in the announcement, published in Universe, examines Big Bang nucleosynthesis: the formation of helium, deuterium and other light nuclei in the early universe. The authors find that CCC+TL can preserve the standard model’s predicted abundances if nuclear reaction rates and neutron decay rates scale together with the altered expansion rate. Their calculations then produce nearly identical abundances. This agreement depends on those coordinated changes. Adopting a lower baryon density can reduce the longstanding lithium discrepancy, but simultaneously produces too much deuterium.

A separate paper examines galaxy rotation using the SPARC database, which contains 175 disc galaxies. A modified version of the CCC prescription reproduces rotation curves with performance comparable to MOND fitted individually to each galaxy. This extends the framework’s application to galactic dynamics, although fitting rotation curves alone cannot establish which explanation of the gravitational discrepancy is correct.

The researchers have also explored gravitational lensing in the Bullet Cluster. Their preliminary model produces additional gravitational effects concentrated around the galaxies, resembling the observed separation between the lensing signal and the hot gas. The paper acknowledges that this resemblance partly follows from constructing the extra-gravity profiles around member galaxies. A full comparison using the observed positions of multiple lensed images remains a further step.

Other tests remain at different stages of development. A supernova time-dilation analysis is still under review, while the cosmic microwave background analysis announced by the team has not yet been published. The cautious interpretation is that these studies provide conditional consistency checks and reasons for further investigation. They have yet to establish a revised age for the universe or a comprehensive replacement for ΛCDM.

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Astronomers using early data from the Vera C. @VRubinObs Observatory have identified 2026 ED138, a large object beyond Neptune that could qualify as a dwarf planet. It currently lies about 46 astronomical units from the Sun, roughly 6.9 billion kilometres. The discovery was , although further observations are needed to establish its size and physical properties.

Matthew Holman identified the object on 13 October using software developed with Kevin Napier to connect separate detections of moving objects. Mario Jurić then recovered additional observations in Rubin’s data, while searches of other surveys uncovered images dating back to 2016. That archival material gives astronomers more than a decade of observations with which to calculate its orbit. An object can appear in telescope images for years before anyone recognises that those detections belong to the same body.

The estimated diameter is between approximately 600 and 1,500 kilometres. This considerable uncertainty comes from its unknown surface reflectivity, or albedo. At a given distance, a smaller object with a reflective surface can appear as bright as a larger object with a darker surface. The often-mentioned diameter of around 1,000 kilometres therefore depends on an assumed albedo. Follow-up measurements could narrow that range, including observations of a stellar occultation, when the object passes in front of a distant star.

An icy body of this size could have enough gravity to become approximately rounded, one of the requirements for dwarf planet status. Under the International Astronomical Union’s definition, a dwarf planet orbits the Sun, has sufficient self-gravity to achieve a nearly round shape, has not cleared its orbital neighbourhood and is not a satellite. ED138 remains a candidate while its properties are investigated.

ED138 was found against a crowded background of Milky Way stars, which probably helped it escape earlier searches. Rubin’s repeated observations and tracking algorithms allowed researchers to identify its movement through that field. Studying such objects helps reconstruct the early Solar System: their orbits and surface compositions preserve evidence of how the giant planets migrated and redistributed smaller bodies beyond Neptune.

🎃 rubinobservatory.org/es/news/rubin-…

The stars and gas in a galaxy are constantly moving. In galaxies such as the Milky Way, much of that motion is organised into rotation around the galactic centre. Understanding where this rotation comes from requires looking back to the formation of galaxies, when gravity began matter into growing structures.

The early universe contained small differences in density, and the regions that would become galaxies had irregular shapes and uneven surroundings. Nearby concentrations of matter pulled more strongly on some parts than others, exerting gravitational torques that gave these regions angular momentum. Gas arriving along cosmic filaments and encounters between growing structures supplied additional angular momentum. When two systems merged, some of their orbital motion could become internal rotation in the resulting galaxy.

Angular momentum describes motion around a point or axis and depends on mass, velocity and how matter is distributed. Without an external torque, a system’s total angular momentum remains constant. If its matter contracts towards the rotation axis, its rotation can therefore become faster. Conservation explains how existing rotation changes during contraction; the initial angular momentum comes from the system’s formation and interactions.

Gas also behaves differently from stars and dark matter. It can collide, heat up and radiate energy, allowing it to settle into a thinner configuration. Its angular momentum limits how far it can collapse towards the centre and helps determine the size of the resulting disc. Stars born within that disc inherit much of the gas’s orbital motion, producing a population that largely travels around the galaxy in the same direction. Simulations show how cooling and the alignment of incoming gas contribute to the formation of thin stellar discs.

Subsequent evolution can change this organisation. Mergers redistribute angular momentum between stars, gas, dark matter and material expelled into the surroundings. Their effects depend on the masses, gas content and orbital orientations of the galaxies involved. Some elliptical galaxies retain substantial ordered rotation, while others have very little overall rotation and contain stars moving on orbits with many different orientations. The fact that their stars are moving does not necessarily mean that the galaxy has a strong collective spin. Observations distinguish these different populations through detailed maps of stellar velocities.

Spiral arms have their own dynamics. In density-wave models, stars and gas can move through regions of enhanced density rather than remaining permanently inside the same arm. Gas becomes compressed as it encounters these regions, encouraging the formation of young stars that make the arms particularly conspicuous. The visible spiral pattern and the orbital motion of individual stars therefore need to be distinguished.

The central supermassive black hole contributes to the gravitational field, but its influence dominates mainly in its immediate neighbourhood. Across most of a galaxy, stellar and gas orbits respond to the combined distribution of stars, gas and dark matter. The black hole contains only a small fraction of the galaxy’s total mass.

Measuring orbital speeds also reveals information about that mass distribution. In the outer regions of many spiral galaxies, speeds remain higher than the observed stars and gas can explain under standard gravity. Extended dark matter haloes provide the standard explanation for this discrepancy. However, approximately constant orbital speed does not mean constant angular speed: a star farther out travels around a larger orbit and takes longer to complete it. Our solar system, for example, takes roughly 230 million years to orbit the Milky Way’s centre.

For decades, astronomers have been trying to understand why some massive stars contain significantly more helium at their surfaces than stellar evolution models predict. A new study led by researchers at the Instituto de Astrofísica de Canarias (@IAC_Astrofisica) provides l evidence that the explanation lies in the evolutionary history of binary star systems.

Massive stars, particularly those of spectral type O, are among the hottest, most luminous and shortest-lived stars in the universe. Their intense nuclear fusion processes gradually alter their internal chemical composition, converting hydrogen into helium and, at later evolutionary stages, producing heavier elements. However, the chemical composition we measure through spectroscopy comes primarily from their outer layers. Explaining how material processed deep inside a star reaches its surface has remained a significant challenge, especially when the observed helium abundance exceeds the predictions of conventional single-star models.

An international team examined 45 spectroscopic binary systems containing O-type stars, using observations from the IACOB, MONOS and OWN projects. These are systems in which the orbital motion reveals the presence of a companion, even though its light cannot be directly distinguished in the observed spectrum. The researchers compared surface helium abundances with orbital properties, including periods and eccentricities, and identified a striking relationship.

Seven of the 45 systems showed enhanced helium abundances, and all seven had orbital periods shorter than approximately 15 days. They were also classified as runaway stars, meaning their motion differs significantly from that of the surrounding stellar population. Four displayed relatively high orbital eccentricities, while the remaining three showed ellipsoidal variations associated with tidal distortion. The statistical relationship between helium enrichment and these orbital characteristics was particularly strong, suggesting that the stars share a common evolutionary mechanism.

The most plausible explanation involves mass transfer between stellar companions. In a massive binary system, the initially more massive star evolves faster and eventually expands enough for material to flow towards its companion. As the interaction progresses, helium-enriched material from deeper layers of the donor can be transferred onto the receiving star, changing the chemical composition of its surface. The receiving star may therefore appear unusually helium-rich even though that enrichment did not originate entirely from its own internal evolution.

The donor star can subsequently lose much of its outer envelope, becoming a stripped star, and may eventually collapse into a neutron star or black hole. If a supernova occurs, the associated mass loss and possible asymmetric kick can modify the binary's orbit and give the surviving system an unusual velocity. This provides a possible explanation for the relationship between helium enrichment, orbital eccentricity and runaway motion. One of the systems included in the analysis is Cygnus X-1, a well-known binary containing a stellar-mass black hole.

The researchers emphasise that these observations strongly support binary interaction as the dominant explanation for helium enrichment in the studied O-type stars, although the evolutionary histories of individual systems have not been directly reconstructed. The precise nature of several unseen companions also remains uncertain, and further observations will be necessary to distinguish between stripped stars and compact remnants.

The implications extend beyond the chemical composition of individual stars. Binary interactions influence stellar masses, rotation rates, supernova progenitors and the formation of compact objects. Improving these evolutionary models is therefore essential for understanding the populations of neutron stars and black holes, the production of gravitational-wave sources and the chemical evolution of galaxies.

Perhaps one of the most useful consequences of this research is that surface helium enrichment could become an observational signature of previous binary interactions. A star may retain chemical evidence of a companion's influence long after that companion has become difficult to detect or the original system has been disrupted. This gives astronomers an additional way to reconstruct the evolutionary histories of massive stars from the properties we can still observe today.

🍁 arxiv.org/pdf/2608.05421

Imagine rearranging Earth into a broad, flat disk while keeping its present mass and the laws of physics we know. To make the experiment reasonably clear, suppose the disk has a roughly uniform distribution of rock, dimensions comparable to those of a terrestrial planet, and slow need something extraordinary to hold it in that shape temporarily. Under those assumptions, we can work out how gravity would affect people, oceans and air, and why the disk would deform once its support disappeared.

Gravity acts between every piece of matter and every other piece. The gravitational pull you feel comes from the combined attraction of the entire planet. Each part contributes a force with its own strength and direction, and those contributions add together. For a perfectly spherical, spherically symmetric planet, the external gravitational field behaves exactly as though all its mass were concentrated at its centre. Earth is close enough to that arrangement for gravity near its surface to point approximately towards its centre. That is what defines “down” wherever you stand.

A disk has a different geometry. Directly above the centre of one face, the sideways contributions cancel by symmetry, leaving an attraction perpendicular to the surface. Move away from the centre, however, and that cancellation becomes incomplete. For the roughly uniform disk imagined here, gravity develops a component directed inward across the surface. Towards the outer regions, its direction becomes increasingly tilted relative to the ground. This follows from adding the attractions of the disk’s individual parts. Close to a disk, we cannot simply replace all that matter with a point at its centre and expect an exact answer.

That would change ordinary experiences. A hanging plumb line would point partly towards the disk’s interior. A dropped object would accelerate both towards the surface and inward. Walking towards the edge would require working against that inward attraction, so a geometrically flat road could demand the effort of an uphill walk. To stand comfortably, you would need to align your body against the local direction of gravity, which would no longer be perpendicular to the ground everywhere. The strength of your weight would also depend on the disk’s dimensions and mass distribution; preserving Earth’s total mass would not preserve present-day surface gravity at every location.

The oceans would respond to the same altered gravitational field. Water at rest settles onto an equipotential surface: a surface along which moving a small amount of water would not change its gravitational potential energy. Its surface is locally perpendicular to effective gravity. This is why “level” water can follow a curved planetary surface. On our hypothetical disk, water spread across a flat face would experience an inward pull and begin redistributing towards the central region. Its eventual surface would be curved, with its depth and extent determined by the amount of water, the underlying terrain and the disk’s gravitational field. A large central accumulation is a reasonable consequence of this model, although its exact appearance would require calculation.

The atmosphere would redistribute as well. Air remains around Earth because gravity binds it, while pressure differences help support it against that attraction. In the disk experiment, the direction and strength of gravity would vary across the surface, changing the pressure structure needed for balance. At comparable temperatures, air would tend to concentrate more strongly in the deeper gravitational potential towards the central region. The adjustment would produce air flows and change conditions across the disk. Predicting completely airless edges, however, would require additional assumptions about its dimensions, temperature and atmospheric mass. Flatness alone does not establish that outcome.

All of this assumes that something continues to hold the rocky disk in place. Without that support, the planet’s own material would respond to gravity too. Rock can preserve irregular shapes when the gravitational stresses are modest. Small asteroids can therefore remain elongated or angular. As a body becomes larger and more massive, its own gravity produces stresses that can overcome the strength of its material. Rock can fracture, deform and, under sustained pressure and suitable temperatures, flow. This is why a small stone can keep its corners while a planet cannot maintain an enormous, unsupported rocky extension indefinitely.

For an object with Earth’s mass and broadly planetary dimensions, a thin, slowly rotating disk would be far from mechanical equilibrium. Its material would rearrange towards a more compact, rounded configuration. Internal pressure would resist further compression, while gravity would continue acting throughout the body. The resulting balance is called hydrostatic equilibrium when pressure supports the material against gravity. A sufficiently relaxed, slowly rotating planet approaches a spherical shape because that geometry allows this balance to hold in every direction. Earth’s solid structure preserves mountains and other departures from equilibrium, but those are small compared with the planet itself.

Rotation modifies that balance. In a rotating frame, the centrifugal effect is strongest farthest from the rotation axis, favouring a wider equator. Earth is therefore slightly flattened at the poles and wider around its equator. Faster rotation can produce greater flattening, but it also changes the stability of the body. We could not arbitrarily increase the spin of an Earth-mass rocky planet and assume it would become a stable, extremely thin disk. Its angular momentum, internal structure and ability to remain gravitationally bound would all matter.

The deformation of our unsupported disk would release gravitational potential energy as matter moved into a more tightly bound arrangement. Some of that energy would become motion; collisions, friction and deformation would convert part of it into heat. Depending on the starting configuration, the process could involve enormous fractures, violent movements of rock and water, and substantial heating. An exact countdown or a particular explosion sequence requires a defined physical model. Radius, thickness, density, temperature, material strength and rotation all affect the evolution. A characteristic gravitational timescale can give an estimate, but a realistic account of the disruption and eventual settling would require a dynamical calculation.

The magnetic-field claim also needs care. Earth’s main magnetic field is generated by the motion of electrically conducting fluid in its outer core. Rearranging the planet would profoundly disturb that system, but the surface’s flatness alone does not tell us whether a magnetic dynamo could operate in the resulting interior. Nor does losing an internally generated magnetic field automatically remove an entire atmosphere. Venus provides a useful example: it has a very dense atmosphere despite lacking an Earth-like intrinsic magnetic field. Atmospheric escape depends on several interacting processes, including gravity, heating and interactions with the solar wind.

Earth’s nearly spherical shape is a physical consequence of its mass, its materials and its rotation. The same gravity that determines which way an object falls also governs how oceans settle and how the planet’s interior supports its own weight. Changing Earth into a disk would change all those relationships together. With ordinary rock, Earth’s mass and slow rotation, maintaining that flat shape would require a supporting mechanism capable of resisting forces that naturally drive the planet towards a rounded form.

Supermassive black holes existed when the universe was less than a billion years old, raising a difficult question: how did they acquire so much mass so quickly?

One possibility is that some began as unusually massive black holes formed inside dense star clusters. A larger ce the growth required to reach the enormous masses inferred for early quasars.

Webb has revealed environments where this process could have operated. In the Cosmic Gems arc, astronomers identified five compact star clusters seen when the universe was around 460 million years old. Firefly Sparkle contains ten clusters observed roughly 600 million years after the Big Bang.

Both galaxies are magnified by gravitational lensing: foreground galaxy clusters bend and amplify their light, allowing Webb to distinguish structures that would otherwise be too small and faint to study individually.

Within a sufficiently dense cluster, stars can collide and merge repeatedly. Successive mergers may produce a very massive star that eventually collapses into a black hole.

Whether this happens depends on the cluster’s mass, size and internal dynamics: stars must interact frequently enough for substantial growth to occur within their short lifetimes. Compact clusters therefore provide particularly favorable conditions for this formation route. Low abundances of elements heavier than helium also help stars retain mass by reducing losses through stellar winds.

Astronomers modeled stellar collisions and wind losses in these systems. They predict black holes of approximately 1,600–2,700 solar masses in Cosmic Gems and 180–810 solar masses in Firefly Sparkle.

Comparisons with existing simulations support their approach, although unknown cluster structures, rotation and binary populations introduce uncertainties. Webb has observed the clusters; the proposed black holes remain unconfirmed.

Such objects would occupy the intermediate mass range between ordinary stellar remnants and supermassive black holes. They would still need to grow substantially through gas accretion and potentially mergers. Forming relatively massive seeds early would make that subsequent growth easier, while the availability of surrounding material would help determine how far it could proceed.

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The #JWST has revealed massive black holes already present during the universe’s first billion years, raising questions about how they formed and grew so quickly. It has also discovered “little red dots,” compact, reddish sources whose physical nature remains under discussion. t with growing black holes embedded in dense gas, although their unusual properties leave room for several interpretations. Understanding these objects could help astronomers identify the conditions in which the earliest massive black holes developed.

A study investigates the role of stellar collisions in these environments. Stars rarely collide in our region of the Milky Way, but the exceptionally dense clusters present in the young universe could have experienced frequent encounters. At sufficiently low relative speeds, collisions can merge stars into larger objects.

Repeated mergers could eventually assemble an extremely massive star whose collapse would produce a substantial black hole, giving its subsequent growth a much larger starting mass.

The researchers combined an analytical model with conditions drawn from cosmological simulations and tested selected predictions using Monte Carlo calculations. For some cluster configurations, they estimated that stars could accumulate tens of thousands to around a hundred thousand solar masses.

They also examined clusters containing an existing black hole. Close to it, higher stellar velocities can make collisions destructive, releasing material that builds up a dense gaseous environment. This offers a possible source of the gas invoked in explanations of little red dots.

The results identify plausible physical conditions for these processes, while their connection to particular observed objects remains unconfirmed. The model simplifies stellar encounters and cluster evolution, and its gas estimates omit cooling and feedback. These uncertainties affect both the predicted stellar masses and the amount of gas retained.

More detailed calculations are needed to establish whether collisions can reproduce the observed properties of little red dots and explain a significant fraction of early massive black holes.

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The stars and gas in a galaxy are constantly moving. In galaxies such as the Milky Way, much of that motion is organised into rotation around the galactic centre. Understanding where this rotation comes from requires looking back to the formation of galaxies, when gravity began matter into growing structures.

The early universe contained small differences in density, and the regions that would become galaxies had irregular shapes and uneven surroundings. Nearby concentrations of matter pulled more strongly on some parts than others, exerting gravitational torques that gave these regions angular momentum. Gas arriving along cosmic filaments and encounters between growing structures supplied additional angular momentum. When two systems merged, some of their orbital motion could become internal rotation in the resulting galaxy.

Angular momentum describes motion around a point or axis and depends on mass, velocity and how matter is distributed. Without an external torque, a system’s total angular momentum remains constant. If its matter contracts towards the rotation axis, its rotation can therefore become faster. Conservation explains how existing rotation changes during contraction; the initial angular momentum comes from the system’s formation and interactions.

Gas also behaves differently from stars and dark matter. It can collide, heat up and radiate energy, allowing it to settle into a thinner configuration. Its angular momentum limits how far it can collapse towards the centre and helps determine the size of the resulting disc. Stars born within that disc inherit much of the gas’s orbital motion, producing a population that largely travels around the galaxy in the same direction. Simulations show how cooling and the alignment of incoming gas contribute to the formation of thin stellar discs.

Subsequent evolution can change this organisation. Mergers redistribute angular momentum between stars, gas, dark matter and material expelled into the surroundings. Their effects depend on the masses, gas content and orbital orientations of the galaxies involved. Some elliptical galaxies retain substantial ordered rotation, while others have very little overall rotation and contain stars moving on orbits with many different orientations. The fact that their stars are moving does not necessarily mean that the galaxy has a strong collective spin. Observations distinguish these different populations through detailed maps of stellar velocities.

Spiral arms have their own dynamics. In density-wave models, stars and gas can move through regions of enhanced density rather than remaining permanently inside the same arm. Gas becomes compressed as it encounters these regions, encouraging the formation of young stars that make the arms particularly conspicuous. The visible spiral pattern and the orbital motion of individual stars therefore need to be distinguished.

The central supermassive black hole contributes to the gravitational field, but its influence dominates mainly in its immediate neighbourhood. Across most of a galaxy, stellar and gas orbits respond to the combined distribution of stars, gas and dark matter. The black hole contains only a small fraction of the galaxy’s total mass.

Measuring orbital speeds also reveals information about that mass distribution. In the outer regions of many spiral galaxies, speeds remain higher than the observed stars and gas can explain under standard gravity. Extended dark matter haloes provide the standard explanation for this discrepancy. However, approximately constant orbital speed does not mean constant angular speed: a star farther out travels around a larger orbit and takes longer to complete it. Our solar system, for example, takes roughly 230 million years to orbit the Milky Way’s centre.

.@ESA_Euclid has identified 94 promising candidates for galaxies with polar structures: stellar components strongly tilted relative to the main galactic body.

Researchers found them by visually examining around 11% of the Q1 survey area using the telescope’s VIS instrument. The etric redshift of 0.93, extending the search well beyond the local Universe.

These systems could help explain how galaxies acquire external material and develop components with different orientations. Their classification remains provisional: measurements of stellar or gas motions are needed to confirm their polar nature.

Visual selection also introduces biases, and the sample cannot yet establish how common these galaxies are or how their population evolves.

🍁 arxiv.org/pdf/2610.34049

High-energy neutrinos reach Earth from some of the most energetic environments in the universe, but identifying their sources remains difficult. They interact so rarely with matter that most pass through our planet undetected. At the South Pole, IceCube monitors a cubic kilometre e light emitted by charged particles produced in occasional neutrino interactions. These observations allow researchers to estimate the neutrino’s energy and arrival direction, providing information about the event that produced it.

Active galaxies powered by accreting supermassive black holes are among the leading candidates. Their high-energy activity can produce both neutrinos and electromagnetic radiation. However, radiation can be absorbed before reaching us, making some sources difficult to identify with gamma-ray telescopes. Radio observations offer another way to investigate their activity, including changes in brightness that might accompany neutrino production.

A study compared @uw_icecube detections with the first two observing epochs of the Very Large Array Sky Survey. Conducted from New Mexico, VLASS repeatedly observes much of the sky, allowing astronomers to identify changing radio sources. The researchers searched for neutrinos arriving from compatible directions during intervals when these sources brightened.

They found more associations than expected from random coincidences. The excess was consistent with radio-flaring sources contributing approximately 13% of IceCube’s astrophysical neutrinos, although the estimate carries an uncertainty of about 10 percentage points. Around 90% of the associated radio sources lacked detections in gamma rays or X-rays. These remain candidate associations, rather than individually established neutrino sources.

The statistical evidence is still modest, at just above two sigma. As researchers explain, a comparable result could occur roughly once in 30 repetitions under a model with no underlying connection. More observations are therefore needed to establish whether the apparent relationship persists.

Timing also matters: the researchers found no significant excess when they compared positions without imposing a temporal connection. Further radio observations and more precise neutrino directions could strengthen the analysis, helping determine how much these variable sources contribute to the observed neutrino population.

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A study examines whether departures from a homogeneous universe could produce effects usually attributed to dark energy. The work investigates how small radial disturbances evolve within general relativity. The authors identify instabilities in a mathematical description of propose that the resulting departures from uniform expansion could provide a mechanism relevant to the acceleration inferred from astronomical observations.

The calculations assume spherical symmetry, matter with negligible pressure and a zero cosmological constant. Pressureless matter is a useful approximation during the matter-dominated era. Their reference solution is the spatially flat, matter-only Friedmann universe, and the analysis also incorporates Friedmann solutions with positive or negative spatial curvature. These assumptions define the setting in which the mathematical results apply.

To study stability, the researchers express the Einstein–Euler equations using a variable that combines radial distance and time. In these coordinates, the flat Friedmann solution becomes a fixed point, allowing them to investigate whether nearby configurations approach it or move away. They then expand the relevant quantities in powers of the radial variable. The time-dependent coefficients obey a hierarchy of ordinary differential equations, whose behaviour can be analysed at successive orders.

Within this framework, the authors identify a family of configurations that are underdense relative to the flat reference universe. At leading order, these agree with a negatively curved Friedmann model. Higher-order disturbances can grow and generate departures from that homogeneous evolution at intermediate times. The asymptotic analysis finds that the departures eventually decay, with the configurations approaching the same leading-order Friedmann behaviour at each fixed radius. This provides a mathematical setting in which expansion can temporarily differ from the homogeneous reference without introducing dark energy.

An important qualification concerns the relationship between the series expansion and solutions of the complete equations. The authors establish the behaviour of the coefficient hierarchy order by order. A formal series with well-defined coefficients at every order still needs to converge before it represents an actual spacetime solution. The paper explicitly leaves for future work the conditions on general initial data that would guarantee this convergence. Its results therefore distinguish an asymptotic analysis from the broader existence problem for the family of exact solutions.

The proposed connection with observations involves the relationship between luminosity distance and redshift, which astronomers use to reconstruct the expansion history. The authors discuss how the freedom in their initial conditions can modify the coefficients of this relation and potentially reproduce effects associated with dark energy. They also revisit comparisons from their earlier research. Establishing the cosmological relevance of this mechanism requires determining whether a physically admissible solution can reproduce the observations consistently across different measurements.

The spherical geometry introduces an additional requirement. To explain the near isotropy of the observed Universe, the Milky Way would need to lie sufficiently close to the centre of the relevant density and expansion pattern. A homogeneous Friedmann universe has equivalent spatial locations throughout its background geometry. The observational consequences of occupying a position within the proposed inhomogeneous configuration would therefore need to be quantified.

In their discussion, the authors argue that the instability may also matter for cosmologies containing a cosmological constant, since its contribution becomes negligible relative to matter sufficiently early. Assessing that interpretation requires care: gravitational growth already plays an essential role in standard cosmology, including the formation of galaxies and clusters. The physical significance depends on which disturbances grow, under what conditions and how they affect observable quantities.

The study develops a theoretical candidate for explaining dark-energy-like effects through inhomogeneous evolution within general relativity. Establishing it as a description of our Universe requires further mathematical existence results and a consistent comparison with supernova distances, the cosmic microwave background, baryon acoustic oscillations and the growth of structure.

🎃 royalsocietypublishing.org/rspa/article/4…

Astronomers using @ESO_Chile Very Large Telescope have identified an unusual arrangement of planetary debris around the white dwarf J1328−1450: two concentric rings of gas separated by a gap. A white dwarf is the compact stellar remnant left after a star has expanded into a r layers. Rocky objects that survive this evolution can subsequently break apart, supplying debris to a disc around the remaining star.

The team inferred the double structure from observations with the X-shooter spectrograph. Gas emits light at particular wavelengths, which shift according to its motion. In a rotating ring, material approaching us produces a blueshifted component, while material moving away produces a redshifted component. Together, these create two peaks in an emission line. In this system, several lines contain four peaks, consistent with two rings rotating at different speeds. The inner ring moves faster, producing a more widely separated pair of peaks; the outer ring contributes a narrower pair.

To explain the structure, the researchers propose that each ring contains a surviving rocky body whose interaction with surrounding dust generates gas. The inner object would be asteroid-sized, while the outer one could potentially be as large as Pluto or the Moon. These sizes are theoretical limits based on survival against tidal disruption; the bodies themselves remain unconfirmed. The rings also differ chemically: magnesium emission is detected only from the inner ring. This suggests material from distinct parent bodies, or from different layers of a differentiated object, such as a magnesium-rich mantle and a magnesium-poor crust. The spectral structure remained largely unchanged over more than two years of observations.

The study shows how complex planetary debris can remain after a star’s evolution into a white dwarf. Our Sun will eventually undergo this transformation, making systems like J1328−1450 useful for investigating possible outcomes for the surviving material in our own Solar System.

🎃 eso.org/public/archive…

Really sad to hear about Sir Patrick Stewart. From Shakespeare to Professor Xavier, he brought such warmth and conviction to his work. But for those of us who love space, there will always be something special about Captain Picard.

He made curiosity, patience and thoughtful g. Here was someone who listened, valued evidence and approached the unknown with a desire to understand. For a young person watching Star Trek, that was a wonderful example of what growing up could mean.

Science fiction can have a real place in how we discover science. A story gets you asking questions, and sometimes those questions stay with you through your studies and into your working life. His Picard gave young viewers a future worth being curious about, one where knowledge mattered and people from different backgrounds worked together.

I love that new generations will still get to meet him that way. There’s something comforting about knowing someone can press play tonight and discover all of this for the first time.

Thank you, Patrick. It was a privilege to watch you.
Rest In Peace Sir.

Astronomers using early data from the Vera C. @VRubinObs Observatory have identified 2026 ED138, a large object beyond Neptune that could qualify as a dwarf planet. It currently lies about 46 astronomical units from the Sun, roughly 6.9 billion kilometres. The discovery was , although further observations are needed to establish its size and physical properties.

Matthew Holman identified the object on 13 October using software developed with Kevin Napier to connect separate detections of moving objects. Mario Jurić then recovered additional observations in Rubin’s data, while searches of other surveys uncovered images dating back to 2016. That archival material gives astronomers more than a decade of observations with which to calculate its orbit. An object can appear in telescope images for years before anyone recognises that those detections belong to the same body.

The estimated diameter is between approximately 600 and 1,500 kilometres. This considerable uncertainty comes from its unknown surface reflectivity, or albedo. At a given distance, a smaller object with a reflective surface can appear as bright as a larger object with a darker surface. The often-mentioned diameter of around 1,000 kilometres therefore depends on an assumed albedo. Follow-up measurements could narrow that range, including observations of a stellar occultation, when the object passes in front of a distant star.

An icy body of this size could have enough gravity to become approximately rounded, one of the requirements for dwarf planet status. Under the International Astronomical Union’s definition, a dwarf planet orbits the Sun, has sufficient self-gravity to achieve a nearly round shape, has not cleared its orbital neighbourhood and is not a satellite. ED138 remains a candidate while its properties are investigated.

ED138 was found against a crowded background of Milky Way stars, which probably helped it escape earlier searches. Rubin’s repeated observations and tracking algorithms allowed researchers to identify its movement through that field. Studying such objects helps reconstruct the early Solar System: their orbits and surface compositions preserve evidence of how the giant planets migrated and redistributed smaller bodies beyond Neptune.

🎃 rubinobservatory.org/es/news/rubin-…

Wormholes are hypothetical solutions of general relativity in which spacetime itself forms a tunnel, or throat, connecting distant regions of the Universe, or, in some models, entirely separate universes.

In their simplest realizations, such as the Einstein–Rosen bridge, these rally stable: without support from exotic matter with negative energy density, they collapse almost instantly.

Many well-known traversable wormhole solutions therefore rely on violations of classical energy conditions. Observational studies, including the one discussed here (linked below), typically set aside the question of internal stability and instead concentrate on the external spacetime metric, how the geometry of spacetime affects light propagation, because this is what astronomical observations are sensitive to.

The recent theoretical work on electrically charged wormholes examines this external signature through gravitational lensing. Any compact spacetime curvature can bend and amplify light, but the detailed lensing pattern depends on the full metric, not simply on the presence of ordinary mass.

This point is subtle but important: some famous wormhole solutions, such as the Ellis–Bronnikov wormhole, are mathematically “massless” in the usual sense, yet still produce measurable gravitational effects because spacetime curvature itself guides light along nontrivial paths. The study implicitly operates within this broader relativistic framework, focusing on how geometry, rather than mass alone, shapes observable signals.

A central result concerns image multiplicity. Black holes, due to the presence of an event horizon and a photon sphere, can in principle generate an infinite sequence of increasingly faint relativistic images as light loops around the horizon multiple times. In contrast, the electrically charged wormholes considered here are restricted to producing either a single image or, at most, three.

This sharp limitation reflects the different causal and geodesic structure of a wormhole spacetime and provides a potentially clean observational discriminator.

The three-image configuration is particularly distinctive. In this case, the lens produces one extremely bright primary image and two much fainter secondary images with identical brightness.

In the language of observational astronomy, the two secondary images have a flux ratio of exactly 1, a highly restrictive condition that is rare in conventional galaxy-scale lensing, where asymmetries in the lens mass distribution almost always break such equality.

As expected from gravitational lensing theory, these twin images also have opposite parity: one is a mirror image of the other. This combination, unit flux ratio and opposite parity, constitutes a remarkably clean and recognizable lensing signature.

The extreme brightness of the primary image arises only under very specific conditions. Magnifications approaching 100,000 occur when the background source lies extremely close to a caustic of the wormhole lens, a region in the source plane where light rays are strongly focused and amplification formally diverges.

Such near-perfect caustic alignment is rare, but when it occurs, the wormhole would act as an extraordinarily powerful gravitational telescope, briefly elevating otherwise inaccessible distant objects into detectability.

Gravitational lensing is not the only observational handle on exotic compact objects. Another major probe is the shadow produced by strongly curved spacetime.

A true black hole possesses an event horizon that absorbs light completely, yielding a central region of near-total darkness. Wormholes lack an event horizon and instead feature a throat, which could allow some light to pass through or around the central region, potentially leading to residual brightness or a modified ring structure.

While the present study focuses on lensing rather than imaging, these shadow properties offer a complementary route for distinguishing wormholes from black holes.

Finally, the analysis concentrates on electrically charged, non-rotating wormholes, closely related to Reissner–Nordström–type solutions. Rotation, ubiquitous in astrophysical systems, would further modify both lensing and shadow signatures through frame-dragging and asymmetry. Extending these calculations to rotating, Kerr-like wormholes is a natural and necessary next step toward realism.

The study does not claim that wormholes exist, nor that any observed lens must be one. Its significance lies in providing precise, falsifiable predictions.

As lensing surveys become increasingly sensitive to image multiplicities, parities, and flux ratios, they offer a way to test whether spacetime ever arranges itself in forms more exotic than black holes, or whether wormholes remain elegant but unrealized solutions of Einstein’s equations.

☃️ arxiv.org/pdf/2207.05406

(Conceptual illustration of a wormhole showing the curvature of spacetime; this geometry is responsible for its potential gravitational-lensing effects.)

Betelguese... Betelguese... Betelguese 👻 🕷️

Betelguese’s Great Dimming in late 2019 and early 2020 was linked to an episode in which expelled material cooled and formed dust, obscuring part of the star.

Observations taken before the dimming had already revealed unusually cool structure of its extended atmosphere, consistent with a shock wave passing through the outer layers.

New research follows what happened afterward, using the Very Large Array and ALMA. Observations collected between 2021 and 2026 cover seven frequencies, from 22 to 485 GHz.

Different radio wavelengths reveal gas at different distances from the visible surface, allowing the team to examine both the temperature profile and the changing shape of the atmosphere.

The measurements show that the outer atmosphere has warmed since the unusually low temperatures recorded in 2019. The researchers found a brightness temperature, a temperature inferred from the radio emission, of around 3,500 K at approximately 2.7 stellar radii from the centre, falling to about 2,220 K closer in, at 1.2 stellar radii. This confirms a cool region between the visible surface and the hotter chromosphere, overlapping the molecular layer known as the MOLsphere. The radio measurements also indicate that relatively cool material remains mixed with hotter gas, which ultraviolet observations preferentially detect.

Another part of the investigation concerns Siwarha, Betelgeuse’s recently identified companion. Its roughly six-year orbit lies within the supergiant’s extended atmosphere, about 2.3 stellar radii from the centre. This orbital period offers an explanation for Betelgeuse’s long brightness cycle, alongside its shorter pulsation cycle of approximately 400 days. Earlier optical and ultraviolet spectroscopy had revealed changes in gas absorption and outflow that followed the expected orbital cycle. Those results support a model in which the companion’s gravity concentrates gas into a trailing, expanding wake as it moves through the atmosphere.

The new radio data add spatial evidence. Betelgeuse’s radio-emitting atmosphere appears slightly more elongated when Siwarha is expected to reach its greatest apparent separation, and rounder when the companion passes in front of or behind the supergiant. Siwarha itself is too faint to detect in these radio observations; the evidence comes from the changing shape of the surrounding gas.

These correlations are consistent with periodic atmospheric disturbances caused by the companion, although more observations across its orbit are needed to test the interpretation.

The study provides a way to investigate how a nearby companion interacts with the extended atmosphere of a massive, evolved star.

🎃 arxiv.org/pdf/2608.02847

Some of the stars in galaxy clusters lie outside the main bodies of individual galaxies, spread across a faint, extended component known as intracluster light. Many were stripped from galaxies through gravitational interactions. Their distribution and chemical composition can clusters assembled and how their galaxies have evolved.

Four coordinated studies using @ESA_Euclid first Quick Data Release examine this diffuse light, from the processing needed to preserve it in images to its shape, abundance and metallicity. A separate study develops faster simulations for assessing how Euclid’s spectroscopic measurements affect our reconstruction of galaxy clustering.

Measuring intracluster light requires particular care because it can be mistaken for background emission and removed during image processing. The methodological study develops a dedicated approach that suppresses background variations while preserving extended structures.

Tests that inject simulated clusters into real Euclid images show that the method can recover diffuse surface brightness with uncertainties of roughly 10% under the conditions examined. This provides a tested basis for the accompanying observational analyses.

A study of 205 clusters finds that the light becomes progressively more elongated away from the central galaxy. Its shape is broadly consistent with halo shapes inferred from gravitational lensing, supporting its usefulness as an indirect tracer of cluster structure. It’s also more closely aligned with the central galaxy than with the distribution of satellite galaxies. These measurements concern the projected stellar light; they don’t directly map the full three-dimensional dark matter distribution.

Another analysis examines approximately 300 clusters between redshifts 0.2 and 1.5. Under the study’s measurement definitions, intracluster light accounts for about 20% of the total cluster stellar light. At fixed cluster mass, that fraction remains approximately constant across the observed redshift range.

This suggests that a substantial diffuse stellar component was already present at earlier epochs. It doesn’t mean individual clusters stopped evolving: the sample compares different systems rather than following the same clusters through time, and the measured fraction depends on wavelength.

The metallicity study combines measurements from 168 clusters to trace their average stellar populations out to around 300 kiloparsecs. The diffuse light becomes bluer than the central galaxy, and stellar population models indicate lower abundances of elements heavier than helium.

This supports a formation scenario in which tidal interactions remove relatively metal-poor stars from the outskirts of massive satellite galaxies. The colour gradient is well established, but converting colour into metallicity depends on the adopted stellar population models.

The fifth paper addresses a different challenge: understanding which galaxies enter Euclid’s spectroscopic sample and how redshift errors affect clustering measurements. Its FastSpec and Pypelid tools reproduce key aspects of the observing and analysis process without requiring full pixel-level simulations. In the baseline simulated selection, redshift purity reaches 74% and completeness 45%, with improvements when photometric colours are included.

These are simulated performance estimates, not measurements of the final survey’s performance. The simplified noise model still omits residual contamination from overlapping spectra and some artefacts already seen in early data.

Together, these studies improve both the recovery of faint stellar structures and the modelling of observational biases.

The spectroscopic simulation paper remains submitted with acceptance not yet confirmed.

👉 arxiv.org/html/2610.2968…

👉 arxiv.org/abs/2610.29683

👉 arxiv.org/abs/2610.29684

👉 arxiv.org/html/2610.2968…

👉 arxiv.org/abs/2610.26990

Point Nemo, also known as the "oceanic pole of inaccessibility," is the point in the ocean that is farthest from any land. It is named after Jules Verne's character Captain Nemo from "Twenty Thousand Leagues Under the Sea." Point Nemo is located in the ... 1/

Astronomers using @almaobs have obtained a detailed view of a dense concentration of gas and dust that could help explain how massive stars begin to form.

Known as C2c1a and nicknamed the “dragon egg,” it lies within the Dragon Cloud, an infrared-dark molecular cloud ght-years away. Earlier observations had already identified it as a promising candidate for a massive stellar core at a particularly early stage of development.

Massive stars, generally defined as those with at least about eight times the Sun’s mass, develop in dense environments where gravity, turbulence, magnetic fields and radiation interact. As they grow, their radiation begins to alter the surrounding gas, making it difficult to reconstruct the conditions that existed before star formation started. Finding a sufficiently young object allows astronomers to investigate how material gathers before this activity becomes dominant.

One central question is whether a massive star begins inside a core that has already accumulated much of the material it needs, or whether a smaller initial object grows substantially by drawing gas from its wider surroundings.

A massive, starless core would provide an important test of the first possibility, but convincing examples have proved difficult to establish. An apparently single object can reveal several smaller condensations when observed more closely, while a deeply embedded protostar can remain difficult to identify.

The new observations resolve six components across the region. Its brightest central component, C2c1a(a), nevertheless remains a single emission peak down to a resolution of approximately 175 astronomical units, with an estimated compact radius of about 87 astronomical units. One astronomical unit is the average Earth–Sun distance. These measurements describe the emitting material around the possible forming star.

Determining its mass requires knowing the dust temperature. Warmer dust emits more strongly per unit mass, so the same measured emission can imply different amounts of material depending on the assumed temperature. Dust opacity introduces another uncertainty, because sufficiently opaque material can conceal emission from deeper layers. These are fundamental limitations when using dust radiation to measure the properties of embedded objects.

In this case, temperature assumptions and the spatial scale examined produce mass estimates ranging from roughly two to thirty solar masses. A central brightness temperature near 40 kelvin, compared with earlier measurements of much colder surrounding gas, also indicates that the structure cannot be described adequately by a single uniform temperature.

The team found little molecular-line emission at the centre and no outflow that could be confidently associated with it. Both findings are compatible with a very young object, although dense dust could obscure activity and a weak outflow could escape detection. The surrounding cold material provides a much larger potential supply of gas for further growth. The study therefore leaves open whether the central source is still prestellar or already contains a very young protostar.

👉 share.google/KNIFa74mFKUZUM…