Moon Europa. Image taken by #NASAJuno and processed by myself. #Europa #Jupiter #News #Astronomy #Science #NASA #Photography 🐘 mstdn.social/@GirlInSpace

Black holes are often described as objects that simply swallow anything that approaches them, but the reality of accretion is considerably more complicated. When a star passes close enough to a supermassive black hole, tidal forces can tear it apart in what we call a tidal disruption event, or TDE. Some of the stellar material forms an accretion flow around the black hole, while part of the matter and energy can ultimately be driven outward in powerful outflows or jets. These ejections, sometimes informally described as cosmic “burps”, do not come from inside the event horizon; they are produced by the extremely energetic plasma and magnetic fields in the region surrounding the black hole. A new study has now found evidence that the timing of these outflows follows a remarkably consistent physical rule. Astronomers studied twenty tidal disruption events using observations across radio, optical, ultraviolet and X-ray wavelengths, with ten systems providing sufficiently detailed data to model both the evolution of the accretion flow and the launch of the outflows. They found two distinct phases in which jets or outflows can appear. One occurs early, while the black hole is accreting matter at extremely high, sometimes super-Eddington rates. The second occurs much later, hundreds to thousands of days after the original disruption, when the accretion luminosity has declined to roughly 2% of the Eddington luminosity. That 2% value is particularly important because approximately the same transition has already been observed in stellar-mass black holes, systems only around several to tens of times the mass of the Sun. Supermassive black holes can contain millions or billions of solar masses, yet the transition between accretion states and jet production appears to occur at essentially the same fraction of the Eddington limit. This suggests that the coupling between the accretion flow and the production of jets may be scale-invariant: the same basic physics could operate around black holes separated by many orders of magnitude in mass. Tidal disruption events make this comparison possible because they effectively compress the evolution of a supermassive black hole accretion episode into a period that humans can observe. Normal active galactic nuclei may evolve through comparable changes over thousands of years, making it almost impossible to watch an individual supermassive black hole move through different accretion states. After a star is disrupted, however, its supply of material gradually decreases over months and years, allowing astronomers to watch the accretion flow evolve and determine when an outflow appears. The result could also explain why some tidal disruption events produce radio emission almost immediately while others remain quiet for years before suddenly brightening. Rather than being completely unpredictable, delayed jets may simply be waiting for the accretion rate to cross this critical threshold. Because radio observations allow astronomers to follow material moving outward from these systems, knowing approximately when this transition should occur could make future observing campaigns much more efficient. More importantly, the study provides observational evidence that black holes may follow a common accretion and jet-launching mechanism regardless of their mass. If larger samples confirm the relationship, tidal disruption events could become particularly useful laboratories for understanding not only how black holes grow, but also how the energy and matter they return to their surroundings influence the evolution of their host galaxies. 👉 share.google/N0QqYiaxkYWB3wx…

Two studies offer encouraging results for the search for life on Enceladus. One examines how material from its buried ocean reaches space; the other tests whether a terrestrial microorganism can remain active under some of the conditions expected there. Together, they strengthen the case for investigating this moon’s habitability and analysing its ejected ice particles for possible biological material. Enceladus releases ocean material through fractures near its south pole. Cassini sampled these plumes and detected salts and organic compounds. The new research suggests that droplets freeze gradually during their passage through the icy crust, allowing their dissolved constituents to accumulate in different regions. Subsequent fragmentation can produce grains with very different compositions, some containing particularly concentrated substances. This could help future instruments identify compounds that would be harder to detect in a more diluted mixture. The biological experiment explored another question: whether the ocean’s alkaline chemistry could prevent certain microbes from obtaining enough carbon dioxide for their metabolism. Researchers tested Methanothermococcus okinawensis, an archaeon from terrestrial hydrothermal environments that uses hydrogen and carbon dioxide to produce methane without requiring oxygen. In the simulated Enceladus environment, it continued growing and producing methane despite the scarcity of dissolved carbon dioxide, using hydrogen supplied by reactions between water and rock. These findings don’t establish that Enceladus is inhabited. A terrestrial organism’s response to selected laboratory conditions cannot tell us whether life originated in an extraterrestrial ocean. They do provide a stronger experimental basis for asking what could survive there. The sampling research also suggests that any microbial material might become concentrated in a small proportion of the ejected grains. A future spacecraft would therefore need to examine many particles individually to improve its chances of encountering such material. 👉 share.google/siWAtz3J4D4SSh3… 👉 science.org/doi/10.1126/scia…

New images captured by SMILE, a joint mission between ESA and the Chinese Academy of Sciences, show the entire auroral oval surrounding Earth’s North Pole in ultraviolet light, a global view that has not been seen in this way for around 18 years. The video also shows the ring becoming brighter during a geomagnetic substorm, when stored energy in the magnetosphere is suddenly released and particles are accelerated toward the polar regions. As these particles enter the upper atmosphere, they excite atmospheric gases and produce the auroral glow. Observing the aurora from space makes it possible to study it as a complete, dynamic structure rather than only from individual locations on the ground.

Cosmic inflation: what could have happened in the universe’s first moments? Look far enough in any direction and the universe has broadly similar properties. Individual galaxies are different, and matter gathers into clusters and filaments, but on sufficiently large scales the overall picture is remarkably uniform. Why should regions separated by such enormous distances have so much in common? Cosmic inflation offers a possible explanation. It proposes that the very early universe experienced an extraordinarily brief period of accelerated expansion, during which distances grew approximately exponentially. A small distance could double, then double again, repeatedly, in an exceptionally short time. To understand what that means, imagine two nearby points. As the space between them expands, they become farther apart even without moving locally through space. During inflation, that separation could have grown enormously. This is also why cosmologists can describe distant regions separating faster than light without breaking relativity: the local speed limit for matter and information still applies. One of the strongest motivations for inflation comes from the cosmic microwave background. This radiation has been travelling through the universe since around 380,000 years into its history, when conditions became cool enough for neutral atoms to form and light could travel freely over long distances. Today, we detect it across the sky at almost exactly the same temperature. That similarity needs explaining. If we trace cosmic expansion backwards using the hot Big Bang model without inflation, some of those regions wouldn’t have had time to exchange signals before releasing the light we now observe. Inflation allows them to have shared an earlier history, when they were close enough to interact, before expansion carried them far apart. It also helps explain why the geometry of space appears so close to flat. Think about how a small area of Earth’s curved surface looks almost flat to someone standing on it. Inflation would greatly increase the scale of any initial spatial curvature, making it difficult to detect within our observable region. Here, flatness refers to the geometry of three-dimensional space. We still can’t conclude that the entire universe is exactly flat or infinite. What could have driven such an expansion? Many models introduce a hypothetical field called the inflaton. A field is a physical quantity defined throughout space, and under the right conditions its energy could make cosmic expansion accelerate. We haven’t identified this field experimentally. Its properties remain one of the major unanswered questions. When inflation ended, the energy driving it would have been transferred into particles and radiation through a process called reheating. This would establish the hot, dense conditions described by the hot Big Bang model. The universe would continue expanding and cooling, eventually allowing atoms, stars and galaxies to form. The hot Big Bang describes that early thermal history extremely well, but it doesn’t establish whether space and time had an absolute beginning. There’s another reason inflation is so interesting: it offers an explanation for where cosmic structure came from. In inflationary models, tiny quantum fluctuations generated during that era are stretched to enormous scales. They provide the initial variations from which differences in density develop. Over time, gravity makes the slightly denser regions accumulate more matter. The first galaxies begin forming within the first few hundred million years, and structure continues growing over billions of years. According to this picture, the distribution of galaxies today ultimately traces back to processes operating at quantum scales in the very early universe. We can test that connection. The microwave background preserves information about the early variations, and observations such as those from Planck agree with several predictions of simple inflationary models. For example, the strength of the primordial fluctuations changes only slightly with scale, in a way those models can reproduce. Does that mean inflation is confirmed? We have meaningful indirect support, but we haven’t established a unique explanation for what happened. Different models predict different details, and some have already become difficult to reconcile with observations. An especially valuable clue would be primordial gravitational waves produced during inflation. They could leave a characteristic pattern in the polarisation of the microwave background. Finding it means separating an extremely faint signal from other effects, including Galactic dust and gravitational lensing. No confirmed inflationary gravitational-wave signal has been detected, and some models predict one too weak for present instruments. It makes ideas about an almost unimaginably early epoch accessible to observational tests. We can study ancient radiation and the distribution of galaxies, then check whether their properties fit the predictions. There’s still much we don’t understand, but we have concrete ways to investigate it.

The true size of Black Holes. © YT morn1415. #Science #Cosmos #BlackHole

Astronomers have obtained an unusually detailed view of a young giant planet interacting with the gas around it. Using @almaobs in Chile, a team studied WISPIT 2, a system roughly 430 light-years away that contains two young giant planets within a disk of gas and dust. The observations connect a directly imaged planet with disturbances in the motion of its surrounding gas, giving researchers a particularly valuable opportunity to test how growing planets reshape their environment. The outer planet, WISPIT 2b, has approximately five times Jupiter’s mass and lies about 57 times the Earth–Sun distance from the centre of the system. Hydrogen emission detected in earlier observations indicates that it’s still gathering material. Its companion, WISPIT 2c, is closer in, at roughly 14 astronomical units, with an estimated mass of about ten Jupiters. Both were already known before these latest ALMA observations. ALMA traced emission from carbon monoxide to map the gas and measure its motion. Near WISPIT 2b, the researchers found a distinctive disturbance that matches predictions for a planet interacting with its disk. This is the first confirmed association between this kind of gas-motion signature and a directly imaged planet. The observations also reveal a gap at the outer planet’s orbit, a depleted inner cavity and a ring of gas and dust between the two planets. The interpretation still requires care. The emission around WISPIT 2b extends across a region larger than expected for a small disk bound to the planet alone. The researchers suggest that several effects contribute, including spiral disturbances driven by the planet’s gravity, local heating and possibly a circumplanetary disk. Observations with finer velocity resolution will be needed to separate those contributions. There’s another interesting detail: WISPIT 2 contains two central stars. A separate spectroscopic study found a close stellar companion, with the pair completing an orbit in about 4.8 days. That makes this the first known circumbinary system with directly imaged protoplanets, offering a way to investigate how planets develop in a disk surrounding a stellar pair. 👉 share.google/JYFVaIF1mxuDu2p…

A black hole could separate from a surrounding bosonic field and leave a boson star behind, according to theoretical simulations by researchers at the University of Aveiro. The result concerns hypothetical black holes with “hair”, where an additional field exists outside the event horizon and contributes to the system’s properties. These configurations extend the familiar description of an isolated black hole through its mass, rotation and electric charge. Under suitable conditions, a rotating black hole can support a surrounding scalar field whose oscillation is synchronized with the horizon’s rotation. This connects two theoretical kinds of objects: black holes surrounded by bosonic fields and boson stars, configurations of those fields held together by gravity. The simulations examined systems where the surrounding field contains most of the energy. In the rotating model, the black hole moved outwards in a spiral, disrupted the field and absorbed most of it. A second model, involving electric charge and an interacting scalar field, produced a different outcome: the black hole was expelled, leaving an oscillating boson star moving in the opposite direction. What interests me most is the question this addresses: can a mathematically possible object survive disturbances? That’s essential when assessing whether such configurations could exist in the Universe. These simulations explore their theoretical behaviour; they don’t establish that nature actually produces them. 👉 share.google/fZeOdW12MRw42bs…

Astronomers using @almaobs in Chile have detected emission from neutral oxygen in four galaxies seen as they were roughly 700 to 800 million years after the Big Bang. The observations provide a more direct way to investigate the neutral gas associated with early star formation, helping researchers understand the conditions that allowed young galaxies to grow. Stars form when gas cools and gathers into sufficiently dense regions for gravity to drive collapse. Studying that material in distant galaxies is difficult, and different kinds of gas can contribute to the same observed signal. Neutral gas contains atoms that retain their electrons, whereas ionized gas has had electrons removed, often by radiation from young stars. The team measured an emission line produced by neutral oxygen at a rest wavelength of 145 micrometres. This gives researchers a specific tracer of neutral regions. They also searched for emission from ionized nitrogen to assess how much of the previously detected carbon emission could come from ionized material. Their analysis indicates that most of the carbon signal in these galaxies originates in neutral gas, strengthening its usefulness for investigating their star-forming reservoirs. By comparing the oxygen and carbon measurements with infrared emission and physical models, the researchers inferred dense gas exposed to ultraviolet radiation. The estimated densities resemble those found in galaxies undergoing intense bursts of star formation, although the ultraviolet radiation fields are weaker than in those starburst systems. These young galaxies therefore appear to contain substantial concentrations of dense material without reproducing all the conditions of the most extreme star-forming environments. What I find particularly useful is that this result can improve the interpretation of observations we already have. Carbon emission has been measured in many distant galaxies, and establishing where that emission comes from makes it easier to connect those measurements to the material available for forming stars. The sample contains only four galaxies, so larger surveys will be needed to establish how widespread these conditions were during the Universe’s first billion years. 👉 share.google/fQAoLyS9tf9PZgH…

. @ESA_Euclid first public survey data are revealing how the structure of galactic discs changes over cosmic time. A new study examines how brightness falls from the inner regions of a galaxy towards its outskirts, and how changes in that pattern can help us understand the way galaxies grow. A galactic disc is the flattened component containing stars, gas and dust, where spiral arms are often found. Its brightness usually decreases outwards, but that decline doesn’t always follow a single smooth profile. In some galaxies, it becomes steeper beyond a particular radius. In others, it becomes shallower, leaving a more extended outer component. Astronomers call these transitions “disc breaks”. They aren’t physical cracks or gaps. The team developed an automated analysis of 8,748 disc galaxies from Euclid’s Quick Data Release 1, reaching a redshift of about one. They then used a subset of 4,385 galaxies with reliable classifications to investigate how the different profiles vary with cosmic epoch. Among nearby galaxies, profiles that steepen towards the outskirts account for around half the sample. Looking further back in time, profiles with a shallower outer decline and those combining different kinds of breaks become more common, each reaching approximately 30% at a redshift close to one. The authors interpret this evolution as evidence that the processes shaping discs change as galaxies mature. Environmental influences may play a greater role earlier on, while gradual internal evolution becomes increasingly important later. However, the brightness profiles don’t uniquely identify the mechanisms responsible, and comparing galaxies at different distances doesn’t mean following the same individual galaxies through their lives. IMO, the most interesting aspect is Euclid’s ability to turn detailed measurements of galactic outskirts into a large statistical study. The limitation is that automated classification remains imperfect, with an estimated accuracy of around 70%. The paper acceptance hasn’t been confirmed. 👉 arxiv.org/html/2609.26877v1

The fourth dimension. #HisVoice 😍

Observations with the #JWST suggest that Chariklo’s two narrow rings may be changing over just a few years. An international team compared Webb measurements from October 2022 with earlier observations and found opposite differences: the inner ring blocked more starlight, while the outer ring produced a much weaker signal. The findings, raise questions about how these rings maintain their structure and whether their material is being replenished, redistributed or lost. Chariklo is a small body roughly 250 kilometres across that orbits the Sun between Saturn and Uranus. It belongs to a population called centaurs, which travel among the giant planets. Its rings are bands of separate particles orbiting around it, broadly like Saturn’s rings on a much smaller scale. They are not solid hoops: each particle moves around Chariklo under gravity, and together the particles form two narrow bands. Discovered in 2013, the rings are only a few kilometres wide and lie approximately 390 and 405 kilometres from Chariklo’s centre. Even Webb cannot directly photograph the detailed structure of these thin, distant rings. Instead, we observe what happens when they pass in front of a background star. As each ring crosses the line of sight, it briefly blocks some of the star’s light. By measuring how much the star dims and how long the dip lasts, researchers can work out properties of the material passing in front of it. This technique, called a stellar occultation, allows them to study structures that would otherwise be too small to distinguish. The measurements showed that the rings remained at essentially the same distances from Chariklo, but their opacity had changed. Compared with observations from 2017, the inner ring, C1R, appeared about 50% more opaque, while the outer ring, C2R, appeared about 60% less opaque. In practical terms, the inner ring was more effective at blocking the background star’s light, and the outer ring was less effective. Those percentages do not mean that the rings gained or lost the same proportion of their mass. How much light a ring blocks also depends on the sizes and arrangement of its particles and the wavelength being observed. Several processes could explain the differences. Additional material could have entered the inner ring, or its existing particles could have become rearranged. Collisions that break larger particles into smaller grains could also change its opacity without requiring a comparable increase in total mass. The weaker outer-ring signal might indicate that material is being lost, raising the possibility that this ring is temporary or needs occasional replenishment to survive. The observations do not yet identify which explanation is correct. There is also a complication in comparing the observations: Webb measured the rings in the near-infrared, whereas earlier measurements used different observing bands. The same collection of particles can block different amounts of light at different wavelengths. Some of the apparent changes could therefore reflect the way the rings were observed, alongside any physical evolution that occurred between observations. Further stellar occultations, particularly in visible light, will help separate these effects. They could establish whether Chariklo’s rings are changing over time and clarify how such a small body retains these narrow bands of orbiting material. 👉 share.google/VOdGjICSSLh8b4F…

Earth’s centre of mass changes position by several millimetres over the course of a year relative to the solid planet. Seasonal movements of water, snow and air alter how mass is distributed, shifting the point that represents the average position of all that mass. This geocentre provides the origin for global positioning systems, so even these small changes matter when scientists compare precise measurements of Earth’s surface. A new study, develops a more accurate way to estimate this seasonal motion. The measurement involves two reference points: the centre of mass of the entire Earth system, including its atmosphere and water, and the centre of figure defined by the solid surface. Their relative positions change as mass moves between regions. Satellites help locate the centre of mass through their response to Earth’s gravity. Ground stations track the two LAGEOS satellites by measuring the travel time of laser pulses reflected back to Earth. However, the stations themselves move when changing loads of water, snow and air deform the crust. Their uneven geographical distribution further complicates the measurement. The researchers corrected station positions for this elastic deformation and used both laser ranging and a combination of laser, GPS and low-orbit satellite observations. Their two estimates agree within 2.5 millimetres with the annual peak-to-peak oscillations estimated from the ITRF2020 reference frame and from GRACE-based analysis. The seasonal contributions have identifiable geographical patterns. According to NASA’s account, snow accumulation across North America and Eurasia reaches its maximum around March, contributing a displacement of about three millimetres towards the North Pole. Water storage in the Amazon basin peaks around April, with a contribution of approximately 2.2 millimetres towards South America. Later in the year, changing ocean mass shifts the centre towards the South Pacific. Atmospheric pressure patterns also contribute as air redistributes between regions. These movements overlap in three dimensions throughout the year. The revised seasonal motion is roughly half the size inferred in some earlier estimates. The improvement concerns how scientists measure and interpret the displacement; it does not establish that the physical motion has recently weakened. Separating the movement of the reference origin from actual changes at the surface helps scientists compare observations consistently. Satellite measurements of elevation and precise positioning depend on that distinction, particularly when the changes being studied are themselves small. 👉 nasa.gov/science-research/ea…

I wonder how many people have stopped to look at this Harvest Moon tonight, each carrying a different life into the same small moment of stillness. #Moon

Due to the immense scale of the universe, traditional methods like parallax become ineffective for measuring distances to faraway objects. We rely on a class of objects known as "standard candles" to overcome this limitation. These astrophysical objects, such as specific types of stars and supernovae, possess a known intrinsic luminosity—the amount of light they emit. By comparing the observed brightness of a standard candle with its known intrinsic luminosity, astronomers can determine its distance from Earth. This technique is fundamental for mapping the large-scale structure of the universe and understanding its expansion. Imagine standing in a large field at night, surrounded by identical lamps scattered at various distances. Closer lamps appear brighter, while those further away seem dimmer. If you know that all lamps emit the same amount of light, you can calculate their distances based on their observed brightness. This analogy illustrates how standard candles work in astronomy. By knowing the true luminosity of these objects, we can deduce their distances from their observed brightness. Types of Standard Candles. Cepheid Variable Stars. Characteristics: Cepheid variables are pulsating stars whose brightness varies in a regular pattern. The period of their pulsation is directly related to their intrinsic luminosity. Use: By measuring the pulsation period, astronomers can determine the star's luminosity and, consequently, its distance. This method was crucial in Edwin Hubble's discovery that our galaxy is just one among many in the expanding universe​. Type Ia Supernovae. Characteristics: These are thermonuclear explosions of white dwarf stars in binary systems. They have a consistent peak brightness, making them reliable standard candles. Use: Observing the peak brightness of Type Ia supernovae allows astronomers to measure distances to faraway galaxies, aiding in the study of the universe's expansion rate. While standard candles are essential tools, they are not without challenges. For example, recent studies have shown that Cepheid variables can lose mass through stellar winds, affecting their luminosity and complicating distance calculations. Observations from NASA's Spitzer Space Telescope have provided direct evidence of mass loss in Cepheids, prompting more precise measurements to maintain the accuracy of the cosmic distance ladder​. Standard candles are fundamental in cosmology, providing a means to measure vast cosmic distances and understand the universe's structure. They enable the construction of the cosmic distance ladder, which is crucial for mapping the universe and studying phenomena such as dark energy and the expansion rate of the universe.

A particle accelerator could, in principle, produce axions from the quantum vacuum. These hypothetical particles are among the possible constituents of dark matter, and a theoretical study describes a mechanism through which accelerated atomic nuclei could create them in pairs. Whether those pairs could actually be detected remains an unresolved experimental challenge. The calculation rests on how nuclear matter would affect an axion field. Within the framework the authors examine, an axion’s effective mass decreases inside a nucleus. Accelerating that nucleus changes the conditions experienced by the field and can generate particles through a process analogous to the dynamical Casimir effect. The researchers consider close encounters in which nuclei pass each other without directly overlapping, while their electromagnetic interaction deflects their trajectories. Their calculations predict that the emitted axions would be quantum entangled. The expression “from empty space” needs some care. In quantum field theory, a vacuum is the lowest energy state of fields, which retain quantum fluctuations even when no particles are present. Producing particles requires an energy supply: in this scenario, that energy would come from the accelerated nuclei. Energy conservation still applies. There’s also a distinction between discovering an axion and establishing what makes up cosmic dark matter. A laboratory detection would allow physicists to investigate the particle’s properties. Connecting it to the matter inferred from astronomical observations would require further evidence that it survives long enough and was produced in sufficient abundance during cosmic history. For now, the work provides a theoretical production mechanism whose practical detectability still needs investigation. 👉 share.google/BodTvkifFQvsrjb…

The Moon doesn’t generate a global magnetic field today, but some of its rocks remain magnetised. Explaining how they acquired that magnetisation has proved difficult: lunar samples give conflicting results, and both an ancient core dynamo and brief magnetic fields associated with impacts have been proposed. Research on the Dewar region, on the Moon’s far side, now supports the existence of a dynamo about 4.2 billion years ago. A team of astronomers combined gravity measurements from NASA’s GRAIL mission with magnetic models based on Lunar Prospector and Kaguya observations. At Dewar, unusually strong magnetic and gravity signals overlap. Their joint analysis indicates a buried body roughly 60 kilometres wide, reaching about 9 kilometres below the surface. Its density, magnetisation and geological setting are consistent with an ancient accumulation of solidified magma. Magnetic minerals can retain magnetisation acquired as a rock cools in an external field. Using estimates of the material’s magnetic properties, the researchers calculated that Dewar’s rocks required an ancient field exceeding 11 microtesla. Deposits from later impacts constrain the structure’s age to around 4.2 billion years. Together, these results support an internally generated field at that time, although they don’t establish how long the dynamo operated. The analysis also helps explain the bright, curved markings known as lunar swirls. At Dewar, horizontal magnetisation and surface material enriched in iron oxide could account for the contrast: the local field deflects solar wind particles, reducing the alteration that darkens exposed soil. The composition of the surface therefore matters alongside the magnetic field. The team favour a core dynamo over an impact origin for Dewar’s magnetisation. How the Moon’s small core sustained such a strong field remains unresolved. Measurements and samples from this region would help test the geological interpretation and the inferred field strength. 👉 share.google/tiPo1uU7HrWR4Lz…

A new theoretical study suggests that primordial black holes could provide an unexpected way to probe whether our Universe contains a hidden extra spatial dimension. The idea comes from the so-called Dark Dimension Scenario, a framework motivated by quantum-gravity arguments in which the familiar four-dimensional spacetime is embedded in a larger five-dimensional structure. Ordinary Standard Model particles would remain confined to our four-dimensional “brane”, while gravity could propagate into an additional compact spatial dimension roughly on the micron scale. Primordial black holes, or PBHs, are hypothetical black holes that may have formed during the first moments after the Big Bang, rather than from the collapse of massive stars. Because they could be extremely small, their gravitational fields might probe distances at which the extra dimension becomes physically relevant. Scientists examined several established mechanisms proposed for producing PBHs in the early Universe, including inflationary density fluctuations, cosmological phase transitions and the collapse of cosmic-string loops. Their analysis finds that, within the Dark Dimension Scenario and in the absence of exotic new low-energy physics, viable primordial black holes would inevitably become five-dimensional objects. The distinction depends on the relationship between the black hole’s horizon and the size of the extra dimension. When the horizon is much larger than the compact dimension, the black hole behaves essentially as an ordinary four-dimensional object. But sufficiently small black holes can gravitationally access the extra spatial direction, changing their geometry and physical properties. For PBHs produced during early-Universe phase transitions, the researchers argue that configurations that initially resemble four-dimensional black holes would become unstable and undergo a Gregory-Laflamme-type transition into five-dimensional objects. This instability is familiar from higher-dimensional gravity, where extended black objects can become unstable when their geometry reaches certain scales. For primordial black holes produced by collapsing cosmic strings, the situation is even more direct: under the assumptions of the model, they would form as five-dimensional black holes from the beginning. The extra dimension would also substantially modify Hawking evaporation. In standard four-dimensional physics, sufficiently small black holes lose energy rapidly through Hawking radiation and eventually disappear. Five-dimensional black holes of comparable mass behave differently: their temperature, horizon size and evaporation rate are modified, allowing some of them to survive much longer. The calculations suggest that PBHs produced from cosmic strings could, under certain conditions, have lifetimes comparable to the approximately 13.8-billion-year age of the Universe. If such objects were created in the early cosmos, some might therefore still exist today or could only now be reaching the final stages of evaporation. The authors also discuss a particularly speculative observational possibility involving the extremely energetic neutrino detected by the KM3NeT observatory. In the five-dimensional scenario, an evaporating primordial black hole could potentially emit particles into the higher-dimensional bulk. Those particles might subsequently produce a neutrino detectable on our brane, potentially offering an explanation for why such a high-energy neutrino could appear without an obvious accompanying high-energy photon signal. The connection is intriguing because the observed neutrino energy is close to the characteristic five-dimensional Planck scale predicted in this framework, but it remains a hypothesis rather than evidence for either primordial black holes or an extra dimension. The significance of the work is therefore not that a fifth dimension has been discovered, but that it identifies possible physical consequences if such a dimension exists. Primordial black holes would then behave very differently from their conventional four-dimensional counterparts, affecting their formation, stability, evaporation and possible observational signatures. Detecting those signatures could provide an indirect test of the dimensional structure of spacetime at scales that cannot currently be explored in laboratory experiments. For now, however, both primordial black holes and the dark dimension remain hypothetical, making this an interesting bridge between quantum-gravity theory, early-Universe cosmology and potentially observable astrophysics. 👉 journals.aps.org/prd/accepte…

The Sun may look constant from Earth, but magnetically it is anything but stable. Its activity rises and falls through an approximately 11-year solar cycle, moving between relatively quiet periods and active phases filled with sunspots, solar flares and other manifestations of a disturbed magnetic field. Although we have monitored these cycles for centuries, predicting the timing and strength of the next solar maximum remains difficult, which matters because strong solar activity can disrupt satellites, communications, navigation systems and electrical infrastructure. A new study suggests that an important clue may appear not when the Sun is becoming more active, but when it is becoming quiet. By examining previous solar cycles, they found that the decline from solar maximum does not always proceed smoothly. Instead, there appears to be a relatively abrupt “switch-off” point when sunspot numbers fall sharply. More importantly, the number of sunspots present around this transition correlates with the strength of the following solar maximum. In other words, the way one cycle shuts down may contain information about how energetic the next one will become. There is also a weaker relationship between the overall amplitudes of consecutive solar maxima, but the declining-phase indicator appears potentially more useful as a forecasting tool. The Sun is currently in Solar Cycle 25, which began in 2019 and has now passed its maximum, with activity expected to continue decreasing toward solar minimum around 2030. Based on the behaviour observed so far, analysis suggests that Solar Cycle 26 could be somewhat weaker than Cycle 25, although this is still an early prediction. A more decisive test should come around 2028, when the expected switch-off point can be measured and used to make a firmer forecast of the next cycle. Ultimately, the model will not be fully tested until Cycle 26 reaches its maximum in the mid-to-late 2030s. If the relationship holds, studying how the Sun enters its quiet phase could give us a valuable new way of anticipating its future magnetic activity and improving long-term space-weather forecasts. 👉 share.google/g1kmNBVLrjhW0TE…