"That's the Pinwheel galaxy," I said. The name is derived from its shape - albeit this pinwheel contains about a trillion stars.

The light from the Pinwheel traveled for 25 million years across the universe - about 150 quintillion miles - to get to my telescope.

My wife wondered: "Doesn't light get tired during such a long journey?"

Her curiosity triggered a thought-provoking conversation about light. Ultimately, why doesn't light wear out and lose energy over time?

Let's talk about light

Light is electromagnetic radiation: basically, an electric wave and a magnetic wave coupled together and traveling through space-time. It has no mass. That point is critical because the mass of an object, whether a speck of dust or a spaceship, limits the top speed it can travel through space.

But because light is massless, it's able to reach the maximum speed limit in a vacuum - about 186,000 miles (300,000 kilometers) per second, or almost 6 trillion miles per year (9.6 trillion kilometers). Nothing traveling through space is faster. To put that into perspective: In the time it takes you to blink your eyes, a particle of light travels around the circumference of the Earth more than twice.

As incredibly fast as that is, space is incredibly spread out. Light from the Sun, which is 93 million miles (about 150 million kilometers) from Earth, takes just over eight minutes to reach us. In other words, the sunlight you see is eight minutes old.

Alpha Centauri, the nearest star to us after the Sun, is 26 trillion miles away (about 41 trillion kilometers). So by the time you see it in the night sky, its light is just over four years old. Or, as astronomers say, it's four light years away.

With those enormous distances in mind, consider Cristina's question: How can light travel across the universe and not slowly lose energy?

Actually, some light does lose energy. This happens when it bounces off something, such as interstellar dust, and is scattered about.

But most light just goes and goes, without colliding with anything. This is almost always the case because space is mostly empty - nothingness. So there's nothing in the way.

When light travels unimpeded, it loses no energy. It can maintain that 186,000-mile-per-second speed forever.

It's about time

That's an example of time dilation - time moving at different speeds under different conditions. If you're moving really fast, or close to a large gravitational field, your clock will tick more slowly than someone moving slower than you, or who is further from a large gravitational field. To say it succinctly, time is relative. Now consider that light is inextricably connected to time. Picture sitting on a photon, a fundamental particle of light; here, you'd experience maximum time dilation. Everyone on Earth would clock you at the speed of light, but from your reference frame, time would completely stop.

That's because the "clocks" measuring time are in two different places going vastly different speeds: the photon moving at the speed of light, and the comparatively slowpoke speed of Earth going around the Sun.

What's more, when you're traveling at or close to the speed of light, the distance between where you are and where you're going gets shorter. That is, space itself becomes more compact in the direction of motion - so the faster you can go, the shorter your journey has to be. In other words, for the photon, space gets squished.

Which brings us back to my picture of the Pinwheel galaxy. From the photon's perspective, a star within the galaxy emitted it, and then a single pixel in my backyard camera absorbed it, at exactly the same time. Because space is squished, to the photon the journey was infinitely fast and infinitely short, a tiny fraction of a second.

But from our perspective on Earth, the photon left the galaxy 25 million years ago and traveled 25 million light years across space until it landed on my tablet in my backyard.

And there, on a cool spring night, its stunning image inspired a delightful conversation between a nerdy scientist and his curious wife.

]]> Fri, 23 MAY 2025 02:09:34 AEST Osaka,Japan (SPX) May 22, 2025 - Lightning has long captivated scientists, but a new study from The University of Osaka has shed unprecedented light on the high-energy physics behind it. Researchers have captured the first-ever detailed observation of a terrestrial gamma-ray flash (TGF) occurring precisely in sync with a lightning discharge.

TGFs are extremely brief but intense bursts of gamma rays, lasting mere microseconds, and are generally difficult to detect. The study, soon to appear in Science Advances, presents a landmark finding by using a cutting-edge multi-sensor system that tracked optical signals, radio waves, and high-energy radiation during a storm over Kanazawa City in Ishikawa Prefecture.

Two lightning leaders-one descending from a thundercloud and another ascending from a transmission tower-were observed approaching each other. A powerful TGF was emitted 31 microseconds before the lightning paths collided, and radiation continued for 20 microseconds after the contact, which produced a -56 kA discharge.

"The ability to study extreme processes such as TGFs originating in lightning allows us to better understand the high-energy processes occurring in Earth's atmosphere," said lead author Yuuki Wada.

This observation confirms theories that TGFs are caused by electrons accelerated to relativistic speeds in strong electric fields formed during lightning events. It also aligns with models involving thermal runaway and relativistic feedback mechanisms.

Senior author Harufumi Tsuchiya emphasized the novelty of the method, stating, "The multi-sensor observations performed here are a world-first; although some mysteries remain, this technique has brought us closer to understanding the mechanism of these fascinating radiation bursts."

Beyond scientific curiosity, the findings hold practical implications for enhancing the protection of infrastructure against the energetic effects of lightning.

Research Report:Downward Terrestrial Gamma-ray Flash Associated with Collision of Lightning Leaders

]]> Fri, 23 MAY 2025 02:09:34 AEST Berlin, Germany (SPX) May 22, 2025 - Astronomers have captured a rare cosmic encounter in which a galaxy armed with a powerful quasar bombards a companion, drastically altering its ability to form stars. The discovery, detailed in Nature, showcases a previously unseen phenomenon of quasar radiation interfering with galactic star formation.

Using data from the European Southern Observatory's Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA), researchers observed two galaxies locked in a gravitational skirmish. The pair repeatedly rush toward each other at about 500 km/s, exchanging glancing blows before recoiling for another charge. "We hence call this system the 'cosmic joust'," said Pasquier Noterdaeme of the Institut d'Astrophysique de Paris and the French-Chilean Laboratory for Astronomy.

In this dramatic intergalactic duel, one galaxy holds an advantage-a blazing quasar at its core. Quasars, which are the luminous centers of some galaxies powered by supermassive black holes, release torrents of energy. That energy, the researchers found, is lancing through the other galaxy, stripping away its potential for new stars by disrupting its internal gas structure.

"This is the first time we've directly observed the effect of a quasar's radiation on the inner gas of a regular galaxy," noted Sergei Balashev of the Ioffe Institute in St Petersburg. The radiation leaves behind only compact, dense gas clouds-insufficient for large-scale star formation.

The encounter also benefits the quasar's host galaxy. As Balashev explained, galaxy mergers can funnel massive amounts of gas toward central black holes, intensifying quasar activity and reinforcing the destructive radiation assault.

The team relied on ALMA's precision to distinguish the two galaxies, previously indistinguishable as a single object. ESO's X-shooter instrument then enabled them to dissect the quasar's light as it passed through the injured galaxy, revealing how deeply the radiation affected the gas composition.

Future studies with next-generation observatories like ESO's Extremely Large Telescope could expand on these findings. "It will certainly allow us to push forward a deeper study of this, and other systems," said Noterdaeme, "to better understand the evolution of quasars and their effect on host and nearby galaxies."

Research Report:Quasar radiation transforms the gas in a merging companion galaxy

]]> Fri, 23 MAY 2025 02:09:34 AEST Columbus OH (SPX) May 12, 2025 - Magnetar flares, colossal cosmic explosions, may be directly responsible for the creation and distribution of heavy elements across the universe, suggests a new study.

For decades, astronomers only had theories about where some of the heaviest elements in nature, like gold, uranium and platinum, come from. But by taking a fresh look at old archival data, researchers now estimate that up to 10% of these heavy elements in the Milky Way are derived from the ejections of highly magnetized neutron stars, called magnetars.

Until recently, astronomers had unwittingly overlooked the role that magnetars, essentially dead remnants of supernovae, might play in early galaxy formation, said Todd Thompson, co-author of the study and a professor of astronomy at The Ohio State University.

"Neutron stars are very exotic, very dense objects that are famous for having really big, very strong magnetic fields," said Thompson. "They're close to being black holes, but are not."

While the origins of heavy elements had long been a quiet mystery, scientists knew that they could only form in special conditions through a method called the r-process (or rapid-neutron capture process), a set of unique and complex nuclear reactions, said Thompson.

Scientists saw this process in action when they detected the collision of two super-dense neutron stars in 2017. This event, captured using NASA telescopes, the Laser Interferometer Gravitational wave Observatory (LIGO) and other instruments, provided the first direct evidence that heavy metals were being created by celestial forces.

But further evidence showed that other mechanisms might be needed to account for all these elements, as neutron star collisions might not produce heavy elements fast enough in the early universe. According to this new study, building on these clues helped Thompson and his collaborators recognize that powerful magnetar flares could indeed serve as a potential ejectors of heavy elements, a finding confirmed by 20-year-old observations of SGR 1806-20, a magnetar flare so bright that some measurements of the event could only be made by studying its reflection off the moon.

By analyzing this magnetar flare event, researchers determined that the radioactive decay of the newly created elements matched up with their theoretical predictions about the timing and types of energies released by a magnetar flare after it ejected heavy r-process elements. The researchers also theorized that magnetar flares produce heavy cosmic rays, extremely high-velocity particles whose physical origin remains unknown.

"I love new ideas about how systems work, how new discoveries work, how the universe works," Thompson said. "That's why results like this are really exciting."

The study was recently published in The Astrophysical Journal Letters.

Magnetars may provide unique insights into galactic chemical evolution, including the formation of exoplanetary systems and their habitability.

Not only do magnetars produce valuable metals like gold and silver that end up on Earth, the supernova explosions that cause them also produce elements like oxygen, carbon and iron that are vital for many other, more complex celestial processes.

"All of that material they eject gets mixed into the next generation of planets and stars," said Thompson. "Billions of years later, those atoms are incorporated into what could potentially amount to life."

Altogether, these findings have deep implications for astrophysics, particularly for scientists studying the origin of both heavy elements and fast radio bursts - brief shivers of electromagnetic radio waves from faraway galaxies. Understanding how matter ejects from magnetars could help scientists learn more about them.

Due to their rarity and short duration, magnetar flares can be difficult to observe,

and current space-based telescopes like the James Webb Space Telescope and Hubble don't have the dedicated abilities needed to detect and study their emission signals. Even more specialized observatories like NASA's Fermi Gamma-ray Space Telescope can only see the brightest part of gamma-ray flashes from nearby galaxies.

Instead, one proposed NASA mission, the Compton Spectrometer and Imager (COSI), could bolster the team's work by surveying the Milky Way for energetic events like giant magnetar flares. Though another event like SGR 1806-20 might not occur this century, if a magnetar flare did detonate in our backyard, COSI could be used to better identify the individual elements created from its eruption and allow this team of researchers to confirm their theory about where heavy elements in the universe come from.

"We're generating a bunch of new ideas about this field, and ongoing observations will lead to even more great connections," said Thompson.

Research Report:Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from the SGR 1806-20 Magnetar Giant Flare

]]> Fri, 23 MAY 2025 02:09:34 AEST Los Angeles CA (SPX) May 15, 2025 - A new theory from Dartmouth College researchers suggests that dark matter, the elusive substance making up most of the universe's mass, may have originated from the rapid transformation of fast-moving, nearly massless particles in the early universe.

Published in Physical Review Letters, the study posits that dark matter formed when these particles, initially moving at relativistic speeds, lost energy and gained mass after pairing up. This model departs from conventional views by proposing that dark matter began as high-energy particles that cooled dramatically, taking on mass as they slowed.

"Dark matter started its life as near-massless relativistic particles, almost like light," said Robert Caldwell, professor of physics and astronomy at Dartmouth and the study's senior author. "That's totally antithetical to what dark matter is thought to be-it is cold lumps that give galaxies their mass. Our theory tries to explain how it went from being light to being lumps."

This process, the researchers argue, could have left a detectable imprint on the Cosmic Microwave Background (CMB), the radiation left over from the Big Bang. Unlike conventional theories that view dark matter as inherently massive, this approach envisions it forming through a rapid phase change as particles cooled.

According to Caldwell and his co-author, Dartmouth senior Guanming Liang, these early particles bonded due to the opposing directions of their spin, similar to the magnetic alignment of the north and south poles. As the universe cooled, this spin imbalance caused a sudden energy drop, leading to the formation of the cold, heavy particles thought to constitute dark matter today.

"The most unexpected part of our mathematical model was the energy plummet that bridges the high-density energy and the lumpy low energy," Liang said. "At that stage, it's like these pairs were getting ready to become dark matter."

The researchers draw parallels to superconductivity, where massless particles can form Cooper pairs that conduct electricity without resistance. This mechanism, they suggest, supports the plausibility of dark matter formation through a similar transition.

Liang added, "The mathematical model of our theory is really beautiful because it's rather simplistic-you don't need to build a lot of things into the system for it to work. It builds on concepts and timelines we know exist."

Caldwell and Liang believe that ongoing and future CMB studies, including those by the Simons Observatory and CMB Stage 4, could provide the data needed to test their hypothesis.

"It's exciting," Caldwell said. "We're presenting a new approach to thinking about and possibly identifying dark matter."

Research Report:Cold Dark Matter Based on an Analogy With Superconductivity

]]> Fri, 23 MAY 2025 02:09:34 AEST Storrs CT (SPX) May 21, 2025 - Earth - our tiny blue dot in the galaxy - is approximately 26,000 light years away from a fascinating and active region of the Milky Way called the Central Molecular Zone (CMZ). This region holds clues about how stars are born, how energy moves through our galaxy, and maybe even some details about dark matter.

However, analyzing this area is challenging, because we do not have a clear top-down view of the Milky Way. UConn's Milky Way Laboratory, headed by the Department of Physics Associate Professor Cara Battersby, present their comprehensive analysis and 3-dimensional top-down model of the CMZ in a series of four papers in the Astrophysical Journal.

The CMZ is a region of extremes and complexity, but it is also the only CMZ we can study in detail.

"We like to call the CMZ the way station of the galaxy: between gas that's flowing in from the disc of the galaxy along dust lanes into the CMZ," Battersby says. "That gas either remains in the CMZ and orbits around the center of the galaxy, where it sometimes forms stars, or it can travel onwards to the supermassive black hole at the center of the galaxy."

One question Battersby is interested in learning more about is when the Milky Way's supermassive black hole, called Sagittarius A, "feeds" or actively accretes material. As a galactic way station, the CMZ controls when and if those materials travel to the black hole. Making direct observations to answer this question is tricky because the CMZ is home to lots of gas, dust, and stars, along with the fact that we are very far away and can only see it from the side.

"To understand how our own CMZ regulates this gas inflow, we need a top-down picture," Battersby says. "We probably have hundreds of thousands of images of our galactic center, all in this sideways perspective. We can learn everything we want about these clouds, but if you don't know which ones are flowing toward the black hole or which ones are orbiting, then you can't really say anything about how the CMZ regulates this gas flow. We can do a better job of modeling the three-dimensional gas distribution."

In this series of papers, Battersby's research group takes all available evidence to measure and catalog aspects of the clouds in this region of the galaxy to create the best possible top-down three-dimensional view of the CMZ.

The first step was to compile a comprehensive catalog of structures in the CMZ and to measure their physical and kinematic properties, such as mass, radii, temperature, and velocity dispersion, described in papers one and two.

With these comprehensive catalogs, the next two papers focus on the small-scale structures within the catalog, which are thought to be individual molecular clouds that may be the birthplaces of clusters of stars, says Battersby. The third paper was led by former post-doctoral fellow Daniel Walker and the fourth paper was led by current Ph.D. student Dani Lipman.

The galactic center is very bright and emits light at many wavelengths, therefore, the properties of the molecular clouds give clues about their location within it. The researchers used different approaches to measure and determine which clouds are in front of or behind the galactic center.

"These molecular clouds are places where stars form only when the gas is very dense and very cold, and much of the gas in the galactic center is hot and diffuse," Battersby says. "These cocoons of cool, dense gas mean that when they're in front of the galactic center, they absorb the bright light from the galactic center, and they look like shadows. On the other hand, if those clouds are behind the galactic center, then this light passes through, and the clouds don't block that light at all."

The researchers developed new techniques to measure how much light is blocked by the molecular clouds with the assumption that if a lot of light is blocked, it is likely that the cloud is in front of the galactic center.

"Papers three and four use two different techniques. Paper three focuses on radio wavelengths of light, and it focuses on the molecular clouds absorbing the radio wavelengths. Paper four focuses on infrared dust extinction and details a careful technique to measure the "shadow" based on the properties of the cloud, thereby quantifying the likelihood that it's either in front of or behind the Galactic Center," says Battersby.

Next, the researchers modeled what their data suggested was happening in the CMZ and compared that to existing models of what the galactic center may look like from the top down.

There were three predominant models of what our galactic center may look like, and Battersby says the locations of the molecular clouds the group mapped vary quite a bit across the different existing models. By accounting for the dynamic movements of various clouds, the researchers found existing models lacked this complexity and more work is needed to study the flow of gas in the CMZ.

"Paper three presented a new simple ellipse model that is a slightly better fit than the previous models. Dani Lipman is currently drafting paper five that presents a quantitative best-fit model of the top-down view of our Galaxy's CMZ, which includes the release of public code so future researchers can continue to improve our top-down model of the CMZ as new data arrives."

Lipman says that paper five aims to combine any available data to determine the most likely position of a given cloud in front of or behind Sagittarius A*. These positions are then used to find a best fitting top-down model for the CMZ. The model is continually updated and improved as more data becomes available,

"Modern science is wonderfully collaborative, so releasing our code is a huge part of engaging in the community and offering resources to new scientists and students who are eager to join in answering these questions," says Lipman.

This series of papers is a major step forward in understanding the 3-D structure of our Galaxy's CMZ and enables researchers, like Battersby's Milky Way Lab, to start answering pressing questions about our galaxy,

"The CMZ provides 'close' access to extreme phenomena seen throughout the Universe, such as an accreting supermassive black hole, and star formation in a highly turbulent environment," says Battersby. "Knowing the 3-D structure is essential to tracing flows towards the black hole as well as testing theories of star formation in an extreme environment, because you need to know where everything is in this dynamic environment."

Research Report:3D CMZ. I. Central Molecular Zone Overview

]]> Fri, 23 MAY 2025 02:09:34 AEST Sydney, Australia (SPX) May 21, 2025 - Researchers at the International Centre for Radio Astronomy Research (ICRAR) have discovered that the spatial concentration of gas within galaxies plays a more critical role in star formation than the overall volume of gas present.

The study, led by PhD candidate Seona Lee from The University of Western Australia's ICRAR node, utilized data from around 1,000 galaxies mapped by CSIRO's ASKAP radio telescope, part of the WALLABY survey. This effort marks a major advancement over prior surveys that assessed gas distribution in only a few hundred galaxies.

The findings reveal that galaxies forming stars typically exhibit denser accumulations of atomic hydrogen gas in their stellar regions, rather than simply possessing large total gas reserves.

"It was very exciting to see a correlation between star formation and where the atomic hydrogen gas is located," said Lee.

ASKAP's high-resolution capabilities enabled the team to precisely determine both the location and density of this atomic gas across an unprecedented number of galaxies.

Professor Barbara Catinella, ICRAR Senior Principal Research Fellow and co-leader of the WALLABY survey, emphasized the significance of gas distribution using a culinary analogy. "While different cakes require different amounts of flour, to bake a cake properly, you focus on the flour that's in the bowl, not the unused flour left in the package," she said.

Understanding where the gas is dense enough to support star formation, rather than assessing the total galactic gas, is central to determining how stars are born and how galaxies evolve. The team examined both radio wave and optical data to evaluate gas levels in star-forming regions.

"To learn about how stars are formed, we had to measure the atomic hydrogen gas in areas where stars are actively coming to life," Lee added. "This is important for figuring out just how much gas is really supporting the creation of new stars."

Research Report:WALLABY - The ASKAP HI All-Sky Survey

]]> Fri, 23 MAY 2025 02:09:34 AEST Berlin, Germany (SPX) May 19, 2025 - Astronomers have uncovered a vast population of protoplanetary disk candidates within the Central Molecular Zone (CMZ) near the Milky Way's core, a region known for its extreme conditions that differ significantly from those in the more studied areas of our galaxy. These findings come from a comprehensive survey conducted by an international research team from the Kavli Institute for Astronomy and Astrophysics at Peking University (KIAA, PKU), the Shanghai Astronomical Observatory (SHAO), and the Institute of Astrophysics at the University of Cologne (UoC), among others.

The team performed the most sensitive and complete survey to date of three major molecular clouds within the CMZ, revealing more than five hundred dense cores - the birthplaces of new stars. These results were achieved using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which combines signals from multiple antennas to achieve the high resolution needed to penetrate the thick dust surrounding these distant regions. "This allows us to resolve structures as small as a thousand astronomical units even at CMZ distances of roughly 17 billion AU away," explained Professor Xing Lu from the Shanghai Astronomical Observatory, the lead scientist on the ALMA project.

The researchers used a 'dual-band' technique to observe these clouds at two distinct wavelengths simultaneously, providing crucial spectral data on their composition and structure. This approach revealed that over 70% of the dense cores were significantly redder than expected, a surprising result that challenges long-standing assumptions about the nature of these regions. "We were astonished to see these 'little red dots' cross the whole molecular clouds," said Fengwei Xu, the study's first author and a doctoral researcher at the University of Cologne.

Two primary explanations for this unexpected reddening have been proposed. The first suggests that these cores may contain smaller, optically thick structures, possibly protoplanetary disks, which absorb more light at shorter wavelengths. Alternatively, the researchers speculate that these regions might host millimetre-sized dust grains, much larger than the typical micron-sized particles found in less dense interstellar environments. "Our models indicate that some cores may contain millimetre-sized grains, which could only form in protoplanetary disks and then be expelled - perhaps by protostellar outflows," said Professor Hauyu Baobab Liu of the National Sun Yat-sen University, who led the radiative transfer modelling for the study.

Regardless of which scenario proves more accurate, both interpretations point to the widespread presence of protoplanetary disks within the CMZ. "It is exciting that we are detecting possible candidates for protoplanetary disks in the Galactic Centre," said Professor Peter Schilke, a co-supervisor of Fengwei Xu's research. "The conditions there are very different from our neighbourhood, offering a unique opportunity to study planet formation in an extreme environment."

Future observations using multi-band imaging techniques will be critical for refining our understanding of these distant, enigmatic systems, potentially providing new insights into the early stages of planetary formation.

Research Report:Dual-band Unified Exploration of three Central Molecular Zone Clouds (DUET). Cloud-wide census of continuum sources showing low spectral indices

]]> Fri, 23 MAY 2025 02:09:34 AEST Los Angeles CA (SPX) May 14, 2025 - An international team led by Princeton University researchers has conducted the most precise simulations of magnetized turbulence in the Galaxy to date, revealing surprising discrepancies with long-established theoretical models. These large-scale computations, leveraging the power of over 140,000 parallel processors at the Leibniz Supercomputing Centre, have captured the complex behavior of turbulence as it transfers energy across vast ranges of scales.

The findings indicate that magnetic fields significantly alter how turbulent energy cascades through the interstellar medium, suppressing small-scale motions while amplifying wave-like disturbances known as Alfven waves. This insight challenges the conventional understanding of how energy moves through the cosmos, with potential implications for space weather forecasting and the safety of future space missions.

James Beattie, the study's lead author and a postdoctoral researcher at Princeton's Department of Astrophysical Sciences, noted the scale of this computational feat, comparing it to running a simulation on a single laptop from the dawn of human civilization until today. "These simulations bring us a step closer to uncovering the true nature of astrophysical turbulence, potentially revealing universal features that span the entire Universe," he said.

Amitava Bhattacharjee, a co-author and professor at Princeton, emphasized the real-world importance of the work: "These findings not only deepen our understanding of cosmic turbulence but also have practical implications for the safety of astronauts and satellites, as well as the interpretation of data from NASA missions studying the plasma environments near Earth and beyond."

The new study, published in Nature Astronomy on May 13, 2025, includes contributions from researchers at the Australian National University, Heidelberg University, and the Leibniz Supercomputing Center.

Research Report:The spectrum of magnetized turbulence in the interstellar medium

]]> Fri, 23 MAY 2025 02:09:34 AEST Los Angeles CA (SPX) May 12, 2025 - Buried deep in the ice in the Antarctic are "eyes" that can see elementary particles called neutrinos, and what they've observed is puzzling scientists: a remarkably strong neutrino signal accompanied by a surprisingly weak gamma-ray emission in the galaxy NGC 1068, also known as the Squid Galaxy.

The "eyes" are a collection of detectors buried in a cubic kilometer of ice called the IceCube Neutrino Observatory. Theoretical physicists from UCLA, the University of Osaka, and the University of Tokyo Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) are using their observations of NGC 1068 to propose a completely new route by which neutrinos can be produced.

Neutrinos are subatomic particles that interact only very weakly with gravity and can pass through matter. This makes them even harder to detect than other particles, such as electrons. The IceCube Neutrino Observatory consists of 5,160 sensors buried in clear, compressed Antarctic ice that look for events that could be produced by neutrinos when they pass through the ice, interact with it and create charged particles.

"We have telescopes that use light to look at stars, but many of these astrophysical systems also emit neutrinos," said Alexander Kusenko, professor of physics and astronomy at UCLA and a senior fellow at Kavli IPMU. "To see neutrinos, we need a different type of telescope, and that's the telescope we have at the South Pole."

The IceCube neutrino telescope detected very energetic neutrinos coming from NGC 1068 accompanied by a weak gamma-ray flux, hinting that these neutrinos may have been produced in a different way than previously thought. The NGC 1068 data is perplexing because, typically, energetic neutrinos from active galactic centers are thought to originate from interactions between protons and photons, producing gamma rays of comparable intensity. Thus, energetic neutrinos are usually paired with energetic gamma rays.

NGC 1068's gamma-ray emission is significantly lower than expected and shows a distinctly different spectral shape. Traditional models, including those based on proton-photon collisions and emission from the galaxy's hot plasma region known as the "corona," have been widely used to explain such neutrino signals, but they have faced theoretical limitations, prompting the search for a new explanation.

In a new paper published in Physical Review Letters, Kusenko and colleagues suggest that the high-energy neutrinos from NGC 1068 primarily result from the decay of neutrons when helium nuclei in the galaxy's jet break apart under intense ultraviolet radiation. When these helium nuclei collide with ultraviolet photons emitted by the galaxy's central region, they fragment, releasing neutrons that subsequently decay into neutrinos. The energies of the resulting neutrinos match the observations.

Additionally, electrons generated by these nuclear decays interact with surrounding radiation fields, creating gamma rays consistent with the observed lower intensity. This scenario elegantly explains why the neutrino signal dramatically outshines the gamma-ray emission and accounts for the distinct energy spectrum observed in both neutrinos and gamma rays.

The breakthrough helps scientists understand how cosmic jets in active galaxies can emit powerful neutrinos without a corresponding gamma-ray glow, shedding new light on the extreme, complex conditions surrounding supermassive black holes, including the one at the center of our own galaxy.

"We don't know very much about the central, extreme region near the galactic center of NGC1068," said Kusenko. "If our scenario is confirmed, it tells us something about the environment near the supermassive black hole at the center of that galaxy."

The new paper proposes that if a helium nucleus accelerates in the jet of a supermassive black hole, it crashes into photons and breaks apart, spilling its two protons and two neutrons into space. The protons can fly away, but the neutrons are unstable and fall apart, or decay, into neutrinos without producing gamma rays.

"Hydrogen and helium are the two most common elements in space," said first author and UCLA doctoral student Koichiro Yasuda. "But hydrogen only has a proton, and if that proton runs into photons, it will produce both neutrinos and strong gamma rays. But neutrons have an additional way of forming neutrinos that don't produce gamma rays. So helium is the most likely origin of the neutrinos we observe from NGC 1068."

The work reveals the existence of hidden astrophysical neutrino sources, whose signals may previously have gone unnoticed due to their faint gamma-ray signatures.

"This idea offers a new perspective beyond traditional corona models. NGC 1068 is just one of many similar galaxies in the universe, and future neutrino detections from them will help test our theory and uncover the origin of these mysterious particles," said co-author and the University of Osaka professor of astrophysics Yoshiyuki Inoue.

Like NGC 1068, our galaxy also has a supermassive black hole at its center, where unfathomably immense gravity and energy literally tear atoms apart, and the neutrino discovery holds for our galaxy, too. Although there's not necessarily a straight line from understanding the galactic center to improvements in human welfare, knowledge gained through the study of particles like neutrinos and radiation like gamma rays has a tendency to lead technology down surprising and transformative paths.

"When J.J. Thompson received the 1906 Nobel Prize in physics for the discovery of electrons, he famously gave a toast at a dinner after the ceremony, saying that this was probably the most useless discovery in history," said Kusenko. "And, of course, every smartphone, every electronic device today, uses the discovery that Thompson made nearly 125 years ago."

Kusenko also said that particle physics gave birth to the World Wide Web, which originated as a network developed by physicists who needed to move large amounts of data between labs. He pointed out that the discovery of nuclear magnetic resonance seemed obscure at the time but led to the development of magnetic resonance imaging technology, which is now used routinely in medicine.

"We stand at the very beginning of the new field of neutrino astronomy, and the mysterious neutrinos from NGC 1068 are one of the puzzles we have to solve along the way," said Kusenko. "Investment in science is going to produce something that you may not be able to appreciate now but could produce something big decades later. It's a long-term investment, and private companies are reluctant to invest in the kind of research we're doing. That's why government funding for science is so important, and that's why universities are so important."

The research was funded by the Department of Energy, the World Premier International Research Center Initiative (WPI), and the Japan Society for the Promotion of Science.

]]> Fri, 23 MAY 2025 02:09:34 AEST Subscribe to our daily selection of space, military, environment and energy newsletters responseText http://visitor.constantcontact.com/manage/optin/ea?v=0016gbbKsaiGSpQFojVO8ZoHw%3D%3D