The knee in the cosmic ray spectrum has long been hypothesized as a signature of the limit to which conventional cosmic accelerators could energize particles, marking a transition from one power-law regime to another. Yet, definitive evidence connecting this feature to specific astrophysical sources remained elusive—until now. Published in leading journals National Science Review and Science Bulletin, two comprehensive studies led by an international consortium of researchers have identified micro-quasars powered by black hole accretion systems as the prime candidates behind this cosmic phenomenon. These compact high-energy sources operate within the Milky Way and produce particle acceleration previously underestimated in galactic models.

Micro-quasars are formed when black holes in binary star systems siphon material from their companions, triggering relativistic jets capable of accelerating particles to ultra-high energies. Utilizing the unparalleled sensitivity and hybrid detection capabilities of LHAASO, scientists achieved the first systematic observation of ultra-high-energy gamma rays emanating from five notable micro-quasars: SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070, and Cygnus X-1. These gamma emissions provide a direct window into the presence of PeV-energy protons and other cosmic particles energized by black hole jet systems.

Especially striking were the findings related to SS 433, where gamma radiation spatially coincides with a massive ambient atomic cloud. This overlap signifies that particles accelerated by the black hole are interacting with surrounding matter, thereby producing gamma rays via hadronic collisions. Intriguingly, the proton energies in SS 433 exceed 1 PeV, with an astounding power output on the order of 10^32 joules per second—energy comparable to the detonation of four trillion powerful hydrogen bombs every second. Similarly, V4641 Sgr exhibited gamma rays reaching 0.8 PeV, categorizing it as a super PeV particle accelerator with parent particles surpassing 10 PeV in energy.

These discoveries profoundly challenge the traditional paradigm that supernova remnants are the exclusive sources of galactic cosmic rays. While supernova remnants do contribute to cosmic ray acceleration, both observational data and theoretical models assert their incapacity to reach energies beyond the knee. The LHAASO observations reposition micro-quasars as vital agents capable of not only reaching but exceeding the knee threshold, thereby filling a critical gap in cosmic ray origin theories.

A major technical hurdle overcome by LHAASO was the precise measurement of the proton energy spectrum in the PeV region. Detecting cosmic ray protons at these extreme energies is inherently difficult due to their rarity and the interference introduced by the Earth’s atmosphere in ground-based observatories. Furthermore, satellite-based cosmic ray detectors possess limited collection areas, restricting their effectiveness at ultra-high energies. Through a novel multi-parameter measurement approach and rigorous statistical selection of a high-purity proton sample, LHAASO achieved precision rivaling satellite measurements, revealing a complex spectral structure characterized by an unanticipated high-energy component superimposed on existing power-law distributions.

Integrating LHAASO’s findings with those from space-borne experiments such as AMS-02 and DAMPE, scientists have recognized multiple, discrete acceleration sources within the Milky Way, each imprinting distinct spectral features on cosmic rays. This multiplex acceleration model elucidates the knee as the energy boundary of the most potent accelerators—in this case, black hole-driven micro-quasars—rather than a singular universal cutoff. This nuance significantly redefines the cosmic ray landscape and provides essential context for interpreting high-energy particle flux variations observed on Earth.

The enriched understanding emerging from these studies emphasizes that the cosmic ray proton flux in the PeV range is dominated by contributions from micro-quasars, with acceleration capabilities far surpassing those of supernova remnants. This hierarchical structuring implies that while supernova remnants provide the bulk of lower energy cosmic rays, micro-quasars furnish the extreme high-energy particles responsible for the knee, thereby offering a more comprehensive explanation compatible with observational spectra.

Together, the discoveries of micro-quasar gamma-ray emissions and the refined proton energy spectrum measurement combine into a compelling narrative that not only resolves the knee’s origin but also illuminates the role of black holes as astrophysical particle accelerators. This breakthrough provides a critical observational anchor for theoretical models that have long suggested relativistic jets as engines of extreme particle acceleration, cementing black hole systems as fundamental contributors to the high-energy cosmic environment.

LHAASO’s multidetector, hybrid array methodology, which simultaneously observes cosmic ray sources through ultra-high-energy gamma rays and performs localized cosmic ray particle measurements near Earth, represents a revolutionary approach. This dual capacity allows unprecedented cross-validation of acceleration processes and spectral signatures, linking distant astrophysical phenomena with terrestrial detection data. For the first time, observational evidence directly associates the knee structure with a distinct category of astrophysical accelerator—black hole jet systems—sharpening our ability to map cosmic origins.

Conceived, designed, and operated by Chinese scientists, LHAASO embodies cutting-edge technology in high-energy particle astrophysics. Its sensitivity to both gamma-ray astronomy and cosmic ray measurement has enabled a suite of globally impactful discoveries over recent years, pushing the frontiers of knowledge regarding extreme physical processes in the universe. With these latest contributions, LHAASO cements its position at the forefront of cosmic ray research, enabling deeper exploration into the mechanisms shaping the high-energy cosmos.

Moreover, the implications of this research extend beyond cosmic ray physics, touching fundamental questions about black hole accretion, jet formation, and particle acceleration mechanisms under extreme gravitational and magnetic fields. As micro-quasars now emerge as key astro-particle laboratories, further observations will refine particle acceleration models and potentially unravel connections between cosmic rays and other high-energy astrophysical phenomena such as neutrinos and gravitational waves.

This paradigm-shifting work underscores the power of international collaboration and state-of-the-art observatories in resolving astrophysical puzzles once considered intractable. As cosmic ray research progresses, the integration of multi-messenger astronomy and next-generation instrumentation will undoubtedly build upon the foundation established by LHAASO’s groundbreaking findings, ushering a new era of discovery in high-energy astrophysics.

Subject of Research: Cosmic ray origins and high-energy particle acceleration by micro-quasars

Article Title: [Not explicitly provided in the content]

News Publication Date: 16-Nov-2025

Web References: http://dx.doi.org/10.1016/j.scib.2025.10.048

Image Credits: LHAASO Collaboration

Keywords

Cosmic rays; Micro-quasars; Black hole accretion; Ultra-high-energy gamma rays; Particle acceleration; PeV cosmic rays; LHAASO observatory; Astroparticle physics; Galactic cosmic ray sources

Blazars are noteworthy mechanisms in the universe; they are characterized by their ability to produce narrow jets of matter that travel at nearly the speed of light toward Earth. These jets emit intense gamma radiation, observable by ground-based telescopes, extending to energies reaching several teraelectronvolts (TeV). As high-energy gamma rays traverse the vast expanse of intergalactic space, they scatter against the faint background light emitted by stars. This interaction generates cascades of electron–positron pairs that should, theoretically, produce lower-energy gamma rays detectable by advanced space observatories like the Fermi satellite. Despite extensive monitoring, these GeV gamma rays have remained elusive, presenting a perplexing conundrum for astrophysicists.

The inability to detect these gamma rays has led to various theories, one of which posits that weak intergalactic magnetic fields may redirect the lower-energy gamma rays away from our observational line. Alternatively, another hypothesis rooted in the principles of plasma physics suggests that as the electron–positron pairs travel through the sparse matter between galaxies, they could undergo instability. This instability could amplify small fluctuations, generating magnetic fields that further disturb the beam and dissipate energy.

To evaluate these competing theories, the research group, which comprises experts from the University of Oxford and the Science and Technology Facilities Council’s Central Laser Facility (CLF), undertook a series of experiments. They utilized CERN’s High-Radiation to Materials (HiRadMat) facility to produce electron–positron pairs with high precision and introduced them into a controlled plasma environment. This setup served as a laboratory analogue for the cascading pair processes seen in blazar jets. Through meticulous measurements of the beam profile and the associated magnetic field signatures, the team sought to directly gauge whether beam-plasma instabilities would significantly disrupt the properties of the jet.

The results surprised the research team, as they found that the electron-positron pair beam maintained a remarkably stable and narrow profile, deviating very little or not at all from its intended trajectory. This observation significantly curtails the possibility that beam-plasma instabilities contribute to the apparent absence of GeV gamma rays. In extrapolating their laboratory findings to astronomical contexts, the team suggested that the intergalactic medium likely harbors a magnetic field that has its origins in the early universe.

Professor Gianluca Gregori, the lead researcher from the Department of Physics at the University of Oxford, articulated the significance of these findings. He emphasized how laboratory experiments can bridge theoretical predictions with observational data, enhancing our comprehension of celestial phenomena observed from both ground-based and satellite telescopes. His statement underlined the collaborative nature of this work, which underscores the vital role of international partnerships in traversing unexplored territories in high-energy physics.

However, the implications of this study extend beyond mere clarification of certain astrophysical mysteries. The early universe, understood to have been homogeneous and isotropic, presents additional questions about the genesis of antiquated magnetic fields. The research team hints at the possibility of new physics beyond the traditional Standard Model, indicating that future exploration could unveil further insight into the universe’s formative conditions.

Co-investigator Professor Bob Bingham from the STFC’s Central Laser Facility echoed the importance of their work, explaining how laboratory astrophysics can provide a unique testing ground for theories concerning the dynamics of high-energy cosmic phenomena. By simulating conditions similar to those found in cosmic jets, the experiments afford scientists the opportunity to quantify processes that potentially shape these jets’ evolution and elucidate the nature of magnetic fields in intergalactic locales.

Further contributions to this endeavor were made by Professor Subir Sarkar, also from the University of Oxford. He expressed enthusiasm for participating in such a cutting-edge experiment, underscoring that their striking findings invite broader interest in plasma astrophysics. By marrying high-energy laboratory physics with cosmic inquiries, the team hopes to unlock fundamental questions that have long eluded researchers.

This collaborative project brought together an impressive assembly of institutions and expertise, involving researchers from the University of Oxford, STFC’s Central Laser Facility, CERN, the University of Rochester’s Laboratory for Laser Energetics, AWE Aldermaston, Lawrence Livermore National Laboratory, the Max Planck Institute for Nuclear Physics, the University of Iceland, and Instituto Superior Técnico in Lisbon. This multifaceted approach highlights the global effort in addressing profound astrophysical questions with an array of perspectives.

In conclusion, the team’s groundbreaking findings not only chisel away at the obscurities surrounding the missing gamma rays associated with blazar jets but also challenge existing paradigms regarding cosmic magnetic fields. As the research unfolds, and with upcoming facilities like the Cherenkov Telescope Array Observatory poised to provide higher-resolution data, future experiments will likely drive deeper investigations into these critical astrophysical queries.

Subject of Research: Plasma fireballs and blazar jets
Article Title: Suppression of pair beam instabilities in a laboratory analogue of blazar pair cascades
News Publication Date: 3 November 2025
Web References: DOI: 10.1073/pnas.2513365122
References: Proceedings of the National Academy of Sciences (PNAS)
Image Credits: Gianluca Gregori

Keywords

Plasma physics, blazars, gamma rays, electron-positron pairs, high-energy astrophysics, cosmic magnetic fields, CERN, Super Proton Synchrotron, intergalactic medium.

Neutron stars, remnants of massive stars that have undergone supernova explosions, are characterized by their small size and massive density. They often exhibit the behavior of strong gravitational fields that impact the surrounding space-time. The current revelation about the winds emanating from these neutron stars has brought forth a compelling insight into their energetic ballet. On February 25, 2024, XRISM’s Resolve instrument turned its eyes to GX13+1, a notoriously bright X-ray source in our galaxy, drawn from a surrounding accretion disk of agitated hot matter spiraling toward the star’s surface.

The research team anticipated their observations would reveal crucial details about the dense winds birthed from neutron stars, hoping to enhance understanding of cosmic mechanics. They theorized that similar processes generate outflows from both neutron stars and the supermassive black holes dispersed across the cosmos. Although the luminous winds might seemingly behave comparably, initial observations hinted at fundamental differences that challenge existing models of cosmic outflows and their influence on galactic evolution.

What unfolded was a scientific marvel; the RXISM data revealed that the winds emitted from GX13+1 were denser than anticipated, igniting discussions regarding their formation processes. Matteo Guainazzi, ESA’s XRISM project scientist, expressed his excitement upon evaluating the data, noting that the findings could potentially shift paradigms in astrophysical research. Such winds play critical roles in regulating star formation and influencing the broader cosmic structure, acting as agents of feedback in galactic evolution.

One particularly astonishing finding during the observations was the appearance of a brightening in GX13+1 just days prior to the scheduled XRISM observation. This surge reached levels surpassing a known threshold, termed the Eddington limit, which defines a maximum luminosity where the outward radiation pressure equals the gravitational force holding matter in place. This phenomenon signifies a remarkable state where the infalling matter is vigorously converted into winds, transforming our understanding of matter dynamics around neutron stars.

As the observations commenced, scientists witnessed the neutron star generating intense energy output, propelling a thick, massive wind at around 1 million kilometers per hour, a fast pace relative to terrestrial speeds, yet disappointingly slow compared to the anticipated velocities. Chris Done from Durham University, a key figure in the research, reflected on the unexpected nature of the wind’s velocity and thickness, equating the phenomenon to gazing at the sun through a thick fog where clarity was compromised despite an apparent surge in brightness.

Interestingly, past data from supermassive black holes subjected to the Eddington limit reported winds reaching speeds of 20 to 30 percent of the speed of light. This highlighted the stark contrast between the wind mechanisms at play in neutron star systems and their supermassive counterparts, raising critical questions about how these systems, governed by similar forces, could result in such differing behaviors.

Delving deeper into the findings, the research team has posited that the core factor influencing the wind characteristics could be the thermal dynamics of the surrounding accretion disk. An important contrast to consider is that while supermassive black holes generally have larger accretion disks, they also operate at lower temperatures compared to their stellar counterparts. These larger disks, though luminous, spread their power across broader spans, releasing energy primarily in the form of lower-energy ultraviolet light, unlike the more potent X-rays from smaller mass systems.

The implications of these findings are profound, offering fertile grounds for advancing theoretical frameworks regarding cosmic winds and their interactions. The XRISM mission’s high-resolution technology heralds an era of enhanced observational capabilities, fostering explorations that delve into previously elusive details of astrophysical phenomena. As these insights collectively foster an evolving understanding of cosmic mechanics, they hold the potential to shed light on the overarching forces governing the evolution of galaxies.

As researchers continue to sift through the impressive datasets returned by XRISM, the mission has set the stage for the future development of high-resolution X-ray telescopes such as the NewAthena project. These next-generation instruments promise to deepen investigations of cosmic bodies and phenomena on an intimate scale, further unraveling the complexities that lie within the cosmic tapestry.

In conclusion, the observations made by XRISM have sparked a pivotal moment in astrophysics, not only confirming existing theories about cosmic winds but also challenging and reshaping them. The mission’s ability to capture the intimate details of phenomena like GN13+1’s winds represents a leap forward in understanding how the interplay of matter, energy, and gravity drives the formation and evolution of structures in the universe.

Subject of Research: Cosmic Winds from Neutron Stars
Article Title: Stratified wind from a super-Eddington X-ray binary is slower than expected
News Publication Date: 17-Sep-2025
Web References: Nature
References: Nature
Image Credits: Credit: ESA

Keywords

Cosmic Winds, Neutron Stars, XRISM, Eddington Limit, Accretion Disks, Astrophysics, Galactic Evolution, High-Resolution X-ray Astronomy.