The discovery emerged from a coordinated campaign between two of China’s flagship observatories: the Einstein Probe, a space-borne X-ray telescope, and the Large High Altitude Air Shower Observatory, known as LHAASO, which sits at high altitude in Sichuan province and detects the showers of secondary particles produced when ultrahigh-energy gamma rays strike Earth’s atmosphere. Together, the two instruments observed PSR J1740+1000, a middle-aged pulsar located roughly 4,600 light-years from Earth. What they found was an X-ray tail of unprecedented length, stretching southwest from the pulsar for about 32 arcminutes on the sky, which translates to approximately 42 light-years at the pulsar’s distance. This is the longest X-ray tail ever associated with a pulsar wind nebula.

The significance of the measurement lies in how it transforms our picture of particle transport. The prevailing assumption has long been that once high-energy particles escape their acceleration sites, magnetic turbulence in interstellar space scatters them rapidly, causing them to diffuse isotropically, meaning equally in all directions. Under that model, any directional structure should be erased within a relatively short distance of the source. The new observations defy that expectation. Over a scale of tens of light-years, the particles streaming away from PSR J1740+1000 maintain a coherent propagation direction, leaving behind an elongated trail of synchrotron X-ray emission that astronomers can read like a breadcrumb path.

The story began with earlier observations by the XMM-Newton satellite, which had detected an X-ray tail several light-years long in the vicinity of the pulsar. But XMM-Newton’s field of view and observing strategy limited how much of the structure it could capture. The Follow-up X-ray Telescope aboard the Einstein Probe, by contrast, was designed with a wide field of view and a low instrumental background, making it exceptionally well suited to searching large swaths of sky for faint, diffuse X-ray structures. In roughly 70,000 seconds of observations, the Einstein Probe revealed that the tail extends far beyond what XMM-Newton had seen. Remarkably, although XMM-Newton accumulated more than six times the observing time, it detected only a small fraction of the full structure, underscoring how much of the high-energy sky may still be hiding beyond the edges of conventional surveys.

The crucial connection came from LHAASO. In recent years, the observatory has catalogued a series of ultrahigh-energy gamma-ray sources, some of which reach energies exceeding one petaelectronvolt, a million billion electronvolts, produced by particles accelerated in the vicinity of supernova remnants, pulsars, and black holes. A persistent puzzle has been that several of these gamma-ray sources have no obvious astronomical counterpart nearby, no pulsar, remnant, or stellar cluster that could plausibly serve as their engine. These so-called orphan sources have been difficult to interpret. One possibility is that the parent particles simply traveled far from their acceleration site before producing detectable gamma rays, meaning the visible emission marks a waypoint on a long journey rather than the point of origin.

PSR J1740+1000 provides a striking confirmation of that idea. The ultrahigh-energy gamma-ray emission detected by LHAASO extends in the same direction as the newly mapped X-ray tail, and the two structures match closely in position on the sky. More importantly, the physical interpretation ties them together at the level of the particles themselves. The electrons responsible gain enormous energies within the pulsar wind nebula, the bubble of magnetized plasma that a rapidly spinning neutron star blows into its surroundings. As these electrons propagate along the tail, they spiral through magnetic fields and emit synchrotron radiation, a portion of which falls into the X-ray band and is recorded by the Einstein Probe. Simultaneously, the same electrons collide with low-energy photons that pervade interstellar space and boost them to extreme energies through inverse Compton scattering, producing the ultrahigh-energy gamma rays that LHAASO detects from the ground.

In effect, the X-rays and gamma rays are two footprints left by a single population of high-energy electrons, imprinted in different wavelength bands along the same path. The spatial alignment and the consistency of the energy spectra of the two emissions provide strong evidence that the extraordinarily long tail is genuinely the record of extended particle propagation, not a chance superposition of unrelated structures. For the first time, astronomers can follow a coherent trail of PeV-scale particles across a distance comparable to the spacing between neighboring stars in the galactic neighborhood, connecting the accelerator directly to the far-flung region where its particles finally reveal themselves.

Why the particles hold their direction over such vast distances remains an open question, and the researchers propose two candidate mechanisms. The first is that the interstellar magnetic field in this region is highly ordered, allowing the electrons to stream efficiently along the field lines while suppressing motion perpendicular to them, effectively creating a narrow magnetic track through the galaxy. The second is that a fast, collimated outflow, perhaps a jet-like wind, is continuously ejected from the pulsar wind nebula in that direction, carrying the particles outward the way water from a fire hose carries a jet far from its nozzle. The current data cannot yet distinguish between these scenarios, but both lead to the same consequential conclusion: high-energy particles do not always scatter into randomness within a short distance of their source, and anisotropic transport can persist across scales of tens of light-years.

The implications reach well beyond a single pulsar. As Gabriele Ponti and colleagues at the Italian National Institute for Astrophysics note in a commentary published in the same issue of the journal, the significance of the discovery extends past PSR J1740+1000 itself, because it demonstrates that a spatial offset between an ultrahigh-energy gamma-ray source and its candidate astronomical counterpart does not necessarily mean the association is false. Instead, such an offset may trace the propagation path of particles after they leave their acceleration site. In other words, the location where astronomers detect gamma rays may be merely the footprints of a long journey, not the birthplace of the particles. This reframing could resolve the identities of several of LHAASO’s orphan sources and reshape how scientists match gamma-ray detections to their astrophysical engines.

The study also stands as a demonstration of the power of coordinated, multiwavelength astronomy. By pairing a wide-field X-ray telescope in orbit with a ground-based gamma-ray observatory covering an entirely different energy regime, the research team stitched together a continuous physical narrative, following particles from the turbulent environment near a neutron star across 42 light-years of interstellar space. Each band captures a different stage of the electrons’ lives: synchrotron light marks their passage through magnetic fields close to the source, while inverse Compton gamma rays record their later interactions with ambient starlight far from it. As surveys by the Einstein Probe and LHAASO continue, astronomers expect this approach to uncover more such trails, opening a new window onto how the galaxy’s most extreme accelerators seed interstellar space with particles whose energies dwarf anything achievable in human laboratories, and gradually dismantling a century-old mystery one footprint at a time.

Subject of Research: Anisotropic propagation of high-energy cosmic-ray electrons from the pulsar wind nebula PSR J1740+1000, traced by joint X-ray and gamma-ray observations

Article Title: Einstein probe and LHAASO reveal a 42-light-year directed journey of cosmic rays

Article References: Einstein probe and LHAASO reveal a 42-light-year directed journey of cosmic rays. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: cosmic rays, pulsar wind nebula, PSR J1740+1000, Einstein Probe, LHAASO, X-ray astronomy, ultrahigh-energy gamma rays, synchrotron radiation, inverse Compton scattering, interstellar magnetic fields, particle transport, high-energy astrophysics

Pulsar wind nebulae have long been understood as cosmic bubbles filled with a sea of relativistic particles, energized by the rotational slow-down—or spindown—of rapidly spinning neutron stars known as pulsars. The Crab Nebula, situated in our Milky Way galaxy, has historically held the distinction of being the most powerful PWN, demonstrated by its role as a persistent emitter of multiwavelength radiation, including gamma rays reaching PeV energies. These high-energy emissions are thought to result from charged particles accelerated to near light speed through complex interactions within the nebula’s magnetic and electric fields. The recent detection of a similar, yet more extreme, phenomenon in the PWN powered by PSR J1849−0001 now forces astrophysicists to rethink the mechanisms enabling such efficient particle acceleration.

Located within a relatively lesser-known pulsar, PSR J1849−0001’s spindown power is approximately 50 times weaker than that of the Crab pulsar. Yet, contrary to expectations, the associated PWN—dubbed the ‘Aquila Booster’—exhibits a UHE gamma-ray spectrum extending beyond 100 TeV, reaching PeV energies. This discovery was made possible thanks to LHAASO’s unparalleled capability in detecting extensive air showers produced by these extremely energetic photons interacting with Earth’s atmosphere. The identification of this point-like gamma-ray source with such a hard spectral tail definitively establishes APSR J1849−0001’s PWN as a natural PeV particle accelerator on par and even surpassing the Crab Nebula’s output in total gamma luminosity.

This remarkable finding has profound implications for the physics of particle acceleration in PWNe. Traditional scenarios typically model the pulsar and its wind nebula under ideal magnetohydrodynamics (MHD), where magnetic and electric fields govern particle dynamics in a predictable, steady-state fashion. In these models, the efficiency of converting the rotational energy of the pulsar to ultra-relativistic particles is expected to be well below unity, limited by radiative losses and shock-induced acceleration mechanisms. However, the extremely high acceleration efficiency inferred in the Aquila Booster suggests that this simplistic approach fails to capture crucial physical processes occurring in the nebula, particularly upstream of the termination shock—the boundary where the pulsar wind abruptly slows down due to interaction with the surrounding medium.

The ultra-relativistic electrons and positrons accelerated within the PWN upscatter ambient low-energy photons to gamma-ray energies via inverse Compton scattering, producing the observed UHE gamma rays. The spectrum’s power-law behavior, extending smoothly to and beyond the PeV regime, indicates an efficient and continuous acceleration process rather than episodic or stochastic injections. By analyzing multiwavelength data, especially X-rays obtained through sensitive space telescopes, researchers can constrain the average magnetic field within the nebula to about 3 microgauss (μG). This low magnetic field intensity is strikingly different from that within the Crab Nebula, where the magnetic field is stronger, suggesting fundamentally different environmental and dynamical conditions inside the Aquila Booster.

Further insight comes from detailed X-ray observations, which trace the synchrotron emission from the highest-energy electrons spiraling in magnetic fields. The synchrotron spectrum’s shape and intensity provide vital clues about the electron energy distribution and magnetic field strengths, enabling precise modeling of the acceleration and cooling timescales. The Aquila Booster’s X-ray emission confirms the presence of multi-TeV electrons undergoing rapid acceleration, consistent with the demanding conditions needed to generate PeV gamma rays seen in the very-high-energy domain. This enables auroral-like conditions, where electrons efficiently gain energy at rates competing with radiation and escape mechanisms, an unusual circumstance in typical PWN environments.

The challenge now lies in understanding the physical processes responsible for such extraordinary acceleration efficiencies close to or even exceeding unity—an efficiency metric that approaches the theoretical maximum. The observations imply non-ideal MHD effects must be playing an influential role in the acceleration region, with magnetic reconnection emerging as a prime candidate. Magnetic reconnection occurs when the magnetic field topology rearranges explosively, releasing vast amounts of stored magnetic energy and enabling localized regions where charged particles undergo rapid acceleration. If reconnection events are occurring upstream of the termination shock in the Aquila Booster, they would provide the energy and dynamics necessary for the production of ultrahigh-energy particles.

This new paradigm suggests that the acceleration region within the PWN might be far more dynamic and turbulent than previously envisioned, potentially marked by complex geometries and transient structures facilitating particle energization beyond standard shock acceleration. The involvement of magnetic reconnection would provide a direct pathway to explain both the efficient conversion of rotational energy into relativistic particles and the generation of gamma rays reaching PeV energies. Such mechanisms could reshape our broader understanding of cosmic accelerators and high-energy astrophysical phenomena in environments dominated by magnetized plasma.

The detection itself, made possible by LHAASO’s innovative hybrid array, highlights the observatory’s sensitivity at the highest photon energies and cements its role as a leader in very-high-energy astrophysics. The facility’s robust capabilities to monitor the northern sky for air showers generated by gamma rays above 10 TeV enable the systematic discovery of sources operating at energies approaching 1 PeV. This in turn opens new windows into exploring the extreme universe, pushing the boundaries of particle physics and astrophysics. The identification of the Aquila Booster underscores the importance of all-sky, wide-field gamma-ray observatories in uncovering rare and energetic cosmic phenomena.

Looking forward, the discovery of the Aquila Booster motivates further multiwavelength campaigns to dissect this source in unprecedented detail. Complementary observations by X-ray, radio, and gamma-ray telescopes can help refine the spatial and temporal characteristics of the acceleration sites within the nebula. Moreover, theoretical and computational efforts focusing on non-ideal MHD effects, particle-in-cell simulations of magnetic reconnection, and plasma turbulence in PWNe will be critical to unraveling the complex processes at play. This renewed focus may reveal similar yet previously undetected extreme accelerators elsewhere in our galaxy and beyond.

The implications for astroparticle physics are equally profound. Observations of UHE gamma rays serve as indirect signatures of ultrarelativistic cosmic rays whose origins remain enigmatic. Understanding how PWNe like the Aquila Booster produce such energetic particles could illuminate the sources contributing to the high-energy cosmic ray spectrum observed at Earth, which spans energies up to and beyond the PeV scale. Hence, the Aquila Booster may represent a prototype of a class of natural accelerators fundamental to cosmic ray astrophysics, bridging gaps between particle acceleration theories, gamma-ray astronomy, and cosmic ray physics.

Furthermore, the discovery challenges the notion that spindown power alone dictates a PWN’s extreme particle acceleration potential. The Aquila Booster demonstrates that relatively modest pulsars may still generate extraordinarily luminous UHE gamma-ray sources if the local physical conditions favor efficient magnetic reconnection and acceleration. This realization compels astronomers to revisit population synthesis models of PWNe and to search systematically for additional “hidden” accelerators powered by less energetic pulsars, broadening the census of astrophysical particle accelerators.

The present findings draw a new roadmap for future observational and theoretical endeavors. LHAASO’s detection capabilities, coupled with next-generation high-energy observatories like the Cherenkov Telescope Array (CTA) and space-based X-ray telescopes, will enable deeper exploration of PWNe and their acceleration mechanisms. By comparing PWNe of varied pulsar powers, ages, and environments, researchers will strive to decode the conditions essential for shaping the highest-energy accelerators in our cosmic neighborhood. The Aquila Booster stands as a touchstone in this quest and a testament to the unyielding quest to understand the universe’s most extreme natural laboratories.

In conclusion, the identification of the Aquila Booster as an extreme particle accelerator powered by PSR J1849−0001 not only extends the frontiers of known astrophysical accelerators but also compels a reevaluation of theoretical frameworks governing pulsar wind nebulae physics. The extraordinary acceleration efficiency approaching unity challenges conventional wisdom and signals a critical role for non-ideal magnetohydrodynamic processes, notably magnetic reconnection, in accommodating and sustaining ultrahigh-energy particle populations. As research advances, this discovery promises to unravel the enigmatic workings of nature’s most energetic engines and illuminate the processes shaping the high-energy universe.

Subject of Research: Extreme particle acceleration in pulsar wind nebulae (PWNe), demonstrated through ultrahigh-energy (UHE) gamma-ray emission from PSR J1849−0001’s PWN.

Article Title: An extreme particle accelerator powered by pulsar PSR J1849−0001.

Article References:
The LHAASO Collaboration. An extreme particle accelerator powered by pulsar PSR J1849−0001. Nat Astron (2026). https://doi.org/10.1038/s41550-026-02839-0

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41550-026-02839-0