LHAASO unveils galactic treasure map: breakthroughs in ultra-high-energy gamma-ray astronomy

China’s Large High Altitude Air Shower Observatory (LHAASO), a major scientific infrastructure, has released groundbreaking results from its "Mini Survey of the Milky Way" program. With unprecedented sensitivity, LHAASO has revealed a spectacular panorama of ultrahigh-energy gamma rays within our galaxy, providing new insights into the origins of cosmic rays, their propagation, and extreme astrophysical processes. This marks humanity’s entry into a new era of ultrahigh-energy gamma-ray astronomy.

Cosmic rays are relativistic charged particles from space, carrying information about extreme astrophysical environments such as supernova remnants(SNR), pulsar wind nebulae(PWN), and young massive star clusters(YMC). With energies up to a billion times higher than those produced by human-made accelerators, they hint at the existence of natural "super accelerators" in the universe. Where are these accelerators? What are they? How do they accelerate particles? And how do these particles reach Earth? These questions have remained unsolved for a century since the discovery of cosmic rays. The origin of cosmic rays is listed by the U.S. National Science and Technology Council as one of the 11 most pressing scientific questions of the 21st century.

Studying cosmic-ray origins is challenging because their charged nature means their paths are scrambled by interstellar magnetic fields. The key lies in detecting neutral gamma photons—cosmic "pointers" unaffected by magnetic fields—produced when cosmic rays collide with interstellar matter.

LHAASO, the world’s most sensitive ultrahigh-energy gamma-ray detector, is a Chinese-designed and -built facility. It consists of a square-kilometer array (KM2A) of 5,216 electromagnetic particle detectors and 1,188 muon detectors, complemented by a water Cherenkov detector array (WCDA) and a wide-field Cherenkov telescope array (WFCTA). Together, these instruments capture gamma rays across an energy range from teraelectronvolts (TeV) to petaelectronvolts (PeV). When gamma rays strike Earth's atmosphere, they trigger a cascade of particles—like a cosmic 'rain shower.' LHAASO acts as a massive 'raindrop collector,' spanning a square kilometer in area. By capturing these particle 'raindrops,' scientists can reconstruct detailed images of the gamma-ray sky.

The galactic plane, teeming with cosmic-ray accelerators and dense interstellar matter, serves as both a gamma-ray hotspot and a natural laboratory for probing extreme astrophysical phenomena. Leveraging its unmatched sensitivity and broad energy coverage, LHAASO has conducted the first systematic observations of ultrahigh-energy gamma-ray sources along the Milky Way’s disk, taking a major step toward solving the "century-old mystery" of cosmic-ray origins.

“Mini Survey of the Milky Way” has yielded four new discoveries:

​​Star-Forming Region W43​​: LHAASO detected gamma rays exceeding hundreds of TeV in W43, a stellar nursery accounting for 10% of the Milky Way’s total star formation rate. The 50-light-year-wide emission zone aligns with a central young massive star cluster and surrounding dense gas, suggesting stellar winds and supernova shocks accelerate particles to near-light speeds. The region stores cosmic-ray energy exceeding 2.5×10^48 erg (equivalent to 20 million years of the Sun’s total radiation), confirming massive stellar activity as a key cosmic-ray accelerator.

​​PWN in Supernova Remnant CTA-1​​: Observations of CTA-1 (4,600 light-years away) reveal 300 TeV gamma rays primarily from its central PWN. Theoretical models suggest the accelerated electrons approach the energy limits predicted for PWN shock acceleration. Multiwavelength data show particles are convectively transported by the pulsar wind, with an average magnetic field of ~4.5 microgauss—surprisingly weak compared to traditional "strong magnetic confinement" models.

​​Young Pulsar Halo Candidate​​: Around the 62,400-year-old pulsar J0248+6021, LHAASO detected diffuse gamma-ray emission spanning 29–49 light-years. Its morphology suggests either a PWN or a pulsar halo—a structure formed by high-energy electrons diffusing into interstellar space. As the youngest pulsar halo candidate yet found, this discovery helps scientists understand how pulsars transition from PWNe to halos and inject energy into the interstellar medium, challenging current models of cosmic-ray propagation.

Mystery Source 1LHAASO J0056+6346u​​: This unidentified ultrahigh-energy source is surrounded by gas bubbles potentially linked to young massive star clusters or supernova remnants. Hidden pulsar activity may drive the radiation, awaiting confirmation via future X-ray and multiwavelength studies.

"LHAASO is revolutionizing our understanding of the Milky Way and challenging traditional cosmic-ray theories," notes Prof. Elena Amato of Italy's Arcetri Astrophysical Observatory. The research team likens these discoveries to a "Rosetta Stone" for decoding the physics of the extreme universe. The research findings have been published as a special collection in Science China Physics, Mechanics & Astronomy. The team acknowledges all contributors and looks forward to collaborating with scientists worldwide to explore the unsolved mysteries of the high-energy universe.

 

See the articles：

LHAASO view of the Milky Way

https://doi.org/10.1007/s11433-025-2638-5

 

Study of ultra-high-energy gamma-ray source 1LHAASO J0056+6346u and its possible origins

https://doi.org/10.1007/s11433-024-2661-8

 

LHAASO detection of very-high-energy γ-ray emission surrounding PSR J0248+6021

https://doi.org/10.1007/s11433-024-2508-5

 

Deep view of composite SNR CTA1 with LHAASO in γ-rays up to 300 TeV

https://doi.org/10.1007/s11433-024-2479-4

 

Observation of the γ-ray emission from W43 with LHAASO

https://doi.org/10.1007/s11433-024-2477-9

 

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