A groundbreaking new survey from China’s LHAASO observatory has unveiled powerful ultrahigh-energy gamma-ray emissions across the Milky Way.
China’s Large High Altitude Air Shower Observatory (LHAASO), a leading scientific facility, has unveiled remarkable findings from its “Mini Survey of the Milky Way” project. Utilizing its extraordinary sensitivity, LHAASO has captured a stunning and detailed view of ultrahigh-energy gamma rays within our galaxy.
These observations offer valuable clues about the origins and movement of cosmic rays, as well as the extreme phenomena that generate them. Scientists view this breakthrough as a milestone that ushers in a new chapter in the exploration of ultrahigh-energy gamma-ray astronomy.
Cosmic rays are highly energetic charged particles that travel through space at nearly the speed of light. They originate in extreme environments such as supernova remnants (SNR), pulsar wind nebulae (PWN), and young massive star clusters (YMC). The energy levels of these particles can exceed those produced by even the most powerful human-made accelerators by up to a billion times, suggesting the presence of natural “super accelerators” somewhere in the universe.
Despite a century of study since their discovery, fundamental questions about cosmic rays remain unanswered. Where exactly are these powerful accelerators located? What are their physical properties? How do they propel particles to such extreme energies, and how do those particles eventually reach Earth? These mysteries continue to challenge scientists. In fact, the U.S. National Science and Technology Council has ranked the origin of cosmic rays among the top 11 most critical scientific questions of the 21st century.
Gamma Rays: The Cosmic Clues
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.
Key Discoveries from the Milky Way Survey
“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.
References: “LHAASO view of the Milky Way” by Elena Amato, 11 April 2025, Science China Physics, Mechanics & Astronomy.
DOI: 10.1007/s11433-025-2638-5
Reference: “Study of ultra-high-energy gamma-ray source 1LHAASO J0056+6346u and its possible origins” by LHAASO Collaboration, 20 May 2025, Science China Physics, Mechanics & Astronomy.
DOI: 10.1007/s11433-024-2661-8
“LHAASO detection of very-high-energy γ-ray emission surrounding PSR J0248+6021” by LHAASO Collaboration, 21 January 2025, Science China Physics, Mechanics & Astronomy.
DOI: 10.1007/s11433-024-2508-5
“Deep view of composite SNR CTA1 with LHAASO in γ-rays up to 300 TeV” by LHAASO Collaboration, 17 January 2025, Science China Physics, Mechanics & Astronomy.
DOI: 10.1007/s11433-024-2479-4
“Observation of the γ-ray emission from W43 with LHAASO” by LHAASO Collaboration, 21 January 2025, Science China Physics, Mechanics & Astronomy.
DOI: 10.1007/s11433-024-2477-9
Reference: “Editorial” by Ruizhi Yang, and Zhen Cao, 24 April 2025, Science China Physics, Mechanics & Astronomy.
DOI: 10.1007/s11433-025-2655-y
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