Observatory lifts veil on nebula secret

Scientists discover powerful particle accelerator at heart of exploded star

An international team led by Chinese scientists has found proof that the Crab Nebula is an ultra-powerful particle accelerator that can accelerate an electron to 2.3 peta-electron volts－more than 230 times higher than the most powerful accelerator on Earth－according to a study published in the journal Science on Thursday.

Expert said the new data is approaching the theoretical limit of classical electrodynamics in astrophysics and provides key insights on the origin of ultra-high-energy particles, something that has puzzled scientists for decades. The study was led by the Chinese Academy of Sciences' Institute of High Energy Physics.

The discovery was made using the Large High Altitude Air Shower Observatory, or LHAASO. An extensive assembly of detectors and telescopes covering more than 1.36 square kilometers, it is located at an altitude of 4,410 meters in Daocheng county, Sichuan province.

The Crab Nebula is located about 6,500 light-years from Earth. It is the remnant of a massive star whose explosion was recorded by astronomers on Earth in 1054, making it the first supernova remnant identified by modern astronomy with a clear historical record.

Scientists believe the nebula harbors an energetic, fast-rotating pulsar, which is a type of superdense celestial object known as a neutron star.

The fast-spinning magnetic field of the pulsar creates a powerful wind that can accelerate surrounding particles to staggering energy levels.

The latest discovery was made possible when LHAASO detected a photon with 1.1 PeV, or 1.1 million billion electron volts, in January.

Such photons are created when high-energy electrons lose their energy in the magnetic field, and scientists later calculated the energy of the parent electron for the detected photon was 2.3 PeV, said Cao Zhen, LHAASO's chief scientist.

"This proves that within the core region of the nebula lies an extremely powerful electron accelerator," he said, adding the size of the accelerator is estimated to be about 5,000 astronomical units, or 748 billion kilometers.

The Crab Nebula has fascinated astronomers for decades because it is one of the extremely rare celestial sources that can produce radiation in all energy bands, from radio waves to infrared, ultraviolet and gamma rays, he said.

Now, with LHAASO's discovery, scientists can start probing the ultra-high-energy band of the nebula with more reliable and accurate results, which may yield new knowledge in high-energy astrophysics, Cao said.

"We are expected to detect one to two photons with energies around 1 PeV from the Crab Nebula every year, and the puzzle of the cosmic PeV electron accelerator should be unraveled in the coming years," he said.