Astronomers have detected the highest-energy light ever seen, streaming in from near the center of the Milky Way. Hundreds of gamma ray signals were detected with ultra-high energies, with the most powerful signals crossing the Peta-electronvolt (PeV) threshold – much higher than thought possible in our galaxy.
Gamma rays are the most energetic type of electromagnetic radiation, released during extreme events like supernovae, matter-antimatter annihilation, and the activity of objects like pulsars. They’re often detected with energies in the Giga-electrovolt (GeV) range, but they’ve been known to occasionally top the Tera-electronvolt (TeV) mark, which is 1,000 GeV.
In 2019, the Crab Nebula stole the crown for most energetic gamma rays ever detected, at 100 TeV. That was considered pretty close to the upper limit for how energetic sources could ever get in our Milky Way – but now that ceiling has been utterly shattered.
Astronomers using the Large High Altitude Air Shower Observatory (LHAASO) in China have now detected gamma rays with energies higher than 1 PeV – that’s 1,000 TeV, or 10 times higher than the previously presumed maximum for our galaxy.
The team identified 530 ultra-high energy photons from 12 sources, with energies up to around 1 PeV. The highest reaches an astonishing 1.4 PeV, making it the highest energy photon ever observed. The team was able to trace this record-breaking radiation to an active star-forming region in the constellation Cygnus.
The team calls these powerful cosmic particle accelerators “PeVatrons,” although it remains unknown exactly how photons can be accelerated to such intense energies. Their exact sources haven’t yet been identified either, but the astronomers say they seem to be linked to star formation, nebulae, and/or supernova remnants. Further observations of these kinds of objects could allow scientists to better understand the origins of cosmic rays.
And this is just the beginning, too – the LHAASO is still under construction, and these discoveries were made using the first observation run using only half of the detection array. Once the rest of the facility comes online, these questions can be probed even more deeply.
The research was published in the journal Nature.
Source: Chinese Academy of Sciences