The stellar system Cygnus X-3 could accelerate protons to colossal energies of several tens of peta-electronvolts. This conclusion is based on gamma rays detected up to 3.7 PeV in Earth’s atmosphere.
Cygnus X-3 lies about 24,000 light-years away, in the constellation Cygnus. It pairs a massive star with a compact object, probably a black hole or a neutron star. Matter flows between the two stars and feeds powerful jets.
Overview of Cygnus X-3: the WN 4-6 type star (in blue) and the compact object surrounded by an accretion disk (in red).
Image Wikimedia
The researchers used LHAASO, a vast observatory installed in China. It does not directly detect accelerated protons: it observes the particle showers produced in Earth’s atmosphere by extremely energetic gamma rays coming from space.
The data reveal gamma rays received from this part of the sky ranging from 0.06 to 3.7 PeV. This variability matches that of Cygnus X-3’s emissions. A possible modulation linked to the system’s orbit also appears.
The gamma rays could be produced when accelerated protons encounter surrounding matter. In this so-called hadronic interpretation, the protons must reach several tens of PeV to arrive with such energy on Earth. The system would then become a “super-PeVatron”, capable of reaching extreme energies.
Future simultaneous observations in gamma rays, X-rays and radio waves will need to clarify the mechanism at play. They will also be able to verify the orbital modulation and determine whether Cygnus X-3 truly contributes to the most energetic cosmic rays in our galaxy.