An international team of scientists has found the first gamma-ray binary in a nearby galaxy and the most luminous one ever seen, using data from NASA's Fermi Gamma-ray Space Telescope.
The dual-star system, dubbed LMC P3, contains a massive star and a crushed stellar core that interact to produce a cyclic flood of gamma rays, the highest-energy form of light.
"Fermi has detected only five of these systems in our own galaxy, so finding one so luminous and distant is quite exciting," said lead researcher Robin Corbet at NASA's Goddard Space Flight Centre in the US.
"Gamma-ray binaries are prized because the gamma-ray output changes significantly during each orbit and sometimes over longer time scales," said Corbet.
These rare systems contain either a neutron star or a black hole and radiate most of their energy in the form of gamma rays.
LMC P3 is the most luminous such system known in gamma rays, X-rays, radio waves and visible light, and it is only the second one discovered with Fermi, researchers said.
The system lies within the expanding debris of a supernova explosion located in the Large Magellanic Cloud (LMC), a small nearby galaxy about 163,000 light-years away.
The surface of the star at the heart of LMC P3 has a temperature exceeding 33,000 degrees Celsius, or more than six times hotter than the Sun's.
The star is so luminous that pressure from the light it emits actually drives material from the surface, creating particle outflows with speeds of several million miles an hour.
In gamma-ray binaries, the compact companion is thought to produce a "wind" of its own, one consisting of electrons accelerated to near the speed of light.
The interacting outflows produce X-rays and radio waves throughout the orbit, but these emissions are detected most strongly when the compact companion travels along the part of its orbit closest to Earth.
Through a different mechanism, the electron wind also emits gamma rays. When light from the star collides with high-energy electrons, it receives a boost to gamma-ray levels.
Called inverse Compton scattering, this process produces more gamma rays when the compact companion passes near the star on the far side of its orbit as seen from our perspective.