Energetic gamma rays spotted from 'microquasar'

After decades of searching, astronomers have confirmed that a gluttonous stellar remnant that glows brightly in X-rays can create high-energy gamma rays as well. The tiny powerhouse could serve as a nearby laboratory to study how particles are accelerated in the universe's biggest black holes.

Cygnus X-3, a pair of objects that sit some 30,000 light years from Earth, has long been a puzzle. The system is thought to contain the dense remnant of a star – either a black hole or a neutron star – that is feeding on a disc of material stolen from a companion star.

The pair orbit each other once every 4.8 hours, shining in X-rays and occasionally sending jets of material, or flares, outwards at close to the speed of light. Because of these flares, Cygnus X-3 has been dubbed a "microquasar", since it resembles quasars, the flaring supermassive black holes at the centres of some galaxies.

Interest in Cygnus X-3 has grown since the flares were first discovered by radio telescopes in 1972. In the following decades, astronomers have found hints that gamma rays – the universe's highest-energy photons – could be coming from Cygnus X-3 with energies as high as trillions or even quadrillions of electronvolts (eV).

But these detections remained tentative, in part because the flares, which occur every year or so, are unpredictable. Until now, no one has found gamma rays stemming from Cygnus X-3 that had energies higher than 300,000 eV, gamma rays that are only slightly more energetic than the highest-energy X-rays, says Marco Tavani of the Space Astrophysics and Cosmic Physics Institute in Rome, Italy.

"People claimed to have detected high-energy emission from Cygnus X-3 on many occasions, but these reports were never confirmed," Tavani told New Scientist. "For many years, people thought it was a sort of damned object."