Washington: Astronomers claim to have identified the moment when a black hole in our galaxy launched super-fast knots of gas into space.

Racing outward at about one-quarter the speed of light, these "bullets" of ionised gas are thought to arise from a region located just outside the black hole's event horizon, the point beyond which nothing can escape.

"Like a referee at a sports game, we essentially rewound the footage on the bullets' progress, pinpointing when they were launched," said Gregory Sivakoff of University of Alberta in Canada, who led a team which used observations from NASA's Rossi X-ray Timing Explorer satellite.

The research centred on the mid-2009 outburst of a binary system known as H1743-322, located about 28,000 light-years away toward the constellation Scorpius.

Discovered in 1977, the system is composed of a normal star and a black hole of modest but unknown masses. Their orbit around each other is measured in days, which puts them so close together that the black hole pulls a continuous stream of matter from its stellar companion.

The flowing gas forms a flattened accretion disk millions of miles across, several times wider than our sun, centred on the black hole. As matter swirls inward, it is compressed and heated to tens of millions of degrees, so hot it emits X-rays.

Some of the infalling matter becomes re-directed out of the accretion disk as dual, oppositely directed jets. Most of the time, the jets consist of a steady flow of particles.

"This research provides new clues about the conditions needed to initiate a jet and can guide our thinking about how it happens," said Chris Done at University of Durham.