The enigmatic flash appears red and yellow in this view from Swift’s X-ray and ultraviolet/optical telescopes (Image: NASA/Swift/Stefan Immler)

It was bright, fierce and thankfully short. A mysterious event in a distant galaxy has blasted our solar system with the most powerful burst of X-rays ever recorded, temporarily blinding an astronomical satellite.

At 0303 GMT on 21 June, a sudden burst of X-rays struck the Swift spacecraft, the mission team reported on Wednesday.

X-rays from space are absorbed by Earth’s atmosphere, so pose no danger on the ground. However, Swift orbits Earth at an altitude of 600 kilometres, where the blast was so intense that it overwhelmed the spacecraft’s X-ray detector. It also confused the software that analyses the mission’s data on the ground, says David Burrows of Pennsylvania State University in University Park, the mission’s chief scientist.


“[The software] basically threw up its hands and said, ‘Something must be wrong, because the data doesn’t make sense,'” he says.

Puzzling pummelling

Swift’s records show that at its peak, the burst pummelled the spacecraft with 143,000 X-ray photons per second. That made it nearly 15 times as bright as Scorpius X-1, a neutron star 9000 light years from Earth that is normally the brightest X-ray object in the sky. The burst dimmed rapidly during its first few seconds but continued glowing for about 10 minutes.

This powerful beginning was probably the most powerful X-ray flash ever recorded, Burrows says. An X-ray flash observed in 1979 may have appeared brighter – the comparison is hard to make because the 1979 flash was observed by a different spacecraft – but only because it occurred in a nearby galaxy, just 160,000 light years from Earth. By contrast, the June flash was traced to a vastly more distant galaxy 5 billion light-years away.

No one knows what caused the burst, but a clue lies in the fact that it accompanied a lengthy burst of gamma rays from deep space. Swift’s purpose is to determine the origin of such bursts using three telescopes that detect gamma rays, X-rays, and ultraviolet and visible light. Long gamma-ray bursts are thought to be due to jets of matter shooting out almost at the speed of light from a star that is collapsing to form a black hole: the same type of event may have caused the recent X-ray burst.

However, shock waves from these violent events normally produce around 10 to 100 X-ray photons per second, so the Swift team is at a loss to explain why this X-ray burst was more than 1000 times brighter than this.

“We’re very puzzled – we don’t understand it yet,” Burrows says. “Every once in a while something comes along that’s completely unexpected and this is one of them.”