In space, no one can hear you scream — which is no bad thing, because scientists have discovered that it is a lot filthier than they thought.

Researchers revealed yesterday that limitless stretches of space are strewn with interstellar soot, making it harder to see very distant objects such as exploding stars or supernovae.

The finding, reported in the US journal Science, is more than a matter of cosmic cleanliness. Proof of the existence of space soot raises serious questions about the mysterious "dark energy" that is thought to drive the expansion of the universe.

In the late 1990s, astronomers noticed that light from very distant supernovae was dimmer than it should be, suggesting that some of these dying stars were far further away than theories predicted. The puzzle led to the hypothesis that the expansion of the universe was accelerating, and was being pushed along by an unknown form of energy, which they called dark energy.

The latest study suggests that space soot might be to blame, at least in part, for making distant stars appear more faint than expected.

'Like dust in front of a lens'

"We're not saying this explains dark energy, but we're saying this stuff is out there and like dust in front of a lens, it might make these objects appear dimmer than they are," said Andrew Steele at the Carnegie Institution for Science in Washington DC.

Steele and his colleague Marc Fries made their discovery while examining three meteorites that formed shortly after the birth of the solar system 4.5bn years ago.

Using a powerful microscope, they identified graphite "whiskers" only a few thousandths of a millimetre long embedded in minerals that form in the ancient heat of newborn suns and exploding stars. "These whiskers are like rolled-up tubes of graphite and they could be generated in supernovae and blown out into space, or they could be thrown out of newborn stars," said Steele.

When the sun was very young, the solar wind — which is a stream of energetic particles — was exceptionally strong and could have blown vast clouds of graphite whiskers far out into space. The same may have happened around other stars, leaving a haze of soot throughout space.

Speculation in Sixties

In the early 1960s, Chandra Wickramasinghe, a space scientist now at Cardiff University's Centre for Astrobiology, and the late Sir Fred Hoyle first speculated that carbon whiskers might pervade space. "There's no question that carbon whiskers like these now discovered would dim starlight and light from distant supernovae, and [the dimming] has been one of the kingpins of the dark energy argument," said Wickramasinghe.

Andy Fabian at Cambridge University's Institute of Astronomy said there was substantial evidence for dark energy that cannot be explained by cosmic soot, but said it should still be investigated.

"Dust plays a huge role in what we can see in the universe. We can't see very far through the disc of our own galaxy because of dust and if there's another type of dust out there that is widespread and important, then we need to know about it," he said.