Australasian Science: Australia's authority on science since 1938

Black Hole Reveals the Corkscrew Nature of Light

An international team of astronomers has measured circular polarisation in the bright flash of light as a dying star collapsed to a black hole almost 11 billion years ago.

Gamma-ray bursts are the brightest objects in the entire Universe, only lasting a fraction of a second but sending out as much energy in that time as the Sun will in its entire life. These bursts are emitted by dying stars collapsing to black holes that form jets of material travelling at over 99.995% of the speed of light.

Dr Peter Curran from the Curtin University node of the Inter­national Centre for Radio Astronomy Research described gamma-ray burst 121024A as “an unusual case. Its light had a strange feature – it was circularly polarised.”

Light waves that are polarised move in a uniform way as they travel, either bouncing up and down or left and right for linear polarisation, or in a spiral motion in the case of circular polarisation.

“Most light in the natural world is unpolarised – the waves are bouncing around at random,” Curran said. “But the light from this gamma-ray burst … was about 1000 times more polarised than we expected.

“This is the first time we’ve found circular polarisation in the light from a gamma-ray burst, but we think we’ll find it in more bursts in the future, so we can start to pin down what’s actually happening when these bright flashes of energy are released.”

The research was published in Nature.