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Astronomers probe source of mysterious powerful radio signal from beyond galaxy

India January 12(IM): Fast radio bursts beaming from beyond our galaxy, are astonishingly powerful, and nobody knows what – or who – is making them.Now an international team of astronomers, including Australian scientists, have made a discovery that could start to unravel the mystery.

In a cover story published in Nature on Thursday, they report the bursts are coming from one of the most extreme and unusual objects ever seen – possibly a tiny but powerful star trapped in a field of ionised gas that has been spun off by a nebula, or been ejected from a supernova."We don't really know what's producing these bursts," says Dr Charlotte Sobey​, an astronomer at the International Centre for Radio Astronomy Research and CSIRO who worked on the discovery. "But they have enormous power. As much energy is released in a single millisecond as the sun releases in a single day."FRBs, as they are known, have fascinated astronomers since they were discovered in the archive data of NSW's Parkes radio telescope in 2007.Enormously powerful bursts of radio waves that last for milliseconds, they have defied explanation for years – leading some to suggest they are the communications of some distant alien civilisation.The team that made the discovery have been studying FRB 121102, an FRB source unique because its signal keeps repeating over and over.They called in Dr Sobey, an expert in the rotation of light, when they noticed the signal had a unique attribute: extreme polarisation.Polarised light is light that vibrates in only one direction. Light from the sun is unpolarised – its electric charges vibrate in multiple directions. Polarised glasses let in light that vibrates in only one direction, which is why they make things darker.Dr Sobey immediately saw the light she had been asked to look at was very unusual. It was extremely polarised, about as polarised as any radio source can be.More unusually, the light had been "twisted", she says, hitting the Earth like a corkscrew. This is usually caused by light moving through an extremely strong magnetic field generated by a field of dense ionised gas, known as plasma.Dr Sobey realised she was looking at an "extreme object".The FRB's polarisation points to one of two sources.Most likely, the bursts are being generated by a tiny but energetic star that has become trapped within the dense plasma cloud of a powerful nebula. The star's polarised light is being twisted by the surrounding plasma before it reaches us.That, or the star is trapped near a super-massive black hole, which could produce similar effects.While the mystery is far from solved, Dr Sobey believes the evidence is now firmly stacked against FRBs being generated by alien life."I personally don't think it could be aliens. We have seen these FRBs come from lots of different directions in the sky, and we think it's very unlikely there are many different civilisations spread throughout this range in the universe that would all communicate using the same kind of technique."It also needs a lot of power to generate these type of signals, so we think it must be of astrophysical origin."

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