Dangerous pinwheel

Earth could be in for a neighborhood dispute with a death star, according to an Australian astronomer. A spectacular rotating pinwheel system just down the astronomical road from Earth — 8,000 light years away — includes an unstable Wolf-Rayet star that could explode. Eight years ago, WR104 was discovered in the constellation Sagittarius by Sydney University astronomer Peter Tuthill.
A Wolf-Rayet star is the last step on the way to a supernova — the explosion of a star at the end of its life. Images from the Mauna Kea in Hawaii telescope show that every eight months the two stars at the centre of the pinwheel orbit each other, leaving a trail of hot gas, carbon and dust. "Viewed from Earth, the rotating tail appears to be laid out on the sky in an almost perfect spiral," Tuthill said. "It could only appear like that if we are looking nearly exactly down on the axis of the binary system." Tuthill and his team worry this box-seat view might put us in the firing line when the system finally explodes."Sometimes, supernovae like the one that will one day destroy WR104 focus their energy into a narrow beam of very destructive gamma-ray radiation along the axis of the system," he warns. "If such a 'gamma-ray burst' happens, we really do not want Earth to be in the way." Even a short gamma-ray burst at supernova strength could zap away half the Earth's ozone layer, drastically increasing the amount of deadly space radiation that penetrates our atmosphere. One leading theory blames the Ordovician mass extinction of 443 million years ago on such an interstellar gamma-ray burst. There's no need to move planets just yet, however, because Tuthill is uncertain whether Earth is precisely on WR104's axis. We probably have hundreds of thousands of years before it blows, so we have plenty of time to come up with some answers," he said.
Tuthill's research is published in the latest edition of the Astrophysical Journal.



University of Sydney
A composite of 11 images of Wolf-Rayet 104, an unstable binary star system that could direct a deadly burst of gamma rays at Earth.