More than 70 years after Indian astrophysicist and Nobel laureate Subrahmanyan Chandrasekhar first predicted the emission of polarised light from the edges of stars, a team of scientists have for the first time observed rapidly rotating stars emitting polarised light.The researchers detected polarised light from Regulus, one of the brightest stars in the night sky, which is in the constellation Leo.
The research has provided unprecedented insights into the star,allowing the scientists to determine its rate of spinning and the orientation in space of the star’s spin axis, according to the study published in the journal Nature Astronomy.
“We found Regulus is rotating so quickly it is close to flying apart, with a spin rate of 96.5 per cent of the angular velocity for break-up,” said study first author Daniel Cotton from University of New South Wales (UNSW), Sydney, Australia.
“It is spinning at approximately 320 kilometres per second – equivalent to travelling from Sydney to Canberra in less than a second,” Cotton added.
Chandrasekhar’s prediction in 1946 prompted the development of sensitive instruments called stellar polarimeters to try and detect this effect.
Optical polarisation is a measure of the orientation of the oscillations of a light beam to its direction of travel.
In 1968, other researchers built on Chandrasekhar’s work to predict that the distorted, or squashed shape, of a rapidly rotating star would lead to the emission of polarised light, but its detection has eluded astronomers until now.
For this study, the researchers used a highly sensitive piece of equipment designed and built at UNSW Sydney and attached to the Anglo-Australian Telescope at Siding Spring Observatory in westernNew South Wales to detect the polarised light from Regulus.
“The instrument we have built, the High Precision Polarimetric Instrument, HIPPI, is the world’s most sensitive astronomical polarimeter. Its high precision has allowed us to detect polarised light from a rapidly spinning star for the first time,” Cotton said.
“We have also been able to combine this new information about Regulus with sophisticated computer models we have developed at UNSW to determine the star’s inclination and rotation rate,” Cotton added.
Regulus is about 79 light years away. During the total solar eclipse in the US in August, Regulus was just one degree away from the Sun and was, to many people, the only star visible during the eclipse.
Picture courtesy: Alamy