Over 70 years after Indian astrophysicist and Nobel laureate Subrahmanyan Chandrasekhar predicted that rapidly rotating stars would emit polarised light, scientists in Australia have observed the phenomenon for the first time.
Researchers from the University of New South Wales (UNSW) in Australia and University College London in the UK used a highly sensitive piece of equipment to detect the polarised light from Regulus, one of the brightest stars in the night sky.
The equipment provided unprecedented insights into the star, which is in the constellation Leo, allowing the scientists to determine its rate of spinning and the orientation in space of the star’s spin axis.
“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 Daniel Cotton, from the UNSW.
“It is spinning at approximately 320 kilometres per second - equivalent to travelling from Sydney to Canberra in less than a second,” said Cotton.
In 1946, Chandrasekhar had predicted the emission of polarised light from the edges of stars, prompting the development of sensitive instruments called stellar polarimeters to try to 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.
“The instrument we have built, the High Precision Polarimetric Instrument (HIPPI) is the world’s most sensitive astronomical polarimeter,” Cotton said.
“Its high precision has allowed us to detect polarised light from a rapidly spinning star for the first time,” he 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,” he added.
It has previously been extremely difficult to measure these properties of rapidly rotating stars, researchers said.
Yet the information is crucial for understanding the life cycles of most of the hottest and largest stars in the galaxies, which are the ones that produce the heaviest elements, such as iron and nickel, in interstellar space, they said.
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.
The study was published in the journal Nature Astronomy.
