A fast-rotating star named Regulus, which is one of the brightest stars in the sky, is spinning so quickly that it may end up destroying itself. This polarised light-emitting star has been observed by the astronomers for the first time.
The phenomenon was first predicted more than 50-years-ago, however, has dodged our instruments until now. Finally, they have now confirmed the crazy spinning speed of the star in light of these findings.
So, what is polarised light and why this finding is a big deal? For this, we need to backtrack a little. Light waves normally travel in the direction of their choice as they hit and bounce off objects. However, light waves can also be polarised, a process in which they all get rotated in a particular direction.
Astronomers J Patrick Harrington and George W Collins II predicted in 1968 that polarised light would be emitted by a rapidly rotating star because its shape gets distorted into a squished oblate shape as it spins too fast.
Their idea was based on calculations done by Nobel-winning physicist Subrahmanyan Chandrasekhar in 1946. He first predicted that some stars could be emitting polarised light.
A range of instruments aimed at detecting polarisation in the interstellar space were developed following these predictions. But polarisation from a fast-spinning star was not caught until now.
And now, an international team from Australia, the US, and the UK has discovered it using a highly sensitive polarimeter developed at the University of New South Wales (UNSW) in Sydney.
"The High Precision Polarimetric Instrument, HIPPI, is the world's most sensitive astronomical polarimeter," says one of the team, astronomer Daniel Cotton from UNSW.
HIPPI’s eye caught Regulus, a blueish first-magnitude star 79 light-years away, located in the constellation Leo. Regulus has been ranked as the 22nd brightest star in the night sky.
Astronomers had previously extrapolated the rotation rate of the star on the basis of models calculated for other stars of its types. However, this interpretation couldn’t be confirmed in the absence of more observations directly from Regulus.
The first-ever detection of polarised light from a rapidly rotating star has revealed that Regulus is spinning at 320 kilometres per second (199 miles per second). It is spinning so fast that it is close to breaking itself up.
"We found Regulus is rotating so quickly it is close to flying apart, with a spin rate of 96.5 percent of the angular velocity for break-up," says Cotton.
"Previously, the field has been largely restricted to studying material external to stars or those with extreme magnetic fields," the team writes in the study.
"Now we are able to probe fundamental parameters of the stellar atmosphere itself."
The findings have been published in Nature Astronomy.