Secrets of bright, rapidly spinning star revealed

Secrets of bright, rapidly spinning star revealed
August's total eclipse of the sun with the star Regulus visible as a blue dot in the lower left corner. The photograph was taken in Casper, Wyo. Credit: jmsands57.

Almost 50 years after it was first predicted that rapidly rotating stars would emit polarised light, a UNSW Sydney-led team of scientists has succeeded in observing the phenomenon for the first time.

They used a highly sensitive piece of equipment designed and built at UNSW and attached to the Anglo-Australian Telescope at Siding Spring Observatory in western NSW to detect the polarised light from Regulus, one of the brightest stars in the .

The research has 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.

The study, by a team at UNSW, University College London, University of Washington and University of Hertfordshire, is 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," says study first author and UNSW scientist Dr Daniel Cotton, of the School of Physics.

"It is spinning at approximately 320 kilometres per second - equivalent to travelling from Sydney to Canberra in less than a second."

Indian astrophysicist and Nobel laureate Subrahmanyan Chandrasekhar first predicted the emission of polarised light from the edges of stars in 1946, prompting 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.

"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," says Dr Cotton.

"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.

"It has previously been extremely difficult to measure these properties of rapidly rotating stars. Yet the information is crucial for understanding the life cycles of most of the hottest and largest in the galaxies, which are the ones that produce the heaviest elements, such as iron and nickel, in interstellar space."

Regulus is about 79 years away. During the in the US in August, Regulus was just 1 degree away from the Sun and was, to many people, the only star visible during the eclipse.


Explore further

X-rays reveal temperament of possible planet-hosting stars

More information: Daniel V. Cotton et al, Polarization due to rotational distortion in the bright star Regulus, Nature Astronomy (2017). DOI: 10.1038/s41550-017-0238-6
Journal information: Nature Astronomy

Citation: Secrets of bright, rapidly spinning star revealed (2017, September 18) retrieved 17 July 2019 from https://phys.org/news/2017-09-secrets-bright-rapidly-star-revealed.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
211 shares

Feedback to editors

User comments

Sep 18, 2017
Hmm, would the size of the gas cloud a star formed from determine the star's spin rate?

Sep 18, 2017
"The stars with a faster rotation have more objects.. ("The objects without an independent rotation (such as Venus, Mercury, etc.) can't direct the other objects into their gravitational field." orbiting around themselves.
If the speed of rotation increases, the conditions for an asteroid belt to exist are created.
The stars with (a very) fast rotation have a disk of gas ..

The stars with a very fast rotation around their axes have an increased emission of radiation at their poles, which sometimes can vary, due to the increased influx of matter into cyclone or a faster whirl " http://www.global...ture.pdf

Sep 18, 2017
Here is a suggestion for those who write the headings of these phys.org articles. Please don't dumb the topic down!

"Secrets of bright, rapidly spinning star revealed" is generic click-bait There no secret anyway. There is an observation which confirms a hypothesis proposed many years ago. Something like "Rapidly spinning star's polarized light observed for the first time" would be much better.

Please don't assume that your audience has no scientific knowledge or curiosity or that contrived phrases devoid of scientific information are more enticing or useful than a succinct statement of the discovery.

Thanks for all the articles on physics, astronomy, biology and medicine!

Sep 19, 2017
The research has 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.

Actually, Robin, there were secrets that were revealed. Please read articles more carefully.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more