Bright lights

Chilean telescope reveals whole new class of stars

New discoveries from the La Silla Observatory in the Atacama pose challenges to current astrophysics theory.

Thursday, July 11, 2013  
The star cluster NGC 3766. Photo by ESO. The star cluster NGC 3766. Photo by ESO.


Representing the forefront of ground-based observation technology, Chile’s ALMA and VLT telescopes have been hogging the astronomy headlines in recently. Yet a little telescope in Coquimbo caused a big a stir in the astrophysics community last month.

Operating out of the European Southern Observatory’s (ESO) La Silla Observatory in northern Chile, Swiss researchers using the 1.2 m Euler telescope recorded mysterious irregularities when measuring minute variations in stellar brightness in 36 variable stars in the star cluster NGC 3766.

A variable star is a star whose brightness (as seen from Earth) fluctuates, either due to its luminosity actually changing, or due to objects passing in front of it. According to ESO, the 36 stars, which all burn brighter than our Sun, fluctuate from their normal brightness levels to 0.1 percent below that level for a stretch of time that would last between two and 20 hours. According to existing models, stars brightness should not fluctuate in this way at all.

“The very existence of this new class of variable stars is a challenge to astrophysicists,” Sophie Saesen, a team member on the study, said. “Current theoretical models predict that their light is not supposed to vary periodically at all, so our current efforts are focused on finding out more about the behaviour of this strange new type of star.”

According to ESO, although the cause of the variability remains unknown, there is one clue: some of the stars seem to be fast rotators. They spin at speeds that are more than half of their critical velocity, which is the threshold where stars become unstable and throw off material into space.

“In those conditions, the fast spin will have an important impact on their internal properties, but we are not able yet to adequately model their light variations,” lead researcher Nami Mowlavi of Geneva Observatory Mowlavi explained. “We hope our discovery will encourage specialists to address the issue in the hope of understanding the origin of these mysterious variations.”

The study took regular measurements of the brightness of over three thousand stars in the cluster over a period of seven years. The level of precision achieved during the study was twice that of comparative studies using other telescopes, and Mowlavi put this partly down to the observation time afforded to the team at Chile’s La Silla Observatory.

“We have reached this level of sensitivity thanks to the high quality of the observations, combined with a very careful analysis of the data, and also because we have carried out an extensive observation program that lasted for seven years,” Mowlavi said. “It probably wouldn’t have been possible to get so much observing time on a bigger telescope.”

Chile is fast becoming the world’s top destination for this groundbreaking research. Due to its almost non-existent humidity and clear skies, the Atacama Desert is the world’s premier location for astronomy. The country overall is home to almost half the world’s telescope infrastructure, and this is set to increase to over two thirds in the next decade.