June 12, 2013
New Class Of Stars Identified Through Minute Variations In Brightness
Lee Rannals for redOrbit.com - Your Universe OnlineAstronomers writing in the journal Astronomy & Astrophysics say they have discovered a new type of variable star.
The Swiss astronomers discovered the new class of variable stars by measuring minute variations in stellar brightness. The new results are based on regular measurements of the brightness of more than three thousand stars in the open star cluster NGC 3766 over a period of seven years. They were able to reveal how 36 of the cluster's stars followed an unexpected pattern in tiny variations in their brightness at the level of 0.1 percent of the stars' normal brightness.
According to the researchers, the observed variations had a period between about two and 20 hours. The stars are somewhat hotter and brighter than the Sun.
“We have reached this level of sensitivity thanks to the high quality of the observations, combined with a very careful analysis of the data,” says Nami Mowlavi, leader of the research team, “but also because we have carried out an extensive observation program that lasted for seven years. It probably wouldn´t have been possible to get so much observing time on a bigger telescope.”
Many stars are known as variable because their apparent brightness changes over time. How the brightness of these stars change depend on properties of their interiors.
“The very existence of this new class of variable stars is a challenge to astrophysicists,” says Sophie Saesen, another team member. “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 behavior of this strange new type of star.”
The team is still unsure what causes the variability within the stars, but they spin at speeds that are more than half of their critical velocity.
“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,” explains Mowlavi. “We hope our discovery will encourage specialists to address the issue in the hope of understanding the origin of these mysterious variations.”
This isn't the first time astronomers have identified a new type of star in the last decade. In 2006 astronomers of the University of Manchester´s Jodrell Bank Observatory led an international team to find a new kind of cosmic object which sends out radio flashes. These flashes are very short and rare, lasting for just one-hundredth of a second.