Researchers made regular measurements of the brightness of stars in the open star cluster NGC 3766 over a period of seven years. Their study, published in the journal Astronomy & Astrophysics, shows that 36 of these stars followed an unexpected pattern.
These stars' brightness varied by 0.1 percent at regular intervals, for periods lasting between about two and 20 hours.
The extraordinary precision in the measurements from their comparatively small 1.2 meter telescope is twice as good as that achieved by comparable studies from other telescopes -- sufficient to reveal these variations for the first time.
Nami Mowlavi, leader of the research team, credits the discovery to "the high quality of the observations, combined with a very careful analysis of the data," but also notes that it helped having seven years of continuous observation.
"It probably wouldn't have been possible to get so much observing time on a bigger telescope," Mowlavi said.
Many stars are known as variable or pulsating stars, because their apparent brightness changes depending on the properties of their interiors. This phenomenon has led to a branch of astrophysics called asteroseismology.
The cause of the variability of the as yet unnamed class of stars remains unknown, but the data show that some of the stars seem to be fast rotators, spinning at more than half their critical velocity -- the threshold where stars become unstable and throw off material into space.
"The very existence of this new class of variable stars is a challenge to astrophysicists," said Sophie Saesen, another team member. "Current theoretical models predict that their light is not supposed to vary periodically at all."