Eclipses shine light on 3-star 'solar' system

An unusual, distant triple-star system has been observed in intimate detail with help from Canadian researchers and a B.C. telescope.

The system, nicknamed Trinity, is about 800 light years away and contains two red dwarfs, each smaller than our sun, that circle each other every 0.9 days. Together, the pair orbits a red giant, which is 12.4 times the size of our sun, every 45 days, said a paper published in Science Friday.

What is particularly unusual is that astronomers have observed light pulsations of the red giant that appear to be because of gravitational effects similar to ocean tides on the Earth caused by the pull of the moon.

"Pulsations are actually driven by these little stars going around the big star," said Gordon Sarty, a University of Saskatchewan astronomer who co-authored the paper.

That is a phenomenon that has never been seen before. Previously, the only thing known to cause light pulsations is a combination of ionization — the loss or gain of electrons from atoms — and convection in very large, old stars. The convection of gases within a star is similar to the movement of hot water and bubbles inside a pot on the stove.

Planet-hunting telescope

The research was led by Aliz Derekas, an astronomer at Eotvos University and Konkoly Observatory in Budapest, Hungary. Her team used data from the planet-hunting Kepler telescope to get information about pulsating stars.

The pulsations provide information about stars similar to information about the Earth provided by observations of earthquakes.

"You can get an idea of what's inside the star," Sarty said.

Derekas and her colleagues stumbled upon unusual signals from the three-star system. They contacted Sarty and University of Victoria astronomer David Balam and asked for some help in figuring out what was happening.

Sarty and Balam took measurements from the National Research Council's Dominion Astrophysical Observatory in Victoria, B.C. Based on the specific colours of light they observed with a technique called spectroscopy, they figured out that the red dwarfs circled the bigger star every 45 days.

While single-star systems like our own solar system and binary systems with two stars are common, less than 800 triple-star systems are known and only one features stars as close together as these three.

Lucky eclipses

The details of such far-away systems are very hard to observe, but in this case researchers were lucky, Sarty said — the stars orbit in a plane that lines up with our line of sight, eclipsing each other every orbit.

The eclipses cause variations in brightness that allowed researchers to get information about their orbits that would otherwise be impossible to obtain.

"This kind of discovery is serendipitous," Sarty said.

He added that it's increasingly difficult to get government grants for the kind of basic research in Canada that leads to this type of surprise discovery, which is why the Canadian component of the research was funded by the American Astronomical Society.