Astronomers have said what at first looked like an upside-down planet has revealed a new method for studying binary star systems.
Working with UW astronomer Eric Agol, doctoral student Ethan Kruse has confirmed the first "self-lensing" binary star system-one in which the mass of the closer star can be measured by how powerfully it magnifies light from its more distant companion star. Though our Sun stands alone, about 40 percent of similar stars are in binary (two-star) or multi-star systems, orbiting their companions in a gravitational dance.
Kruse was looking for transits others might have missed in data from the planet-hunting Kepler Space Telescope when he saw something in the binary star system KOI-3278 that didn't make sense.
The two stars of KOI-3278, about 2,600 light-years (a light-year is 5.88 trillion miles) away in the Lyra constellation, take turns being nearer to Earth as they orbit each other every 88.18 days. They are about 43 million miles apart, roughly the distance the planet Mercury is from the Sun. The white dwarf, a cooling star thought to be in the final stage of life, is about Earth's size but 200,000 times more massive.
That increase in light, rather than the dip Kruse thought he'd see, was the white dwarf bending and magnifying light from its more distant neighbor through gravitational lensing, like a magnifying glass.
"The basic idea is fairly simple," Agol said. "Gravity warps space and time and as light travels toward us it actually gets bent, changes direction. So, any gravitational object-anything with mass-acts as a magnifying glass," though a weak one. "You really need large distances for it to be effective."
This finding improves on research in 2013 by the California Institute of Technology, which detected a similar self-lensing effect minus the brightening of the light because the two stars being studied were much closer together.
The paper has been published in journal Science.
