'Upside-Down' Planet Shows Astronomers New Technique to Study Binary Star Systems

What first appeared to be a type of upside-down planet may have just given scientists the clues they need to develop a new method for studying binary star systems. The planet has allowed researchers to confirm 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.

While our sun stands along, about 40 percent of similar stars are in binary (two-star) or multi-star systems. The stars orbit one another in a type of gravitational dance. Yet many of these systems are located so far away that their planets are difficult to detect and examine directly. That's why scientists use other techniques in order to learn more about these planets.

In this case, an astronomer was looking for transits, which is when a planet passes in front of its host star, causing a slight dimming of light. This allows researchers to detect the planets in star systems. Yet in this case, the astronomer spotted something unusual.

"I found what essentially looked like an upside-down planet," said Ethan Kruse, the astronomer looking for planets, in a news release. "What you normally expect is the dip in brightness, but what you see in this system is basically the exact opposite-it looks like an anti-transit."

What Kruse saw was actually a white dwarf, a star, bending and magnifying light from its more distant neighbor through gravitational lensing like a magnifying glass. This allowed researchers to actually measure the mass of the closer, white dwarf star.

Gravitational lensing has been used before to detect planets around distant stars before. Yet until now, the process has only been used in the fleeting instances of a nearby and distant star, not otherwise associated in any way. This latest instance, though, shows that the technique can be used with two orbiting stars. This is especially interesting since while normal gravitational lensing is a chance encounter, self-lensing occurs on a regular basis and gives astronomers more than one opportunity to make observations.

The findings reveal a new way to potentially study star systems in the future. By using binary and multi-star systems, researchers can learn more about our universe.

The findings are published in the journal Science.