George Lucas’s fictional planet Tatooine may not be so unusual, after all. In the late 1970s, Lucas dreamt up a desert world made hot and dry by the two suns it orbited. Little did he know that, nearly 40 years later, astronomical observations and computer models would reveal potentially thousands of exoplanets in binary systems.
Between Hubble, Kepler, and other efforts, astronomers have discovered nearly 2,000 exoplanets. We’ve also discovered many, many binary systems right here in our own galaxy—estimates range from a few percent to 85%, depending on whom you ask. Given those numbers, Elliott Horch, an astronomer at Southern Connecticut State University, and his team were curious how many of those exoplanets might orbit binary stars.
Here’s Phil Plait, writing at Bad Astronomer:
To see what they could see, the astronomers relied on an old method called speckle interferometry. Basically, the Earth atmosphere roils over our heads, with little packets of air flying this way and that. When light from a star passes through them, it gets bent this way and that as well due to refraction. This happens many times per second, so when you take a long exposure the light blurs into a disk. Astronomers call this (confusingly) “seeing.” It’s also why stars appear to twinkle.
But there’s a way around this. Over time the light rays get smeared out, but if you take lots of extremely fast exposures, you freeze that motion out. It’s like taking super slo-mo video. Instead of a big disk, you get a bunch of near-perfect images of the star that jump around in location from image to image, but each frame is a nice, extremely high res shot of the star.
From those high-res images, Horch and his colleagues were able to directly detect a large number of exoplanet systems with two stars. Unfortunately, not all of the images were clear enough to make a definitive conclusion in every case, so the team ran some simulations to estimate what they were missing. In total, they think up to 40-50% of stars with exoplanets are binary systems.
While some exoplanets orbit close binaries, a la Tatooine, not all of these exoplanets orbit both stars simultaneously. Many are orbiting a single star which also happens to have a second star in orbit, often very far out. In that case, the sky of the exoplanet wouldn’t be bathed in the light of two relatively equal suns, but instead would have one dominant and another dimmer sun, almost like a very close star.
The paper has been accepted for publication in the Astrophysical Journal, though given the wide range of estimates for the number of binary star systems in the Milky Way, I’ll be curious to see how this latest finding holds up.