MIT Prof. Joshua Winn on multiple stars, coplanar systems, and radius of instability
Can observations of circumbinary planets provide more information about the stars? What are the properties of planetary orbits in binary star systems? Associate Professor of Physics at Massachusetts Institute of Technology Joshua Winn speaks on eclipses in system of several bodies.
Certainly there are lots of double star systems where we see two stars orbiting each other very tightly but we didn’t know whether those double star systems had planets. You can make arguments either way. There’s no reason why you would be forbidden from forming planets around such stars. On the other hand we didn’t know of any specific examples and so we just were curious. Do such planets exist? Do “circumbinary” planets exist? It wasn’t until 2010 that we had very clear inconclusive evidence that such planets do exist.The first really direct piece of evidence came from the Kepler space telescope.
What’s interesting about the circumbinary planets is that as soon as you get outside that radius of instability, you find planets quite regularly, they’re not especially rare, you don’t have to look very far out in the system, you just have to look barely a little bit further than where they can’t exist and then you start finding these planets. And that tells me that these planets must be very common. The processes that make these planets must be such that it’s not so unusual because we see them just as soon as we could possibly see them as we move out further from the centers of the systems.
We only know of about 10 binary star systems that have planets going around both stars. And of those in all but one case I believe there’s only one planet that’s known and that planet exists in the very innermost orbit that it could possibly exist in and still be stable. However there is one system that’s become known as Kepler-47 where there is more than one planet going around a pair of stars. And that’s interesting, it suggests that may be planetary systems of 9 or 10 planets exist around pairs of stars or even triples of stars. It’s just that we have to be patient, it’s much more difficult to discover the distant planets than it is the closer planets.