'Heartbeat Stars' Unlocked in New Study
http://www.nasa.gov/feature/jpl/heartbeat-stars-unlocked-in-new-study
Heartbeat stars, discovered in large numbers by NASA's Kepler space telescope, are binary stars (systems of two stars orbiting each other)
that got their name because if you were to map out their brightness over time, the result would look like an electrocardiogram, a graph of
the electrical activity of the heart. Scientists are interested in them because they are binary systems in elongated elliptical orbits.
This makes them natural laboratories for studying the gravitational effects of stars on each other.
In a heartbeat star system, the distance between the two stars varies drastically as they orbit each other. Heartbeat stars can get as close
as a few stellar radii to each other, and as far as 10 times that distance during the course of one orbit.
At the point of their closest encounter, the stars’ mutual gravitational pull causes them to become slightly ellipsoidal in shape, which is
one of the reasons their light is so variable. This is the same type of "tidal force" that causes ocean tides on Earth. By studying heartbeat
stars, astronomers can gain a better understanding of how this phenomenon works for different kinds of stars.
Tidal forces also cause heartbeat stars to vibrate or "ring" -- in other words, the diameters of the stars rapidly fluctuate as they orbit
each other. This effect is most noticeable at the point of closest approach.
