Heartbeat star

Artist's conception of two heartbeat stars and a companion star (NASA/JPL-Caltech)

Heartbeat stars are pulsating variable binary star systems with vibrations caused by tidal forces. The name "heartbeat" comes from the similarity of the light curve of the star with what a heartbeat looks like through an electrocardiogram if their brightness was mapped over time. Many heartbeat stars have been discovered with the Kepler Space Telescope.

Orbital information

Heartbeat stars are binary star systems in which each star rotates in a highly elliptical orbit around the common mass center, and 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 one orbit. As the star with the more elliptical orbit swings closer to its companion, gravity will pull the star into a non-spherical shape, changing its light output. When the stars reach the point of their closest encounter, the mutual gravitational pull between the two stars will cause them to become slightly ellipsoidal in shape, which is the reason for their light being so variable.

Discoveries

The Kepler Space Telescope has discovered large numbers of heartbeat stars. One of the stars discovered, KOI-54, has been shown to increase in brightness every 41.8 days. A subsequent study in 2012 characterized 17 additional objects from the Kepler data which were classified as heartbeat stars. A study published in the Astrophysical Journal, which measured the orbits of 19 heartbeat star systems, found that surveyed heartbeat stars tend to be both bigger and hotter than the Sun.