Heartbeat stars are

pulsating variable A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

binary star systems in eccentric orbits with vibrations caused by

tidal force The tidal force is a gravitational effect that stretches a body along the line towards the center of mass of another body due to a gradient (difference in strength) in gravitational field from the other body; it is responsible for diverse phenomen ...

s. The name "heartbeat" comes from the similarity of the

light curve In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...

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 The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized Exoplanet, planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocen ...

Orbital information

Heartbeat stars are binary star systems where each star travels in a highly elliptical

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...

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 100 times that distance during one orbit. As the star with the more elliptical orbit swings closer to its companion, gravity will stretch the star into a non-spherical shape, changing its apparent light output. At their closest point in orbit, the tidal forces cause the shape of the heartbeat stars to fluctuate rapidly. 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 one of the reasons for their observed brightness being so variable.

Discoveries

Heartbeat stars were studied for the first time on the basis of OGLE project observations. The

with its long monitoring of the brightness off hundreds of thousands of stars enabled the discovery of many heartbeat stars. One of the first binary systems discovered to show the elliptical orbits, 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 and united them as a class of binary stars. A study which measured the rotation rate of star spots on the surface of heartbeat stars showed that most heartbeat stars rotate slower than expected. A study which measured the orbits of 19 heartbeat star systems, found that surveyed heartbeat stars tend to be both bigger and hotter than the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. The star HD 74423, discovered using NASA's

Transiting Exoplanet Survey Satellite Transiting Exoplanet Survey Satellite (TESS, Explorer 95 or MIDEX-7) is a space telescope for NASA's Explorer program, designed to search for exoplanets using the transit method in an area 400 times larger than that covered by the ''Kepler ...

, was found to be unusually teardrop-shaped, which causes the star to pulsate only on one side, the first known heartbeat star to do so.

Orbital information

Discoveries

References

Further reading