Fifty new stellar systems show their brightness varying in a pattern reminiscent of the regular pulses of a heart.
These objects are not solitary stars. Each one consists of two stars orbiting each other on a highly elongated orbit. They therefore spend much of their journey relatively far apart, then come very close together at regular intervals. It is during this close passage that their light changes in a characteristic way.
Artist’s view of a “heartbeat star” system during its close passage on a highly elongated orbit.
Credit: NASA/JPL-Caltech
The gravity of each star then pulls more strongly on its companion. The two stars may become slightly distorted, changing the amount of light received from Earth, and oscillations may also be triggered inside the stars. On a graph showing their brightness over time, the combination produces a shape reminiscent of a heartbeat.
Astronomers therefore refer to them as “heartbeat stars,” even though there is obviously no heart in these systems. To identify new examples, the team combined two types of measurements. The TESS space telescope tracked changes in brightness. The APOGEE survey provided measurements of the stars’ motion through their light.
This combination made it possible to identify 50 systems. The researchers then fitted their observations with a model describing the expected change in light. They used it to estimate several properties of the orbits, including their period, highly elongated shape, and orientation relative to Earth.
For some systems with enough APOGEE measurements, the team can also obtain information about the companion star’s mass. These data make it possible to study what happens when two stars periodically approach each other without necessarily coming into contact.
The significance goes beyond simply searching for unusual objects. Gravity-induced distortions can set stellar matter in motion: by observing the resulting oscillations, astronomers have an indirect way to study the interior of a star, which is normally hidden from view.
The new sample now provides 50 additional targets for more precisely measuring the effect of repeated close passages. Extended observations may refine the masses and orbits, then link these parameters to the oscillations observed in each star.