• DOI:10.1126/science.1251999
• Corpus ID: 10399983

KOI-3278: A Self-Lensing Binary Star System

@article{Kruse2014KOI3278AS,
  title={KOI-3278: A Self-Lensing Binary Star System},
  author={Ethan Kruse and Eric Agol},
  journal={Science},
  year={2014},
  volume={344},
  pages={275 - 277}
}

• E. Kruse, E. Agol
• Published 16 April 2014
• Physics, Geology
• Science

Starry Brightness The high photometric precision of NASA's Kepler observatory has enabled the detection of many planets because they cause slight dimming of their host stars as they orbit in front of them. From these data, Quintana et al. (p. 277) have spotted a five-planet system around a small star. Here, the outermost planet is only 10% larger than Earth and completes its 130-day orbit entirely within the habitable zone, where liquid water could exist on its surface. Similarly, Kepler can detect faint periodic brightenings, as Kruse and Agol (p. 275) have reported for the binary system KOI-3278. In this system, a white dwarf acts as a gravitational microlens when it passes in front of its Sun-like G-star companion every 88 days. The lensing effect allows the mass of the white dwarf to be estimated, which helps us to understand how similar binary systems may have evolved. A white dwarf that eclipses a Sun-like star enhances, rather than dims, its brightness through relativistic effects. Over 40% of Sun-like stars are bound in binary or multistar systems. Stellar remnants in edge-on binary systems can gravitationally magnify their companions, as predicted 40 years ago. By using data from the Kepler spacecraft, we report the detection of such a “self-lensing” system, in which a 5-hour pulse of 0.1% amplitude occurs every orbital period. The white dwarf stellar remnant and its Sun-like companion orbit one another every 88.18 days, a long period for a white dwarf–eclipsing binary. By modeling the pulse as gravitational magnification (microlensing) along with Kepler’s laws and stellar models, we constrain the mass of the white dwarf to be ~63% of the mass of our Sun. Further study of this system, and any others discovered like it, will help to constrain the physics of white dwarfs and binary star evolution.