A Pair of Stars with the Shortest Known Orbital Period

The Optical Gravitational Lensing Experiment (OGLE) is a long-term photometric survey of the sky. Soszynski et al. (2015) present 242 ultra-short-period eclipsing and ellipsoidal binary stars identified in the OGLE field-of-view. One eclipsing binary system, identified as OGLE-BLG-ECL-000066, has an orbital period of less than 0.1 days. This binary system likely consists of a pair of red dwarf stars orbiting one another in a near-contact configuration. The red dwarf stars are each estimated to have ~1/5 the mass and ~1/4 the radius of the Sun.

Nevertheless, more observations will still be required to confirm the status of OGLE-BLG-ECL-000066. If confirmed, OGLE-BLG-ECL-000066 will probably be the shortest-period known binary system with non-degenerate components. The phrase “non-degenerate components” means that the system is not associated with objects such as white dwarf stars, neutron stars and black holes. A pair of red dwarf stars can have an orbital period of less than 0.1 days because red dwarf stars are small and compact, allowing them to be in very close proximity to one another without merging.

Reference:
Soszynski et al. (2015), “Ultra-Short-Period Binary Systems in the OGLE Fields Toward the Galactic Bulge”, arXiv:1503.02080 [astro-ph.SR]