BE Lyncis: A Pulsating Star in the Most Eccentric Binary with a Massive Unseen Companion
Year: 2026
Type: article
Abstract: We report the discovery of an exceptionally eccentric binary system, BE Lyncis (BE Lyn), which might host a compact companion with mass ≳2.5 M ⊙ . By combining TESS photometry with an extensive set of times of maximum light spanning 39 yr, we identify BE Lyn as a high-amplitude δ Scuti star in a binary with an orbital period of ≈15.9 yr and an extraordinary eccentricity of e = 0.998 9 − 0.0021 + 0.0008 (>0.9968 at 95% confidence)—the most extreme eccentricity reliably measured for any binary system. Dynamical constraints limit the orbital inclination to i ≲ 10 . ° 1, implying a companion mass M 2 ≳ 2.5 M ⊙ , which identifies the companion as a compact object. This mass points to it most likely being a black hole; if instead it is a rapidly rotating neutron star, it would be the most massive known. If the black hole interpretation holds, it would be the closest such object to Earth. This system provides a unique laboratory for studying asteroseismology in strong gravitational fields, as well as the formation and evolution of extremely eccentric binaries. Our work demonstrates the use of the light-travel time effect in a pulsating star to reveal a compact companion, offering a novel method for detecting black holes in noninteracting binaries.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
OpenAlex ID: W7154753486