For 39 years, astronomers have been recording how the star BE Lyn brightens and dims. Its light pulsates with a rhythm of several hours, like a lighthouse that never stops blinking. But there is a glitch in this rhythm: sometimes the flashes came a little early, sometimes a little late. The star was moving closer to Earth and then farther away, as if something were dragging it in a circle.
It turns out that BE Lyn is not alone. An invisible companion orbits around it, and the orbit of this pair is stretched to the limit. At the farthest point, the distance between them is hundreds of times greater than at the closest point. For comparison, Earth's orbit is almost circular, but here it is like a highly squashed oval. When the star whips past its companion, its pulse noticeably speeds up.
The companion is heavy — at least 2.5 solar masses, but no light is seen from it. Such a massive yet dark object is most likely a black hole. If confirmed, it would be the closest known to Earth. Astronomers have a rare opportunity to study how strong gravity affects a star's rhythm, and possibly to discover a new way to find black holes that reveal themselves only through gravity.
as written by the authors arXiv:2601.12999
We report the discovery of an exceptionally eccentric binary system, BE Lyncis (BE Lyn), which might host a compact companion with mass $$\gtrsim 2.5~M_{\odot}$$. By combining TESS photometry with an extensive set of times of maximum light spanning 39 years, we identify BE Lyn as a high-amplitude $$\delta$$ Scuti star in a binary with an orbital period of $$\approx15.9$$ years and an extraordinary eccentricity of $$e=0.9989^{+0.0008}_{-0.0021}$$ ($$>0.9968$$ at 95% confidence) -- the most extreme eccentricity reliably measured for any binary system. Dynamical constraints limit the orbital inclination to $$i \lesssim 10^{\circ}.1$$, implying a companion mass $$M_2 \gtrsim 2.5~M_{\odot}$$, 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.
The pulse of BE Lyn is off by only a few seconds over 39 years of observations, but that was enough to suspect a black hole.
In the movie 'Interstellar,' the heroes travel to the black hole Gargantua; BE Lyn might harbor a similar object, but much closer — within our galaxy.