Papers Clash Over Whether BE Lyncis Hides a Nearby Black Hole

A pair of newly accepted astronomy papers has turned the pulsating star BE Lyncis into a live scientific dispute, not a settled black-hole discovery.

One paper, accepted to The Astrophysical Journal Letters, argues that BE Lyncis may be orbiting a massive unseen companion in an extraordinarily stretched 15.9-year orbit. The authors say the companion is most likely a black hole. But a second paper, accepted to Publications of the Astronomical Society of the Pacific, says the star’s motion on the sky as measured by Gaia and Hipparcos does not fit that picture.

That clash matters because, if the first interpretation is right, BE Lyncis would be an unusually nearby dormant black-hole candidate and, according to that team, would sit in the most extreme binary orbit reliably measured. For now, though, the evidence from two standard methods points in different directions.

The black-hole case comes from Jia-Shu Niu, Ying Zhang and Hui-Fang Xue in a paper titled “BE Lyncis: A Pulsating Star in the Most Eccentric Binary with a Massive Unseen Companion,” posted on arXiv as 2601.12999 and marked as accepted to The Astrophysical Journal Letters. The latest arXiv version, v4, was posted June 18.

BE Lyncis, or BE Lyn, is a high-amplitude Delta Scuti star, meaning it regularly brightens and dims as it pulsates. Niu and colleagues treated those pulsations like a clock. They combined TESS observations with 445 recorded times of maximum light spanning 39 years, from 1986 to 2025, and modeled slight shifts in when the pulses arrived.

From that timing analysis, they inferred an orbit with a period of about 15.9 years and an eccentricity of 0.9989, with the paper saying the value is greater than 0.9968 at 95% confidence. In the abstract, the authors wrote: “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⊙.”

In the current version of the paper, they say dynamical constraints limit the orbital inclination to 10.1 degrees or less. That, in turn, implies a companion mass of at least 2.5 times the mass of the sun. The paper argues that such an unseen object would have to be compact and is most likely a black hole, though a very massive neutron star is not fully ruled out. The authors place the system at about 250 parsecs from Earth and say that, if the black-hole interpretation holds up, it would be the nearest known black hole.

They also present the method itself as part of the significance. “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 abstract says.

The rebuttal comes from Pranav Nagarajan, Kareem El-Badry, Thomas J. Maccarone and co-authors in a paper titled “BE Lyncis is not a Black Hole Binary: Lessons From Gaia and Hipparcos Astrometry,” posted on arXiv as 2601.22071 and listed as accepted to PASP.

Their core argument is that a nearby star in a wide orbit around a heavy dark companion should usually show a clear astrometric signal — a measurable wobble or mismatch in its motion across the sky. They say BE Lyncis does not.

First, the team examined the star’s proper-motion anomaly, which compares motion measured by the Hipparcos mission in the 1990s with Gaia’s later measurements. They report an observed anomaly of about 1.7 plus or minus 0.8 milliarcseconds per year. By contrast, their paper says the proposed black-hole orbit would predict a signal at least 10 times larger. As the abstract puts it: “We find that the predicted PMA is at least an order of magnitude larger than the observed value of ≈1.7 ± 0.8 mas yr−1.”

Second, they point to Gaia’s RUWE value, a standard quality indicator that can rise when a source’s motion is not well fit by a single-star model. Nagarajan and colleagues say the proposed orbit should produce a Gaia RUWE of roughly 2.5 to 4.0, while the observed Gaia DR3 value is 1.073. “The observed value is instead consistent with a low-mass secondary or a single star,” their abstract says.

The timing and astrometry papers are not perfectly synchronized: the astrometric rebuttal was written in response to Niu and colleagues’ initial January preprint, and the timing paper was revised several times through June. But the newest version still argues for an ultra-eccentric orbit and a companion above 2.5 solar masses, so the central conflict remains.

In plain terms, the first team says BE Lyn’s pulsations arrive a little early and a little late because the star is moving around an unseen object, changing how far the light has to travel. The second team says that if such a massive companion were really there, Gaia and the long Hipparcos-to-Gaia baseline should already show it. Recent dormant-black-hole claims have generally needed multiple independent methods to line up before winning broad acceptance.

For now, BE Lyncis looks less like a confirmed nearby black hole than a test case in how competing techniques can disagree. Both papers point to the same next steps: radial-velocity measurements and future Gaia data releases should provide the clearest way to decide which picture is right.