First Oval Orbit Discovered in Black Hole-Neutron Star Collision

A Cosmic First: Oval Orbit Defies Expectations

An international team of scientists has uncovered the first definitive evidence that a black hole and neutron star orbited each other in an oval shape before crashing together, upending decades of assumptions about how these violent cosmic mergers unfold.

The discovery, published on the eleventh of March twenty twenty-six in The Astrophysical Journal Letters, centres on a gravitational-wave event known as GW200105, originally detected by the LIGO and Virgo observatories in January twenty twenty-one.

Rewriting the Textbooks

Researchers from the University of Birmingham, the Universidad Autonoma de Madrid, and the Max Planck Institute for Gravitational Physics applied a novel waveform model that simultaneously accounts for orbital eccentricity and spin-induced precession. Their analysis revealed a median orbital eccentricity of roughly zero point one four five, far from the near-zero circular orbit predicted by standard theory. A circular orbit was ruled out with 99.5% confidence.

Previous analyses had assumed a circular orbit, which led to biased mass estimates. The corrected values place the black hole at roughly thirteen times the mass of the Sun and revise the neutron star mass downward.

What It Means for Astrophysics

The finding suggests that at least some neutron star-black hole pairs form through dynamic gravitational encounters in dense stellar environments, such as globular clusters or galactic nuclei, rather than through the quiet, isolated evolution of a single pair of stars. The oval orbit points to a turbulent origin shaped by gravitational interactions with other stars or possibly a third companion.

An independent analysis using a different waveform model has corroborated the findings, while other known neutron star-black hole mergers appear consistent with circular orbits, making GW200105 a genuine outlier that opens new questions about the diversity of cosmic merger pathways.