Binary Stars Build Dark Matter Molecules ✛

Original: "Ultralight Boson Ionization from Comparable-Mass Binary Black Holes"

· Yuhao Guo, Zhen Zhong, Yifan Chen, Vitor Cardoso, Taishi Ikeda, Lihang Zhou

arXiv:2509.09643 · 2025-09-11 · CC BY 4.0 · 1 min

General Relativity Cosmology High Energy HEP Phenomenology

Two swirling stars gather dark matter into a giant cloud that resembles a molecule.

A pair of stars whirling in elongated orbits acts like a giant nucleus, and the cloud of dark matter around them, like an electron cloud in a molecule. This 'gravitational molecule' stretches billions of kilometers — more than from the Sun to Pluto. Its size is determined by an analog of the Niels Bohr radius, familiar from the hydrogen atom.

The motion of the stars shakes this cloud, ripping particles out of it — a process similar to atomic ionization. Due to the loss of particles, the pair's orbit gradually rounds: the ellipse becomes a circle. Notably, in the early stages, this effect can surpass the emission of gravitational waves, leaving a characteristic kink in their background.

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The radius of such a 'gravitational molecule' can exceed the distance from the Sun to Pluto, even though the very concept of a radius comes from the microworld.

\frac{da}{dt}\bigg|_{\rm ion} \approx -\frac{8M_g}{M} \alpha \tilde{a}^{1/2} \left( \tilde{a}^{13/4} e^2 F_C(\alpha,\tilde{a}) + 2\times 10^{-3} \tilde{a}^{9/4} F_{/C}(\alpha,\tilde{a}) \right)

Ionization shrinks the orbit; the co-rotating part contributes proportionally to the square of eccentricity, while the non-co-rotating part is nearly constant.

f_t \approx 2.8\, {\rm nHz} \left( \frac{M_g/M}{0.1} \right)^{0.26} \left( \frac{\alpha}{0.05} \right)^{1.7} \left( \frac{10^{10} M_\odot}{M} \right)

The frequency at which ionization ceases to dominate over gravitational waves; depends on the cloud mass and coupling constant.

Scientists

Albert Einstein Barry Barish Kip Thorne Richard Feynman Russell Hulse Stephen Hawking

Concepts

black hole binary interaction eccentric binary gravitational waves ionization ultralight dark matter orbital motion Reionization molecular vibration gravitational wave echoes common envelope bose einstein condensate dark matter boson star black hole dynamics boson ultracold atoms brownian motion polariton bubble collision organic molecules in space ionized carbon neutron star oscillations

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Binary Stars Build Dark Matter Molecules ✛