Fading Black Hole Flares: The Key Is the Star's Rapid Spin ✦

Original: "The Role of Stellar Spin in Repeating Partial Tidal Disruption Events"

· Ananya Bandopadhyay, Benjamin Amend, Eric R. Coughlin, C. J. Nixon, Dheeraj R. Pasham, T. Wevers

arXiv:2606.02692v1 · 2026-06-01 · CC BY-SA 4.0 · ⏱ 1 min · High Energy

When a star caught in the embrace of a supermassive black hole is initially spinning rapidly in the same direction, tidal forces are powerless to spin it up further, and each new rendezvous ends with an ever dimmer flare.

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Discovery: The mystery of fading flares in repeating TDEs is solved—it's all due to the star's rapid spin. Picture a figure skater: if she’s already spinning like a top, an extra push is useless. Similarly, a star that starts out rotating in sync with its orbital motion doesn't give more and more material to the black hole—its fire fades from one encounter to the next. Now we know that this is a signature of birth via the Hills mechanism: one star in a pair is captured, the other is flung away forever. Soon JWST and LSST will uncover hundreds of these dancing ghosts.

🎯 In a single close pass, the star loses only a fraction of a percent of its mass, but that’s enough to outshine an entire galaxy for months—a pinch of stellar stuff eclipses the light of hundreds of billions of suns.

r_t = R_* \left(\frac{M_\bullet}{M_*}\right)^{1/3}

The distance at which the black hole's tidal forces equal the star's self-gravity. Here R_* and M_* are the star's radius and mass, M_\bullet is the black hole mass.

\Omega_p = \sqrt{ \frac{(1+e)G M_\bullet}{r_p^3} }

The characteristic frequency of matter orbiting the black hole at the pericenter distance r_p. If the star's spin is close to this frequency, the tidal torque is barely transmitted.

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Fading Black Hole Flares: The Key Is the Star's Rapid Spin ✦