Black Hole Throws Off Its Rhythm express
Astronomers are monitoring X-ray flares from the vicinity of a black hole at the center of a galaxy. These flares repeat with a certain rhythm, like heartbeats. Normally, as a star approaches a black hole, the rhythm speeds up — just as a pulse quickens when running. But at the black hole 'Ansky,' the rhythm is slowing down. Each successive beat lags more than the previous one: over a day, the gap grows by almost half an hour. It's as if the heart, instead of racing under stress, were slowing to a halt.
Nobody yet knows why this rhythm is slowing. Perhaps we're missing some fundamental process — for instance, an unknown way of losing energy.
Original abstract
as written by the authors arXiv:2602.16776
We report the first direct measurement of the period derivative in a quasi-periodic eruption (QPE), finding a smoothly increasing period with $$\dot{P}\approx (1.7\pm 0.02)\times10^{-2}$$ d d$$^{-1}$$ in the source ZTF19acnskyy/"Ansky". Most models for QPEs invoke repeated interactions of a stellar-mass orbiting companion around the supermassive black hole (SMBH) in an extreme mass-ratio inspiral (EMRI). In these scenarios, a positive $$\dot{P}$$ is surprising, but not impossible to produce. We explore several possible explanations for the observed $$\dot{P}$$, including stable mass-transfer driven by impulsive mass loss events in an EMRI, velocity kicks at pericenter due to tidal interactions with the SMBH, apparent period changes due either to general relativistic precession effects in an EMRI or light travel-time delays in a hierarchical SMBH binary, and mass-transfer variations in a thermal/viscous disk instability model. We find that none of the considered models provides a complete explanation for the data, motivating further work on physical explanations for positive period derivatives in QPEs.
Each flare lasts several hours, while the intervals between them can span months. The change in tempo has been measured with jeweler's precision: 0.017 days per day — roughly 24 minutes of daily lag.