A tidal disruption event has shown transitions between X-ray states that until now were described only for black hole binary systems.
Event 2025aarm is a tidal disruption (when a star passes too close to a black hole and is torn apart by its gravity). It is the second closest known case of its kind. Its proximity, together with a six-month monitoring campaign, let astronomers track the source down to a luminosity of about 7×10³⁹ erg/s in the 0.2–10 keV band near the optical peak. This is the faintest X-ray emission recorded in the early stage of such an event.
After the first detection, the source brightened by nearly a factor of a hundred. The peak X-ray luminosity — about 5×10⁴¹ erg/s — came roughly four months after the optical peak.
Spectral analysis revealed an unusual sequence. At first the emission was hard and dominated by a power law. Then, as the luminosity rose, it grew softer and was dominated by an accretion disk. Later the spectrum hardened again. Such "low-hard to high-soft" transitions are well known in black hole binaries, but had not been described for thermal tidal disruptions before. The authors explain this by changing contributions of the accretion disk and a corona that scatters the emission.
The extremely faint early emission supports the idea that the split of these events into "X-ray bright" and "undetected" is largely a selection effect, depending on the depth and cadence of observations. The event itself hints at a possible universality of accretion across a wide range of black hole masses.