main concepts scientists sections
SimplePopularAdvanced

A Black Hole's Double Rhythm: NICER Sees Ansky's Flares Slow Down by Half ✛

Original: "NICER observations reveal doubled timescales in Ansky's quasi-periodic eruptions (QPEs)"
· L. Hernández-García, P. Sánchez-Sáez, J. Chakraborty, J. Cuadra, G. Miniutti, R. Arcodia, P. Arévalo, M. Giustini, E. Kara, C. Ricci, D. R. Pasham, Z. Arzoumanian, K. Gendreau, P. Lira
arXiv:2509.16304 · 2025-09-19 · CC BY 4.0 · 3 min
High Energy Galaxies
In 2025, Ansky's quasi-periodic eruptions became twice as rare, twice as long, and four times more energetic than a year earlier.

Context

Quasi-periodic eruptions (QPEs) are repeating X-ray bursts from the vicinity of supermassive black holes. Their nature remains debated: models fall into accretion disk instabilities and interactions with an orbital companion in an extreme-mass-ratio inspiral (EMRI) system. Ansky is the brightest known QPE source, ten times brighter than any other, making it an ideal laboratory for testing models. The work builds on a body of neighboring studies that have already examined eruption rhythms and their connection to tidal disruption events.

Methods

From January to June 2025, the NICER instrument aboard the ISS accumulated 283 kiloseconds of observations of Ansky in 213 separate sessions. X-ray spectra were processed with a time resolution of 200 seconds, and background was subtracted using a method described in previous work by the team. Light curves were fitted with a model of exponential rise and decay, from which peak times, durations, and total eruption energies were extracted. Temperatures and bolometric luminosities were estimated using a blackbody model.

Results

In 2025, 14 eruptions were recorded with a mean interval between peaks of 907±25 kiloseconds (~10.5 days) and a mean duration of 243±35 kiloseconds (~2.8 days). This is twice as long as in 2024, when the interval was 436.8±80.3 kiloseconds and the duration 129±43.2 kiloseconds. The total radiated energy per eruption quadrupled, from roughly 1×$10^{48}$ erg in 2024 to (3.98±0.4)×$10^{48}$ erg in 2025. The rise time barely changed (0.84±0.06 days versus 0.81±0.08), while the decay time doubled: 2.23±0.15 days versus 1.28±0.10. Within the 2025 season, the interval between eruptions systematically increases at a rate of ~0.1 days per eruption, corresponding to a period derivative of ~+$10^{-2}$. On the duration–period diagram, Ansky still follows the general power-law relation for QPEs, but has shifted to longer timescales.

Implications

The rapid doubling of the period and the increase in energy over six months challenge models where the period is set by the companion's orbit: an orbit cannot change that quickly. The proposed scenario, involving a transition from two-sided shocks (when debris punches through the disk) to one-sided shocks (when debris does not), explains the period doubling without changing the orbit. This is the first observational hint of evolution in the emission mechanism of QPEs. This work differs from neighboring studies in that it captures not just the presence of eruptions, but their evolution over time, and offers a specific testable scenario.

Future development

If the proposed scenario is correct, Ansky's period should stabilize around 10 days, although rapid switching between 5 and 10 days is possible. Numerical simulations of stellar ablation and disk evolution will allow a quantitative test of the picture. Future observations with NICER and XMM-Newton, already approved, will continue to track the period and shape of the eruptions. Detecting period doubling in other long-period QPEs would be a smoking gun for the collision scenario.

Impact

The results directly affect models of EMRIs and accretion disks, as well as strategies for finding electromagnetic counterparts of gravitational-wave sources for future missions like LISA and TianQin.

Next steps

Continue monitoring Ansky with NICER and XMM-Newton to check for period stabilization. Conduct hydrodynamic simulations of debris–disk interactions to reproduce the observed energies and profiles.

Key open problems

For accretion physics, the question remains open which mechanism, disk instabilities or collisions with a companion, dominates in QPEs. This work shows that the evolution of a source over time could be a key test: models must explain not only average parameters but also their rapid changes.

The knowledge machine's view

This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.

What the work does

The study reports new NICER observations of quasi-periodic eruptions (QPEs) in the nucleus of the galaxy Ansky. In 2025, the eruption period doubled compared to 2024, the duration increased, and the total energy rose by a factor of four. The authors propose a scenario in which the change is linked to a transition from two-sided to one-sided shock waves when a companion collides with the disk.

Where its strength is

The strength of the work lies in documenting the evolution of the QPE rhythm over time and proposing a concrete, testable mechanism that ties the period change to the shock geometry. This opens the way to testing models of companion–disk interactions.

Where it could go next

Worth trying

  • Try applying the model from the paper about the arrow piercing the disk to the Ansky data to estimate the companion and disk parameters.
  • Check whether the observed evolution of duration and energy is consistent with the predictions of the double-flare model.
  • Assess the possible contribution of black hole spin to the rhythm change, using the approach from the plate paper.

Why this may matter

Such QPE evolution could be key to understanding the eruption mechanism and the interaction of compact objects with accretion disks in galactic nuclei.

Nearby works in our archive

The closest work in the archive sits at 0.66 by meaning — the usual level for our corpus.

Whole graph →

Ansky is the brightest known QPE source: its peak luminosity reaches 2×$10^{43}$ erg/s, ten times brighter than any other. Yet in 2020–2023 it showed no X-ray emission at all; the eruptions only began after an optical flare in 2019.

F_{\mathrm{QPE}} = \begin{cases} A\lambda e^{\tau_1/(t_{\mathrm{peak}}-t_{\mathrm{as}}-t)} & t < t_{\mathrm{peak}} \\ A e^{-(t-t_{\mathrm{peak}})/\tau_2} & t \ge t_{\mathrm{peak}} \end{cases}
A is the amplitude, τ1 and τ2 are the exponential rise and decay times, λ is a normalization, and tas is the asymptotic time
R_{\mathrm{bb}} = \sqrt{\frac{L_{\mathrm{bol}}}{4\pi\sigma_{\mathrm{SB}} T^4}}
Rbb is the blackbody radius, Lbol is the bolometric luminosity, T is the temperature, and σSB is the Stefan-Boltzmann constant

Key numbers

  • 2024 eruption period: ~4.5 days
  • 2025 eruption period: ~10 days
  • 2025 eruption energy: (3.98±0.4)×1048 erg
  • energy increase: 4 times
  • period increase rate: ~0.1 days per eruption
Concepts
quasi periodic eruptions black hole activity cycles quasi biennial oscillation changing agn activity quasar feedback blazar flare starburst microquasar active galactic nucleus quasar tidal disruption event black hole outburst