In the ever-evolving cosmos, supermassive black holes continue to astonish astronomers with phenomena that challenge existing theories and expand our understanding of accretion physics. Among these phenomena, quasi-periodic eruptions (QPEs) stand out as some of the most intriguing and enigmatic signals emanating from the centers of galaxies. These transient X-ray bursts recur rapidly and with remarkable regularity, hinting at complex interactions between the supermassive black hole and the matter spiraling into its gravitational grasp. Recent observations have now unveiled a new chapter in this cosmic saga, revolving around the galaxy SDSS1335+0728—a galaxy that had for two decades remained a steady and unremarkable beacon in the night sky until a sudden awakening was identified.
For approximately twenty years, the galaxy SDSS1335+0728 exhibited remarkably stable optical emissions, offering little indication of the tumultuous activity hidden at its core. This changed radically in December 2019 when an unexpected increase in optical brightness was observed, signaling the onset of a significant event in the galactic nucleus. Over the subsequent five years, this elevated state persisted, marked by variability in emissions characteristic of an active galactic nucleus (AGN). Such a transformation is emblematic of material suddenly ramping up its accretion onto the central supermassive black hole, estimated to possess a mass on the order of one million solar masses (~10^6 M☉). This “turn-on” AGN phase provided astronomers with a rare opportunity to witness the birth of a new accretion regime in real-time.
The most groundbreaking revelation emerged in early 2024 when X-ray emissions were first detected from SDSS1335+0728. These emissions displayed an extraordinary pattern of quasi-periodic eruptions occurring every approximately 4.5 days. What sets this discovery apart from previously documented QPE sources is the extreme nature of the observed eruptions. The bursts exhibit exceptional brightness peaks and amplitude changes, outlasting many similar bursts documented to date in both intensity and duration. Each eruption releases a substantial amount of energy, integrated over the full burst profile, suggesting highly efficient and sustained accretive processes at work in the immediate environment of the black hole.
Delving into the temporal dynamics, alongside the 4.5-day QPE recurrence, scientists identified a longer superperiod of roughly 25 days overlaying the pattern. This superperiodicity implies a complex underlying physical mechanism modulating the accretion disk or the flow of matter into the black hole. The coexistence of these two distinct temporal scales challenges previous models of QPE production, which predominantly focus on shorter, repeating bursts tied to tidal disruption event aftermaths or instabilities confined to the innermost regions of the accretion disk. The presence of a longer modulation cycle suggests involvement of larger-scale dynamics, possibly hinting at orbital patterns of secondary bodies or warped disk precession affecting the inner accretion environment.
Furthermore, while strong X-ray bursts dominate the observational signature of SDSS1335+0728, subtle ultraviolet (UV) variations have also been reported, albeit at low statistical significance. These UV flux changes are likely tied to the broader accretion flow and originate from larger radii within the disk, where temperatures are cooler and matter transitions from optical/UV emitting regimes to X-ray emitting plasma near the event horizon. The detection of UV variability correlated with the timing of X-ray eruptions, even if marginal, enriches the multi-wavelength portrait of these phenomena and opens new avenues to probe the radial structure and heating processes within the accretion disc.
The discovery casts new light on the formation channels of QPEs. Traditionally, such eruptions have been associated mainly with tidal disruption events (TDEs), where a star wandering too close to a supermassive black hole is torn apart, fueling violent bursts of emission. However, the long, sustained evolution of SDSS1335+0728’s active nucleus and the characteristics of its QPEs suggest a broader paradigm. Rather than an impulsive event with a limited fuel supply, this galaxy exemplifies a scenario where the onset of a new accretion flow—likely stable yet prone to periodic instabilities—generates these powerful X-ray flares. This perspective reconciles the presence of QPEs in post-turn-on AGN, highlighting that they may be a natural byproduct of the establishment or reconfiguration of accretion disks around previously quiescent black holes.
From a theoretical standpoint, the mechanisms giving rise to QPEs remain an active field of inquiry. One prevailing hypothesis involves oscillatory accretion instabilities, possibly driven by disk instabilities such as thermal-viscous cycles or magnetohydrodynamic (MHD) turbulence near the innermost stable circular orbit. Alternatively, some models posit interactions with orbiting stellar or compact objects, whose gravitational influence periodically perturbs the accretion flow, creating episodic enhancement in emission. The dual timescale pattern observed here, with a short burst interval superimposed on a longer modulation period, is particularly suggestive of such two-body effects or disk warping phenomena.
The observational campaign that unveiled these phenomena leveraged state-of-the-art X-ray observatories equipped with high temporal and spectral resolution, complemented by UV monitoring instruments capable of capturing faint signal fluctuations over extended periods. This multi-year, multi-wavelength observation strategy was crucial for identifying both the rapid QPE behavior and its long-term evolutionary context, emphasizing the importance of persistent monitoring in astrophysics. These findings illustrate how black hole feeding processes, thought historically as relatively steady and continuous, can instead exhibit abrupt transitions and cyclic instabilities that impact their energetic output dramatically.
The implications extend beyond mere curiosity and demand re-examination of how black holes grow and how the environments of galactic nuclei transform over humanly observable timescales. The SDSS1335+0728 case argues persuasively that accretion disks can “turn on” suddenly, entering regimes that produce extraordinary flaring activities and complex variability patterns within just a few years. This challenges linear models of black hole growth and suggests galaxies can dynamically switch between dormant and active states, with corresponding impacts on their host environments and evolution.
Moreover, the energy output from these QPEs is substantial enough to affect the surrounding interstellar medium. X-ray illumination from the central black hole can ionize nearby gas clouds, influence star formation rates, and inject turbulence into the galactic core, with potentially profound consequences for galactic ecology. Understanding the timing, amplitude, and longevity of these eruptions helps clarify the feedback mechanisms linking black holes to their host galaxies—a pivotal question in contemporary astrophysics.
Looking forward, SDSS1335+0728 stands as a critical laboratory for testing accretion physics theories. Future observing campaigns focused on refining the timing parameters, improving spectral diagnostics during bursts, and searching for correlated variations across radio, optical, UV, and X-ray bands will provide deeper insights. Similarly, dedicated theoretical and computational modeling efforts simulating accretion disk dynamics under variable feeding conditions will be essential to decode the physical origin of the superperiod and the nature of the modulation in QPE behavior.
The excitement within the astrophysical community surrounding this discovery is palpable. Witnessing the real-time awakening of an AGN and the onset of such extreme and periodic eruptions gives researchers a unique vantage point over dynamic processes otherwise lost in the vast cosmic timescales. This finding extends the known diversity of black hole accretion phenomena and holds the potential to inspire a surge of similar investigations, potentially uncovering more galaxies undergoing comparable transitions and broadening the statistical understanding of quasi-periodic eruption sources.
In conclusion, the detection of extreme QPEs in SDSS1335+0728 marks a significant advance in black hole astrophysics. With record-breaking flux amplitudes, unusually long eruption durations, and a superimposed superperiodic cycle, it challenges prior conceptions about the origins and characteristics of these phenomena. By linking QPEs not only to catastrophic tidal disruptions but to the formation and evolution of new accretion flows in nascent AGN, this discovery enriches our grasp of the complexity and variability inherent in the cosmic engine rooms at galaxy centers. As studies continue, SDSS1335+0728 will undoubtedly remain a focal point for unraveling the mysteries of how supermassive black holes grow, interact, and influence their cosmic surroundings.
Subject of Research:
Extreme quasi-periodic eruptions (QPEs) in a newly accreting supermassive black hole within the galaxy SDSS1335+0728, their temporal properties, energetics, and implications for accretion flow formation and black hole activity.
Article Title:
Discovery of extreme quasi-periodic eruptions in a newly accreting massive black hole
Article References:
Hernández-García, L., Chakraborty, J., Sánchez-Sáez, P. et al. Discovery of extreme quasi-periodic eruptions in a newly accreting massive black hole. Nat Astron (2025). https://doi.org/10.1038/s41550-025-02523-9
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