Astronomers studying repeating partial tidal disruption events have discovered that rapidly spinning stars can explain why some black hole flares mysteriously grow dimmer over time. Meanwhile, separate observations of the Milky Way’s supermassive black hole reveal that objects like the G2 dust cloud and binary star system D9 are surviving close encounters intact.
Solving the Fading Flare Mystery in Repeating Tidal Disruptions
When a star passes dangerously close to a supermassive black hole, the gravitational pull can tear it apart in a dramatic display known as a tidal disruption event. But destruction is not always immediate. In repeating partial tidal disruption events, or rpTDEs, a star sheds only its outer layers and survives, returning for repeated close passes that generate fresh bursts of light months or years apart. Wide-field time-domain surveys have helped astronomers track these recurring systems, identifying roughly 10 repeating candidates so far, including ASASSN-14ko, AT2018fyk, eRASSt-J045650, AT2022dbl, AT2020vdq, AT2021aeuk, and AT2023uqm.
Yet four of these repeating systems presented researchers with a persistent puzzle: instead of producing steady or brightening flares, their emissions grew progressively dimmer with each return. Earlier hydrodynamical simulations struggled to replicate this fading behavior, consistently predicting flares of roughly the same peak brightness even as the star lost less material during each successive passage.
To resolve the discrepancy, researchers at Syracuse University investigated the role of stellar rotation before the initial encounter. Led by doctoral student Ananya Bandopadhyay alongside Benjamin Amend and Eric Coughlin, the team published findings in The Astrophysical Journal showing that a star already spinning rapidly before its first close approach experiences much less additional spin-up from the black hole. With the rotation rate remaining relatively steady, the fallback timescale of the stripped debris does not accelerate, allowing the peak fallback rate to decline as the dense surviving core sheds progressively less mass over time.
New Observations Reveal the Milky Way’s Black Hole Preserves Rather Than Destroys
While distant black holes shred stars into repeating streams of gas, the supermassive black hole at the center of our own galaxy appears remarkably restrained. Using the Enhanced Resolution Imager and Spectrograph on the Very Large Telescope in Chile, an international research team led by PD Dr. Florian Peißker at the University of Cologne tracked peculiar dusty objects near Sagittarius A* and published their results in Scitechdaily.
The observations directly challenge long-held assumptions that the galactic center acts as a relentless cosmic consumer. For instance, G2 was widely interpreted as an elongated cloud of gas and dust destined to be torn apart by spaghettification. Instead, ERIS data confirm that G2 maintains a stable orbit, strongly suggesting it conceals an intact star. Similarly, D9, a binary star system discovered by Peißker’s team in 2024, continues to survive extreme tidal forces without merging, alongside stable orbital trajectories observed for objects X3 and X7.
Extreme Density and the Physics of Spaghettification
The stark difference between a star surviving a close flyby and being completely obliterated comes down to mass, density, and the fundamental mechanics of tidal forces.
Future discoveries rest on advanced instrumentation.
