Astronomers studying repeating partial tidal disruption events (rpTDEs) have discovered why certain black hole flares grow steadily fainter over time rather than maintaining peak brightness. According to research published in The Astrophysical Journal by astrophysicists at Syracuse University, a star’s rotation rate prior to its first close encounter with a supermassive black hole dictates how its debris behaves during subsequent passes.
How Supermassive Black Holes Shred Stars Incrementally
Most galaxies harbor a supermassive black hole at their center with a mass millions or billions of times greater than the Sun. When a star ventures too close, standard tidal disruption events completely tear the stellar body apart, creating an accretion disc that emits bright flares over days to months. However, partial tidal disruption events allow a star’s core to survive an initial close pass. According to Syracuse University researchers, the surviving stellar remnant loops back in an eccentric orbit to shed more material during subsequent encounters spaced months or years apart.
The Mystery of Fading Flares in Repeating Systems
Astronomers have identified roughly 10 repeating partial tidal disruption systems to date, and four of those systems display flares that become progressively dimmer with each return. Previous hydrodynamical simulations struggled to explain this cooling behavior, consistently predicting that smaller amounts of stripped material would still yield flares of comparable peak brightness. Doctoral student Ananya Bandopadhyay, working alongside postdoctoral researcher Benjamin Amend and associate professor Eric Coughlin in the Syracuse University Department of Physics, investigated why these models fell short.
The team discovered that a star’s spin rate before its initial encounter plays a critical role in framing how the stellar core responds to repeated gravitational stress. While low-mass stars behave like fluffy meringues that become increasingly susceptible to tidal forces, higher-mass stars feature onion-like internal structures with concentrated matter at the center. Tidal forces do not just strip mass; they also apply torque that spins the star up faster before subsequent periapse passages, altering the mass-loss trajectory and dimming the resulting electromagnetic flares over time.
Frequently Asked Questions
What is a repeating partial tidal disruption event?
A repeating partial tidal disruption event occurs when a star passes close enough to a supermassive black hole to lose outer layers of mass without being completely destroyed, leaving a surviving core that returns on an orbit for repeated encounters.
Why do some black hole flares get dimmer?
According to Syracuse University researchers publishing in The Astrophysical Journal, the pre-encounter spin rate of the star and the tidal torque applied during close passes alter how much material is stripped away during subsequent orbits, reducing flare brightness over time.
How many repeating systems have astronomers found?
Astronomers have identified approximately 10 repeating partial tidal disruption systems, with four of those displaying progressively fainter flares on each return.
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