Rapid stellar rotation explains fading black hole flares

Astrophysicists have identified a potential solution to a long-standing mystery regarding why certain repeating partial tidal disruption events (rpTDEs) produce flares that grow progressively dimmer with each encounter. Research led by Syracuse University doctoral student Ananya Bandopadhyay, published in The Astrophysical Journal, suggests that a star's rapid rotation prior to its first encounter with a supermassive black hole is the key factor.

In these events, a star passes close enough to a black hole to lose part of its mass without being completely destroyed, allowing the stellar core to remain in orbit and return for subsequent passes. While some systems produce consistent flares, approximately 40% of identified repeating systems show a steady decline in brightness.

Hydrodynamical simulations indicate that rapid stellar spin limits the amount of additional rotation a black hole can add to the star during each encounter, thereby explaining the fading light. The researchers suggest that the high initial rotation may be caused by the breakup of a tight binary star system, which also serves to trap the star in its orbit near the black hole.