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Rapid star spin explains fading flares from black hole encounters, study finds

Astrophysicists propose that pre-existing rotation and binary star disruption account for the dimming flashes of light and tight orbits seen in repeating partial tidal disruption events.

Updated Aug 24, 2026 · 00:17 UTC1 reports

The short version

  • Syracuse University astrophysicists published research explaining why light flares from certain stars repeatedly skimmed by supermassive black holes grow progressively dimmer.
  • Hydrodynamic simulations show that stars already spinning rapidly prior to capture experience limited additional tidal spin-up, leading to lower peak fallback rates of debris and fading light bursts.
  • The Hills mechanism, where a tight binary system is split by a black hole's gravity, explains both the initial high spin and the unusually tight orbits observed.
  • Researchers suggest this capture process may also help explain the origins of certain stars orbiting Sagittarius A* at the center of the Milky Way.

Key facts

  • Repeating partial tidal disruption events occur when a star survives close encounters with a supermassive black hole, losing outer mass and producing bursts of light on each pass.[ScienceDaily]
  • About four of the roughly 10 identified repeating partial tidal disruption systems produce flares that become progressively fainter with each return, a pattern prior models could not recreate.[ScienceDaily]
  • New simulations published in The Astrophysical Journal demonstrate that rapid stellar rotation prior to black hole capture keeps fallback times steady as mass loss declines, resulting in dimmer flares.[ScienceDaily]
  • The Hills mechanism provides a theoretical framework explaining how a tidal breakup of a compact binary system yields both a fast-spinning, tidally locked star and a tight orbit lasting only months.[ScienceDaily]

What remains uncertain

  • Whether the Hills mechanism accounts for specific unusual stellar populations orbiting Sagittarius A* in the Milky Way remains an open hypothesis noted by researchers.[ScienceDaily]

Sources