Tidal disruption event

A black hole's gravitational attraction changes sharply with distance. If a star approaches sufficiently closely, the near side is pulled more strongly than the far side, stretching the star into streams of gas. The outcome depends on the encounter: a star may be disrupted outside the black hole's event horizon, or in some circumstances may pass through the horizon without producing an observable flare. The term tidal disruption event is commonly used for the observable stellar-disruption phenomenon.

After disruption, debris follows a range of trajectories. Some material can escape the system, while some remains gravitationally bound and returns toward the black hole. Interactions among returning streams can help produce an accretion flow. As gas moves inward, gravitational energy is converted into heat and radiation; the resulting emission can make a galactic nucleus brighten across parts of the electromagnetic spectrum. The detailed light curve and spectrum vary between events, so a bright transient alone is not enough to identify a TDE: astronomers compare its evolution and host galaxy with other possible causes.

TDE flares can reveal a massive black hole in a galaxy whose nucleus is otherwise faint. Their brightness, spectra and changes over time provide evidence about the disrupted star, the debris and the surrounding environment, although interpretations can be model-dependent. In a small number of events, observations have also raised the possibility of high-energy particle production. NASA describes the event AT2019dsg, discovered in 2019, as being associated on the sky with the high-energy neutrino IC191001A; that association prompted questions about how and when such neutrinos might be produced, rather than resolving the mechanism.

Because a TDE changes with time and can occur in otherwise quiet galaxies, wide-field surveys that repeatedly image the sky are important for discovery. Follow-up observations at different wavelengths help determine whether a new flare is consistent with stellar disruption and track how it evolves. Rubin Observatory notes that repeated, wide-area observations are expected to increase the number of TDE candidates available for study. Such surveys expand the sample, but the expected yield is a forecast rather than a count of already confirmed events.