How do black holes affect neighboring stars?

Black holes shape the motions and fates of nearby stars primarily through gravity and energetic feedback. In galactic nuclei, the dominant gravitational field of a supermassive black hole organizes the orbits of surrounding stars into tightly bound trajectories, chaotic scatterings, or direct capture. Long-term astrometric monitoring by Andrea Ghez at University of California Los Angeles and Reinhard Genzel at Max Planck Institute for Extraterrestrial Physics demonstrated that compact massive objects at the centers of galaxies control the kinematics of so-called S-stars, providing direct evidence of how black hole gravity governs stellar dynamics in dense environments.

Tidal forces and stellar disruption

When a star ventures too close, differential gravity can overcome the star’s self-gravity and tear it apart in a tidal disruption event. Observational campaigns led by Suvi Gezari at University of Maryland have cataloged luminous flares consistent with stellar disruption and subsequent accretion onto a black hole, using ultraviolet and X-ray facilities. These transients convert a fraction of a star’s mass into high-energy radiation, temporarily outshining the host nucleus and supplying fresh material to the black hole. The same gravitational interactions that create tidal disruptions can also eject one member of a disrupted binary system as a hypervelocity star. Jack G. Hills at Los Alamos National Laboratory first described this ejection mechanism, and follow-up surveys by Warren Brown at Harvard Smithsonian Center for Astrophysics have identified stars traveling fast enough to escape their galaxies, testifying to the black hole’s role in reshaping stellar populations.

Accretion, jets, and galactic feedback

Material drawn from a star or the surrounding interstellar medium forms an accretion disk that radiates across the electromagnetic spectrum and can launch relativistic jets. Andrew Fabian at University of Cambridge and colleagues have analyzed X-ray images that reveal cavities and shocks in hot gas around active nuclei, demonstrating that black hole outflows deposit energy into their environment. This feedback modifies the thermal state and pressure of surrounding gas, which can suppress star formation by preventing gas from cooling or, in some cases, trigger star formation by compressing clouds. The scale and sign of these effects depend on the host galaxy’s mass, gas content, and the timing of outbursts, producing different evolutionary outcomes in massive ellipticals, spiral nuclei, and dwarf systems.

Mergers and long-term consequences

Interactions between black holes and stars also have enduring structural consequences. Repeated scattering and capture change central stellar density profiles and can create cores or cusps in galactic centers. Mergers of stellar-mass black holes, often the endpoint of compact object interactions, produce gravitational waves measured by the LIGO Scientific Collaboration at California Institute of Technology and Massachusetts Institute of Technology, confirming that close dynamical encounters lead to relativistic mergers. Observational work comes from a global network of observatories and institutions, reflecting the international collaboration needed to trace how black holes influence their stellar neighborhoods. Overall, through orbital shaping, violent tidal disruption, energetic feedback, and occasional ejection of stars, black holes act as catalysts of dynamical and evolutionary change in their local stellar ecosystems.