Recoiling Supermassive Black Holes in Our Backyard

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

The collective motion of stars in the cores of galaxies reveals the presence of supermassive black holes, generally millions to billions of times more massive than the Sun. Gravitational waves can deliver a kick to orbiting stars when two supermassive black holes collide during galaxy mergers, reorganizing stellar orbits into a lopsided, eccentric disk around the recoiling black hole. This is precisely what is observed in the nucleus of our nearest major galaxy neighbor, Andromeda, which suggests that Andromeda might harbor a recoiled black hole that has returned to the galaxy’s nucleus through dynamical friction. A 3-year research program led by investigators at the University of Colorado at Boulder will rigorously test this hypothesis. The team will compare computer simulations with observations of the Andromeda nucleus to determine merger event rates and characteristics of high-energy transients following a merger. The investigators will implement a series of Sensory-Friendly planetarium experiences at the University of Colorado Boulder. Guidelines and activities will be developed in collaboration with the Autism Society of Boulder County and the Speech, Language, and Hearing Clinic at the University of Colorado Boulder. These events, accessible to all, would broaden theater participation to neurodiverse children, opening the full dome experience and wonders of the night sky to all families. The investigators will use theoretically motivated initial conditions for stellar distributions, designing a fiducial model to explore the Andromeda major merger event 2-4 billion years ago: a million solar mass merger with recoil kick magnitude of 300 km/s. Simulations will track 10^6 particles that interact only with the central body. The simulation will be paused immediately following the recoil kick after calculating new orbits. In the region where apsidal alignment is strongest, the investigators will select 10^4 stars and switch them to being massive particles, allowing them to evolve the system forward in time (10 million years) until reaching equilibrium. These high-resolution N-body simulations will explore stellar dynamics, particularly the influence of lopsided stellar disks on the dynamical friction timescale for recoiling black holes to return to their galactic centers. Conclusively identifying the Andromeda nucleus as the nearest recoiled black hole system would allow its use as a laboratory to probe the physics of gravitational wave recoil kicks, supermassive black hole growth, galaxy evolution, and stellar dynamics. Furthermore, this research could provide a blueprint for identifying recoiled supermassive black holes in other local galaxies. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.