An order-disorder phase transition in black-hole star clusters

Abstract

The centers of most galaxies contain massive black holes surrounded by dense star clusters. The structure of these clusters determines the rate and properties of observable transient events, such as flares from tidally disrupted stars and gravitational-wave signals from stars spiraling into the black hole. Most estimates of these rates enforce spherical symmetry on the cluster. Here we show that, in the course of generic evolutionary processes, a star cluster surrounding a black hole can undergo a robust phase transition from a spherical thermal equilibrium to a lopsided equilibrium, in which most stars are on high-eccentricity orbits with aligned orientations. The rate of transient events is expected to be much higher in the ordered phase. Better models of cluster formation and evolution are needed to determine whether clusters should be found in the ordered or disordered phase.

5 pages, 2 figures

References in corpus (1)

• Three-dimensional Keplerian orbit-superposition models of the nucleus of M31

Cited by in corpus (4)

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• Order-disorder phase transition in black-hole star clusters -- III. A mono-energetic cluster
• Order-disorder phase transition in black-hole star clusters. II. A scale-free cluster
• Apsidal Clustering following the Inclination Instability