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Title: Constraining the dark cusp in the galactic center by long-period binaries

Massive black holes (MBHs) in galactic nuclei are believed to be surrounded by a high-density stellar cluster, whose mass is mostly in hard-to-detect faint stars and compact remnants. Such dark cusps dominate the dynamics near the MBH: a dark cusp in the Galactic center (GC) of the Milky Way would strongly affect orbital tests of general relativity there; on cosmic scales, dark cusps set the rates of gravitational wave emission events from compact remnants that spiral into MBHs, and they modify the rates of tidal disruption events, to list only some implications. A recently discovered long-period massive young binary (with period P {sub 12} ≲ 1 yr, total mass M{sub 12}∼O(100 M{sub ⊙}), and age T {sub 12} ∼ 6 × 10{sup 6} yr), only ∼0.1 pc from the Galactic MBH, sets a lower bound on the stellar two-body relaxation timescale there, min t {sub rlx}∝(P {sub 12}/M {sub 12}){sup 2/3} T {sub 12} ∼ 10{sup 7} yr, and, correspondingly, an upper bound on the stellar number density, maxn{sub ⋆}∼few×10{sup 8}/〈M{sub ⋆}{sup 2}〉 pc{sup −3} (〈M{sub ⋆}{sup 2}〉{sup 1/2} is the rms stellar mass), based on the binary's survival against evaporation by the dark cusp. However, a conservative dynamical estimate,more » the drain limit, implies t{sub rlx}>O(10{sup 8} yr). Such massive binaries are thus too short-lived and tightly bound to constrain a dense relaxed dark cusp. We explore here in detail the use of longer-period, less massive, and longer-lived binaries (P {sub 12} ∼ few yr, M {sub 12} ∼ 2-4 M {sub ☉}, T {sub 12} ∼ 10{sup 8}-10{sup 10} yr), presently just below the detection threshold, for probing the dark cusp and develop the framework for translating their future detections among the giants in the GC into dynamical constraints.« less
Authors:
 [1] ;  [2]
  1. Department of Particle Physics and Astrophysics, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100 (Israel)
  2. Max-Planck-Institut für extraterrestriche Physik, Postfach 1312, D-85741 Garching (Germany)
Publication Date:
OSTI Identifier:
22348245
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 780; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; DENSITY; DETECTION; EMISSION; EVAPORATION; GALAXY NUCLEI; GENERAL RELATIVITY THEORY; GRAVITATIONAL WAVES; LIMITING VALUES; MASS; MILKY WAY; STARS