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Journal Article

Blocking low-eccentricity EMRIs: A statistical direct-summation N-body study of the Schwarzschild barrier


Amaro-Seoane,  Pau
Astrophysical and Cosmological Relativity, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;

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Brem, P., Amaro-Seoane, P., & Sopuerta, C. F. (2014). Blocking low-eccentricity EMRIs: A statistical direct-summation N-body study of the Schwarzschild barrier. Monthly Notices of the Royal Astronomical Society, 437(2), 1259-1267. doi:10.1093/mnras/stt1948.

Cite as: https://hdl.handle.net/11858/00-001M-0000-002A-803D-B
The capture of a compact object in a galactic nucleus by a massive black hole (MBH), an extreme-mass ratio inspiral (EMRI), is the best way to map space and time around it. Recent work on stellar dynamics has demonstrated that there seems to be a complot in phase space acting on low-eccentricity captures, since their rates decrease significantly by the presence of a blockade in the rate at which orbital angular momenta change takes place. This so-called "Schwarzschild barrier" is a result of the impact of relativistic precession on to the stellar potential torques, and thus it affects the enhancement on lower-eccentricity EMRIs that one would expect from resonant relaxation. We confirm and quantify the existence of this barrier using a statistical sample of 2,500 direct-summation N-body simulations using both a post-Newtonian and also for the first time in a direct-summation code a geodesic approximation for the relativistic orbits. The existence of the barrier prevents low-eccentricity EMRIs from approaching the central MBH, but high-eccentricity EMRIs, which have been wrongly classified as "direct plunges" until recently, ignore the presence of the barrier, because they are driven by two-body relaxation. Hence, since the rates are significantly affected in the case of low-eccentricity EMRIs, we predict that a LISA-like observatory such as eLISA will predominantly detect high-eccentricity EMRIs.