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Astrometric and spectroscopic monitoring of individual stars orbiting the supermassive black hole in the Galactic Center offer a promising way to detect general relativistic effects. While low-order effects are expected to be detected following the periastron passage of S2 in Spring 2018, detecting higher order effects due to black hole spin will require the discovery of closer stars. In this paper, we set out to determine the requirements such a star would have to satisfy to allow the detection of black hole spin. We focus on the instrument GRAVITY, which saw first light in 2016 and which is expected to achieve astrometric accuracies |$10\hbox{--}100 \, \mu$| as. For an observing campaign with duration T years, total observations N obs, astrometric precision σ x , and normalized black hole spin χ, we find that |$a_{\rm orb}(1-e^2)^{3/4} \lesssim 300 R_{\rm S} \sqrt{\frac{T}{4\, {\rm {yr}}}} \left(\frac{N_{\rm obs}}{120}\right)^{0.25} \sqrt{\frac{10\, \mu {\rm as}}{\sigma _x}} \sqrt{\frac{\chi }{0.9}}$| is needed. For χ = 0.9 and a potential observing campaign with |$\sigma _x = 10 \, \mu$| as, 30 observations yr−1 and duration 4–10 yr, we expect ∼0.1 star with K  < 19 satisfying this constraint based on the current knowledge about the stellar population in the central 1 arcsec. We also propose a method through which GRAVITY could potentially measure radial velocities with precision ∼50 km s−1. If the astrometric precision can be maintained, adding radial velocity information increases the expected number of stars by roughly a factor of 2. While we focus on GRAVITY, the results can also be scaled to parameters relevant for future extremely large telescopes. [ABSTRACT FROM AUTHOR]

Recently, more than 100 Wolf-Rayet and OB stars were identified in the Galactic center. About a third of these sources are not spatially associated with any of the known star clusters in this region. We probe the distribution of drifted sources in numerical models of the massive clusters in the Galactic center and compare it to the observed distribution of isolated massive sources in this region. We find that stars as massive as 100 M? drift away from the center of each cluster by up to ~ 60 pc using the cluster models. Our best model reproduces ~ 60% of the known isolated massive stars out to 80 pc from the center of the Arches cluster. This number increases to 70-80% when we only consider the region that is ~ 20 pc from the Arches cluster. [ABSTRACT FROM AUTHOR]