Abstract
The supermassive black hole at the Galactic center harbors a bound cluster of massive stars that should leave neutron star remnants. Extrapolating from the available data, we estimate that ~1000 radio pulsars may currently orbit Sgr A* with periods of ≲100 yr. Optimistically, 1-10 of the most luminous of these pulsars may be detectable with current telescopes in periodicity searches at frequencies near 10 GHz, where the effects of interstellar scattering are alleviated. Long-term timing observations of such a pulsar would clearly reveal its Keplerian motion and possibly show the effects of relativistic gravity. We briefly discuss how pulsar timing can be used to study the dynamical and interstellar environment of the central black hole and speculate on the prospects for astrometric observations of an orbiting pulsar.
Highlights
Ten years of near-infrared observations of the Galactic center have revealed the proper motions of nearly two dozen stars within 0.′′5 of the compact radio source Sgr A∗
If the central mass is confined within 100 AU, the implied density is 1016 M⊙ pc−3, which essentially rules out existing models alternative to the hypothesis that the central object is a supermassive black hole (BH; Maoz 1998; Ghez et al 2003b; Schödel et al 2003)
Evidence from the near-infrared spectrum of S0-2 (Ghez et al 2003a) and the integrated spectrum within ≃0.′′5 of Sgr A∗ (Genzel et al 1997; Eckart, Ott, & Genzel 1999; Figer et al 2000; Gezari et al 2002) suggest that the observed Sgr A∗ stellar cluster is largely comprised of luminous (∼104 L⊙), early-type (O9 to B0) stars
Summary
Ten years of near-infrared observations of the Galactic center have revealed the proper motions of nearly two dozen stars within 0.′′5 of the compact radio source Sgr A∗. Evidence from the near-infrared spectrum of S0-2 (Ghez et al 2003a) and the integrated spectrum within ≃0.′′5 of Sgr A∗ (Genzel et al 1997; Eckart, Ott, & Genzel 1999; Figer et al 2000; Gezari et al 2002) suggest that the observed Sgr A∗ stellar cluster is largely comprised of luminous (∼104 L⊙), early-type (O9 to B0) stars If these stars are near the main sequence, their masses are 10–20 M⊙. The observational census is incomplete, this volume likely contains at least several dozen massive stars It is not the present population of massive stars, but rather their predecessors, that are the progenitors of radio pulsars orbiting Sgr A∗. If there are ∼1000 radio pulsars with Porb uniformly distributed over, e.g., 1–100 yr, ∼100 pulsars may have Porb 10 yr
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