On the Existence of Pulsars in the Vicinity of the Massive Black Hole in the Galactic Center

Zhang, Fupeng; Lu, Youjun; Yu, Qingjuan

doi:10.1088/0004-637x/784/2/106

Cited by 26 publications

(30 citation statements)

References 62 publications

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“…Previously, the absence of Galactic center pulsars was attributed to extreme temporal broadening at low radio frequencies and the steep spectra of radio pulsars. Theory, however, has predicted populations of hundreds to thousands of pulsars bound to Sgr A* based on the high rate of star formation and the large massive star population (e.g., Pfahl & Loeb 2004;Freitag et al 2006;Wharton et al 2012;Zhang et al 2014). The massive stars may have produced ∼20 pulsar wind nebulae in the central 20 pc, as seen through extended X-ray emission (Muno et al 2008).…”

Section: Introductionmentioning

confidence: 99%

The Proper Motion of the Galactic Center Pulsar Relative to Sagittarius A*

Bower¹,

Deller

Demorest

et al. 2015

ApJ

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We measure the proper motion of the pulsar PSR J1745-2900 relative to the Galactic center massive black hole, Sgr A*, using the Very Long Baseline Array (VLBA). The pulsar has a transverse velocity of 236 ± 11 km s −1 at position angle 22 ± 2 deg east of north at a projected separation of 0.097 pc from Sgr A*. Given the unknown radial velocity, this transverse velocity measurement does not conclusively prove that the pulsar is bound to Sgr A*; however, the probability of chance alignment is very small. We do show that the velocity and position are consistent with a bound orbit originating in the clockwise disk of massive stars orbiting Sgr A* and a natal velocity kick of 500 km s −1 . An origin among the isotropic stellar cluster is possible but less probable. If the pulsar remains radiobright, multiyear astrometry of PSR J1745-2900 can detect its acceleration and determine the full three-dimensional orbit. We also demonstrate that PSR J1745-2900 exhibits the same angular broadening as Sgr A* over a wavelength range of 3.6 cm to 0.7 cm, further confirming that the two sources share the same interstellar scattering properties. Finally, we place the first limits on the presence of a wavelength-dependent shift in the position of Sgr A*, i.e., the core shift, one of the expected properties of optically thick jet emission. Our results for PSR J1745-2900 support the hypothesis that Galactic center pulsars will originate from the stellar disk and deepen the mystery regarding the small number of detected Galactic center pulsars.

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Section: Introductionmentioning

confidence: 99%

The Proper Motion of the Galactic Center Pulsar Relative to Sagittarius A*

Bower¹,

Deller

Demorest

et al. 2015

ApJ

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“…Nor is it likely that they migrated to these distance through secular dynamical process (e.g., by two body relaxation processes) as the corresponding timescale is much longer than the lifetime of the pulsar and the progenitor stars. A plausible model is that their progenitors are captured by the MBH through tidal break up of binary stars (Zhang et al 2014). By including the supernova kick, secular dynamic relaxations and gravitational wave decay, Zhang et al (2014) estimated that a number of ∼ 10 − 15 pulsars are expected to be hidden within distance of 1000 AU from the black hole.…”

Section: The Orbits Of Hypothetical Pulsarsmentioning

confidence: 99%

Probing the Spinning of the Massive Black Hole in the Galactic Center via Pulsar Timing: A Full Relativistic Treatment

Zhang

Saha

2017

ApJ

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Pulsars around the Massive Black Hole (MBH) in the Galactic Center (GC) are expected to be revealed by the incoming facilities (e.g., the Square Kilometre Array). Under a full relativistic framework with the pulsar approximated as a test particle, we investigate the constraints on the spinning of the MBH by monitoring the timing of surrounding pulsars. For GC pulsars orbiting closely around the MBH (e.g., 1000AU), we find that full relativistic treatment in modeling accurately their timing signals can be necessary, as the relativistic signals are orders of magnitude larger than the time of arrival measurement accuracies. Although usually there are near-degeneracies among MBH spin parameters, the constraints on the spinning of the MBH are still very tight. By continuously monitoring a normal pulsar in orbits with a period of ∼ 2.6yr and an eccentricity of 0.3 − 0.9 under timing precision of 1 − 5ms, within ∼ 8yr the spin magnitude and the orientations of the GC MBH can be constrained with 2σ error of 10 −3 − 10 −2 and 10 −1 − 10 • , respectively. Even for pulsars in orbits similar to the detected star S2/S0-2 or S0-102, we find that the spinning of the MBH can still be constrained within 4 − 8yr, with the most significant constraints provided near the pericenter passage. If the proper motion of the pulsars with astrometric accuracy of 10µas can also be collected along with the timing measurement, then the position, velocity, mass and the distance to the Solar System of the MBH can be constrained about ∼ 10µas, ∼ 1µas/yr, ∼ 10M ⊙ and ∼ 1pc, respectively.

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“…Dynamical simulations suggest that pulsars possibly exist in the intermediate vicinity around the MBH in the GC (e.g., Zhang et al 2014). If they are close enough to the MBH, the high order GR effects, including the frame-dragging and quadrupole effects, can be probed by their precise timing signals.…”

Section: Discussionmentioning

confidence: 99%

On the Newtonian and Spin-Induced Perturbations Felt by the Stars Orbiting Around the Massive Black Hole in the Galactic Center

Zhang

Iorio

2017

ApJ

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The S-stars discovered in the Galactic center (GC) are expected to provide unique dynamical tests of the Kerr metric of the massive black hole (MBH) orbited by them. In order to obtain unbiased measurements of its spin and the related relativistic effects, a comprehensive understanding of the gravitational perturbations of the stars and stellar remnants around the MBH is quite essential. Here, we study the perturbations on the observables of a typical target star, i.e., the apparent orbital motion and the redshift, due to both the spin-induced relativistic effects and the Newtonian attractions of a single or a cluster of disturbing object(s). We find that, in most cases, the Newtonian perturbations on the observables are mainly attributed to the perturbed orbital period of the target star, rather than the Newtonian orbital precessions. The Newtonian perturbations have their unique features when they peak around the pericenter passage in each revolution, which is quite different from those of the spin-induced effects. Looking at the currently detected star S2/S0-2, we find that its spin-induced effects on both the image position and redshift are very likely obscured by the gravitational perturbations from the star S0-102 alone. We also investigate and discuss the Newtonian perturbations on a hypothetical S-star located inside the orbits of the currently detected ones. By considering a number of possible stellar distributions near the central MBH, we find that the spin-induced effects on the apparent position and the redshift dominate over the stellar perturbations for target stars with orbital semimajor axis smaller than 100 − 400 AU if the MBH is maximally spinning. Our results suggest that, in principle, the stellar perturbations can be removed as they have distinctive morphologies comparing to those of the relativistic Kerr-type signatures.

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On the Existence of Pulsars in the Vicinity of the Massive Black Hole in the Galactic Center

Cited by 26 publications

References 62 publications

The Proper Motion of the Galactic Center Pulsar Relative to Sagittarius A*

The Proper Motion of the Galactic Center Pulsar Relative to Sagittarius A*

Probing the Spinning of the Massive Black Hole in the Galactic Center via Pulsar Timing: A Full Relativistic Treatment

On the Newtonian and Spin-Induced Perturbations Felt by the Stars Orbiting Around the Massive Black Hole in the Galactic Center

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