Periastron shifts of stellar orbits near the Galactic Center

AbstractOne of the Milky Way's fundamental parameters is the distance of the Sun from the Galactic Center, R0. This article reviews the various ways of estimating R0, placing special emphasis on methods that have become possible recently. In particular, we focus on the geometric distance estimate made possible thanks to observations of individual stellar orbits around the massive black hole at the center of the Galaxy. The specific issues of concern there are the degeneracies with other parameters, most importantly the mass of the black hole and the definition of the reference frame. The current uncertainty is nevertheless only a few percent, with error bars shrinking every year.

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An Adaptive Scheduling Tool to Optimize Measurements to Reach a Scientific Objective: Methodology and Application to Measurements of Stellar Orbits in the Galactic Center

The Astrophysical Journal ◽

10.3847/1538-4357/ab2ae0 ◽

2019 ◽

Vol 880 (2) ◽

pp. 87

Author(s):

A. Hees ◽

A. Dehghanfar ◽

T. Do ◽

A. M. Ghez ◽

G. D. Martinez ◽

...

Keyword(s):

Galactic Center ◽

Adaptive Scheduling ◽

Scientific Objective ◽

Stellar Orbits ◽

Scheduling Tool ◽

Objective Methodology

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Stellar Orbits in the Galactic Center, QED

Revealing the Heart of the Galaxy ◽

10.1017/cbo9781139856546.010 ◽

2013 ◽

pp. 129-148

Author(s):

Robert H. Sanders

Keyword(s):

Galactic Center ◽

Stellar Orbits

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15 years of high precision astrometry in the Galactic Center

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308019820 ◽

2007 ◽

Vol 3 (S248) ◽

pp. 466-469

Author(s):

S. Gillessen ◽

R. Genzel ◽

F. Eisenhauer ◽

T. Ott ◽

S. Trippe ◽

...

Keyword(s):

Black Hole ◽

Mass Distribution ◽

Near Infrared ◽

Galactic Center ◽

Massive Black Hole ◽

Data Set ◽

Stellar Orbits ◽

Supermassive Black Hole ◽

Near Future ◽

Precision Astrometry

AbstractIn 1992, we obtained the first observations of S2 a star close to the supermassive black hole at the Galactic Center. In 2002, S2 passed its periastron and in 2007, it completed a first fully observed revolution. This orbit allowed us to determine the mass of and the distance to the supermassive black hole with unprecedented accuracy. Here we present a re-analysis of the data set, enhancing the astrometric accuracy to 0.5 mas and increasing the number of well-determined stellar orbits to roughly 15. This allows to constrain the extended mass distribution around the massive black hole and will lead in the near future to the detection of post-Newtonian effects. We will also give an outlook on the potential of interferometric near-infrared astrometry with 10 microarcsecond accuracy from the VLTI.

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Stellar Orbits in Doubly-Barred Galaxies

International Astronomical Union Colloquium ◽

10.1017/s0252921100050223 ◽

1996 ◽

Vol 157 ◽

pp. 464-466

Author(s):

H. Hasan

Keyword(s):

Galactic Center ◽

Observational Evidence ◽

Stellar Kinematics ◽

Stellar Orbits ◽

Barred Galaxies ◽

Secular Evolution

The question of bars within bars has been reviewed by Friedli and Martinet (1993), who have also performed N-body simulations to produce nested bars. They propose that if a system of embedded bars is effective in transporting gas to the galactic center (Shlosman et al. 1989), then it is perhaps a step in the secular evolution of barred galaxies. In order to pursue this interesting proposition, and also because observational evidence for the existence of secondary bars is mounting (e.g. Buta & Crocker 1993; Shaw et al. 1993, Wozniak et al. 1995), it is important to understand the stellar kinematics in such systems.

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Nonlocal gravity cosmology: An overview

International Journal of Modern Physics D ◽

10.1142/s0218271822300099 ◽

2021 ◽

Author(s):

Salvatore Capozziello ◽

Francesco Bajardi

Keyword(s):

Functional Form ◽

Galactic Center ◽

Equations Of Motion ◽

Analytic Solutions ◽

Accelerated Expansion ◽

Spherically Symmetric ◽

Nonlocal Effects ◽

Stellar Orbits ◽

Theories Of Gravity ◽

Nonlocal Terms

We discuss some main aspects of theories of gravity containing nonlocal terms in view of cosmological applications. In particular, we consider various extensions of general relativity based on geometrical invariants as [Formula: see text], [Formula: see text] and [Formula: see text] gravity where [Formula: see text] is the Ricci curvature scalar, [Formula: see text] is the Gauss–Bonnet topological invariant, [Formula: see text] the torsion scalar and the operator [Formula: see text] gives rise to nonlocality. After selecting their functional form by using Noether symmetries, we find out exact solutions in a cosmological background. It is possible to reduce the dynamics of selected models and to find analytic solutions for the equations of motion. As a general feature of the approach, it is possible to address the accelerated expansion of the Hubble flow at various epochs, in particular the dark energy issues, by taking into account nonlocality corrections to the gravitational Lagrangian. On the other hand, it is possible to search for gravitational nonlocal effects also at astrophysical scales. In this perspective, we search for symmetries of [Formula: see text] gravity also in a spherically symmetric background and constrain the free parameters, Specifically, by taking into account the S2 star orbiting around the Galactic Center SgrA[Formula: see text], it is possible to study how nonlocality affects stellar orbits around such a massive self-gravitating object.

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Statistical Challenges in fitting stellar orbits around the super-massive black hole at the Galactic center

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316012175 ◽

2016 ◽

Vol 11 (S322) ◽

pp. 239-240

Author(s):

Gregory D. Martinez ◽

Kelly Kosmo ◽

Aurelien Hees ◽

Joseph Ahn ◽

Andrea Ghez

Keyword(s):

General Relativity ◽

Black Hole ◽

Galactic Center ◽

Massive Black Hole ◽

Parameter Spaces ◽

Stellar Orbits ◽

Tests Of General Relativity ◽

Short Period ◽

Statistical Issues ◽

Radial Velocity Data

AbstractOver two decades of astrometric and radial velocity data of short period stars at the Galactic center has the potential to provide unprecedented tests of General Relativity and insight into the astrophysics of the super-massive black hole. Fundamental to this is understanding the underlying statistical issues of fitting stellar orbits. Unintended prior effects can obscure actual physical effects from General Relativity and underlying extended mass distribution. At the heart of this is dealing with large parameter spaces inherent to multi-star fitting and ensuring acceptable coverage properties of the resulting confidence intervals in the Bayesian framework. This proceeding will detail some of the UCLA group's analysis and work in addressing these statistical issues.

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