ON POST-NEWTONIAN ORBITS AND THE GALACTIC-CENTER STARS

Journal Article · Thu Oct 01 00:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/703/2/1743· OSTI ID:21371876

Preto, Miguel ^[1]; Saha, Prasenjit ^[2]

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1. Astronomisches Rechen-Institut, Zentrum fuer Astronomie, University of Heidelberg, D-69120 Heidelberg (Germany)
2. Institute for Theoretical Physics, University of Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland)

Stars near the Galactic center reach a few percent of light speed during pericenter passage, which makes post-Newtonian effects potentially detectable. We formulate the orbit equations in Hamiltonian form such that the O(v {sup 2}/c {sup 2}) and O(v {sup 3}/c {sup 3}) post-Newtonian effects of the Kerr metric appear as a simple generalization of the Kepler problem. A related perturbative Hamiltonian applies to photon paths. We then derive a symplectic integrator with adaptive time steps, for fast and accurate numerical calculation of post-Newtonian effects. Using this integrator, we explore relativistic effects. Taking the star S2 as an example, we find that general relativity would contribute tenths of mas in astrometry and tens of km s{sup -1} in kinematics. (For eventual comparison with observations, redshift and time-delay contributions from the gravitational field on light paths will need to be calculated, but we do attempt these in the present paper.) The contribution from stars, gas, and dark matter in the Galactic center region is still poorly constrained observationally, but current models suggest that the resulting Newtonian perturbation on the orbits could plausibly be of the same order as the relativistic effects for stars with semimajor axes approx>0.01 pc (or 250 mas). Nevertheless, the known and distinctive time dependence of the relativistic perturbations may make it possible to disentangle and extract both effects from observations.

• OSTI ID: 21371876
• Journal Information: Astrophysical Journal, Vol. 703, Issue 2; Other Information: DOI: 10.1088/0004-637X/703/2/1743; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
GALAXIES
GENERAL RELATIVITY THEORY
GRAVITATIONAL FIELDS
HAMILTONIANS
KERR METRIC
NONLUMINOUS MATTER
ORBITS
PERTURBATION THEORY
PHOTONS
RED SHIFT
RELATIVISTIC RANGE
STARS
TIME DELAY
TIME DEPENDENCE
BOSONS
ELEMENTARY PARTICLES
ENERGY RANGE
FIELD THEORIES
MASSLESS PARTICLES
MATHEMATICAL OPERATORS
MATTER
METRICS
QUANTUM OPERATORS
RELATIVITY THEORY