MG13 - Talk detail

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Abstract

Through the monitoring of stars and pulsars (as yet undiscovered) on orbits around Sgr A*, the metric in the vicinity of the black hole can be measured by way of stellar redshifts or pulsar timing. These orbits are ballistic trajectories which probe gravitational physics in the strongest field yet observed. We treat each orbit as a clock falling in the Kerr geometry, which emits ticks in equal intervals of proper time. These tick signals propagate on the same space-time until they reach the observer. We investigate Schwarzschild effects, as well as high-order Kerr signals, which include spin and spin-squared effects. We address remarks made in the literature linking such experiments to tests of the no-hair conjecture. If general relativity is correct, then geodesic tests of relativity in the Solar system and in binary pulsar systems probe the same metric as galactic center tests do. However, because the fields are orders of magnitude stronger, the relativistic effects expected from Sgr A* orbits are not simply scaled-up versions of the classic tests. Transient phenomena on the orbit, spin-squared effects, higher-order signal propagation delay or gravitational time dilation are among those neither observable in solar system nor on binary pulsar systems.

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