Mapping the galactic gravitational potential with peculiar acceleration

TL;DR

This paper explores how measuring peculiar acceleration in our Galaxy can help map its gravitational potential and test gravity theories, using models like Kuzmin disc and MOND, with some detectable signals in globular clusters.

Contribution

It provides the first detailed estimate of Galactic peculiar acceleration signals for globular clusters and compares predictions from dark matter and MOND models.

Findings

Some globular clusters show velocity shifts >20 cm/sec over 15 years.

The acceleration pattern differs between dark matter and MOND models.

Detecting these signals could help test gravity theories, but may be challenging.

Abstract

It has been suggested recently that the change in cosmological redshift (the Sandage test of expansion) could be observed in the next generation of large telescopes and ultra-stable spectrographs. In a recent paper we estimated the change of peculiar velocity, i.e. the peculiar acceleration, in nearby galaxies and clusters and shown it to be of the same order of magnitude as the typical cosmological signal. Mapping the acceleration field allows for a reconstruction of the galactic gravitational potential without assuming virialization. In this paper we focus on the peculiar acceleration in our own Galaxy, modeled as a Kuzmin disc and a dark matter spherical halo. We estimate the peculiar acceleration for all known Galactic globular clusters and find some cases with an expected velocity shift in excess of 20 cm/sec for observations fifteen years apart, well above the typical cosmological acceleration. We then compare the predicted signal for a MOND (modified Newtonian dynamics) model in which the spherical dark matter halo is absent. We find that the signal pattern is qualitatively different, showing that the peculiar acceleration field could be employed to test competing theories of gravity. However the difference seems too small to be detectable in the near future.