Internal gas models and central black hole in 47 Tucanae using millisecond pulsars

TL;DR

This study uses millisecond pulsar timing data to measure ionized gas content and constrain the presence of a central black hole in 47 Tucanae, refining previous estimates and testing various models.

Contribution

It provides updated measurements of ionized gas density and assesses the necessity of an intermediate mass black hole in 47 Tucanae using extensive pulsar timing data.

Findings

Confirmed ionized gas with density $n= 0.23 ext{cm}^{-3}$, larger than previous estimates.

Disfavored models with decreasing or stellar-density-following gas distribution.

Black hole mass upper limit of approximately 4000 solar masses.

Abstract

Despite considerations of mass loss from stellar evolution suggesting otherwise, the content of gas in globular clusters seems poor and hence its measurement very elusive. One way of constraining the presence of ionized gas in a globular cluster is through its dispersive effects on the radiation of the millisecond pulsars included in the cluster. This effect led Freire et al. in 2001 to the first detection of any kind of gas in a globular cluster in the case of 47 Tucanae. By exploiting the results of 12 additional years of timing, as well as the observation of new millisecond pulsars in 47 Tucanae, we revisited this measurement: we first used the entire set of available timing parameters in order to measure the dynamical properties of the cluster and the three-dimensional position of the pulsars. Then we applied and tested various gas distribution models: assuming a constant gas density, we confirmed the detection of ionized gas with a number density of $n= 0.23\pm 0.05$ cm$^{-3}$, larger than the previous determination (at 2$\sigma$ uncertainty). Models predicting a decreasing density or following the stellar distribution density are highly disfavoured. We are also able to investigate the presence of an intermediate mass black hole in the centre of the cluster, showing that is not required by the available data, with an upper limit for the mass at $\sim 4000$ M$_{\odot}$.