Clearing the Gas from Globular Clusters & Dwarf Spheroidals with Classical Novae

TL;DR

This paper investigates how classical novae explosions can effectively clear intra-cluster gas from globular clusters, explaining observed gas deficiencies and predicting the impact on clusters of different masses.

Contribution

It models nova ejecta dynamics and demonstrates that classical novae can remove intra-cluster medium in low-mass globular clusters, providing a mechanism for observed gas deficiencies.

Findings

Nova shells escape before cooling in low-mass clusters.

Higher-mass clusters may retain gas due to longer quiescent periods.

The mechanism applies to ultra-faint Milky Way satellites.

Abstract

Observations of the intra-cluster medium (ICM) in galactic globular clusters (GCs) show a systematic deficiency in ICM mass as compared to that expected from accumulation of stellar winds in the time available between galactic plane crossings. In this paper, we reexamine the original hypothesis of Scott and Durisen that hydrogen-rich explosions on accreting white dwarfs, classical novae (CNe), will sweep out the ICM from the cluster more frequently than galactic plane crossings. From the CNe rate and stellar mass-loss rate, this clearing mechanism predicts that ~ 0.03 M_sun should be present in <= 10^5 M_sun GCs. We model the expanding remnant made from the 10^-4 M_sun nova ejecta and show that it escapes long before it has cooled. We discuss the few positive ICM measurements and use a Monte-Carlo simulation of the accumulation and CNe recurrence times to reveal the possible variance in the ICM masses for the higher mass (> 5x10^5 M_sun) GCs. We find that nova shells are effective at clearing the ICM in low-mass GCs (<= 10^5 M_sun), whereas higher-mass clusters may experience a quiescent time between novae long enough to prevent the next nova shell from escaping. The nova clearing mechanism will also operate in ultra-faint Milky Way satellites, where many upper limits on gas masses are available.