Gaps in stellar streams as a result of globular cluster flybys

The case of Palomar 5

¹ LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 92190 Meudon, France
² Department of Physics, University of Rome “La Sapienza”, Piazzale Aldo Moro 5, 00185 Rome, Italy
³ Institute for Complex Systems CNR, Piazzale Aldo Moro 2, 00185 Rome, Italy
⁴ Dipartimento di Fisica e Astronomia. “Galileo Gallilei” Università di Padova, Vicolo dell’Osservatorio 3 Padova 35122, Italy
⁵ Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
⁶ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁷ UNIDIA, Observatoire de Paris, Université PSL, CNRS, 92190 Meudon, France
⁸ DTIS, ONERA, Université Paris Saclay, 91123 Palaiseau, France
⁹ LUX, CNRS UMR 8252, Observatoire de Paris, PSL, 61 Avenue de l’Observatoire, 75014 Paris, France
¹⁰ Department of Physics and Astronomy, University of Exeter, Stocker Rd, Exeter EX4 4QL, UK

^★ Corresponding author: salvatore.ferrone@obspm.fr

Received: 27 January 2025
Accepted: 26 May 2025

Abstract

Context. Thin stellar streams, such as those resulting from the tidal disruption of globular clusters, have long been known and used as probes of the gravitational potential of our Galaxy, both its visible and dark contents. The literature commonly interprets the presence of underdensity regions, or gaps, along these streams as being due to the close passage of dark matter subhalos.

Aims. In this work, we investigate the perturbations induced on streams by the passage of dense stellar systems, such as globular clusters themselves, to test the possibility that they may cause the formation of gaps as well. In particular, we focus on the study of the stream generated by a cluster with characteristics (mass, size, and orbit) similar to those of Palomar 5, a well-known globular cluster in the Galactic halo that has particularly long tidal tails.

Methods. For this purpose, we used a particle-test code to simulate the formation and evolution of the stream when subjected to the Galaxy’s gravitational field plus its whole system of globular clusters.

Results. Our study shows that such a stream can be strongly perturbed by the close passage of other clusters, in particular NGC 2808, NGC 7078, and NGC 104, and that these perturbations induce the formation of gaps in the tails.

Conclusions. The results of this work show that globular clusters can induce gaps in cold streams–just as it has been demonstrated in the literature for that other baryonic components, such as giant molecular clouds and the Galactic bar. Therefore, a future work that attempts to infer the dark matter subhalo distribution from stellar stream gaps must include the contributions from globular clusters.