Nuclear Star Clusters across the Hubble Sequence

TL;DR

This paper reviews recent findings on nuclear star clusters in galaxies, highlighting their properties, formation theories, and potential links to supermassive black holes across different galaxy types.

Contribution

It provides a comprehensive overview of observational results and discusses current ideas and open questions about the formation and evolution of nuclear star clusters.

Findings

NCs are present in all galaxy types.

They have stellar origins confirmed by structural and spectral analysis.

Open issues include their connection to supermassive black holes.

Abstract

Over the last decade, HST imaging studies have revealed that the centers of most galaxies are occupied by compact, barely resolved sources. Based on their structural properties, position in the fundamental plane, and spectra, these sources clearly have a stellar origin. They are therefore called ``nuclear star clusters'' (NCs) or ``stellar nuclei''. NCs are found in galaxies of all Hubble types, suggesting that their formation is intricately linked to galaxy evolution. In this contribution, I briefly review the results from recent studies of NCs, touch on some ideas for their formation, and mention some open issues related to the possible connection between NCs and supermassive black holes.