Nuclear Star Clusters and Bulges

TL;DR

Nuclear star clusters are dense stellar systems at galaxy centers, exhibiting properties and formation processes that relate to galaxy evolution and supermassive black holes, involving both dissipational and dissipationless mechanisms.

Contribution

This paper reviews the properties, scaling relations, and formation processes of nuclear star clusters, highlighting their connection to galaxy evolution and black hole growth.

Findings

Nuclear star clusters are common in various galaxy types.

They show scaling relations with their host galaxies.

Their formation involves both dissipational and dissipationless processes.

Abstract

Nuclear star clusters are among the densest stellar systems known and are common in both early- and late-type galaxies. They exhibit scaling relations with their host galaxy which may be related to those of supermassive black holes. These may therefore help us to unravel the complex physical processes occurring at the centres of galaxies. The properties of nuclear stellar systems suggest that their formation requires both dissipational and dissipationless processes. They have stellar populations of different ages, from stars as old as their host galaxy to young stars formed in the last 100 Myr. Therefore star formation must be happening either directly in the nuclear star cluster or in its vicinity. The secular processes that fuel the formation of pseudobulges very likely also contributes to nuclear star cluster growth.