Resolving Galaxy Nuclei and Compact Stellar Systems as Engines of Galaxy Evolution

TL;DR

The white paper argues that compact stellar systems and galactic nuclei are central to galaxy evolution and black hole demographics, proposing a kilometre-scale optical/IR interferometer to resolve sub-parsec scales out to the Virgo/Forna clusters. This facility would enable precise dynamical black hole masses in NSCs, UCDs, and stripped nuclei, map chemo-dynamical properties, and link local low-massBH populations to high-redshift analogues. It also outlines substantial ancillary science in secular AGN fueling, stellar surfaces and binaries, and exoplanet atmospheres, leveraging a diffraction-limited integral-field spectrograph alongside long-baseline interferometry. A pragmatic ESO-centric architecture with 3–4 X-telescopes and a standalone X1 IFS module aims to maximize scientific return while reusing existing infrastructure and emphasizing sustainable, modular deployment and renewable-energy integration.

Abstract

In this white paper we focus on compact stellar systems, star clusters, nuclear star clusters (NSCs), stripped nuclei, and ultra-compact dwarfs (UCDs), as engines of galaxy evolution and black-hole growth. We show how the same capability also enables transformative science in active galactic nucleus (AGN) fuelling, stellar surfaces and interacting binaries, and exoplanet atmospheres. These science drivers are naturally aligned with a next-generation kilometre-scale optical/IR interferometer for the 2040s that reuses existing ESO infrastructure while adding diffraction-limited integral-field spectroscopy (IFS).