Project information
DISCO - Distances from Star Cluster Observations (dr.Katja Fahrion)

Distances are fundamental to astrophysics and observational cosmology: they are required to measure galaxy properties and to constrain the expansion rate of the Universe. Current methods, such as Cepheid variables, the tip of the red giant branch (TRGB), and surface brightness fluctuations (SBF), are however sensitive to environment or galaxy type. These limitations have become particularly critical in the context of the ongoing “Hubble tension”, the discrepancy between early- and late-Universe measurements of the Hubble constant.
The DISCO (Distances from Star Cluster Observations) project introduces a novel, physically motivated distance indicator using the tight relation between the luminosities of globular clusters (GCs) and their internal stellar velocity dispersions (the GC velocity dispersion method GCVD). By comparing observed magnitudes and velocity dispersions to a calibrated relation, distances can be inferred with high precision, as our pilot studies demonstrate. DISCO will a) quantify how stellar population variations and dynamical effects influence the GCVD relation, b) test whether related systems such as nuclear star clusters and ultra-compact dwarfs can be incorporated, and c) apply the GCVD method to a well-characterised sample of galaxies to validate its performance and obtain a first GCVD-based measurement of the Hubble constant.
DISCO builds on a novel dataset of high-resolution spectroscopy that I have secured through successful observing proposals, comprising more than 1200 globular clusters. Combined with photometric catalogues, this dataset provides the foundation to calibrate and apply the GCVD method systematically for the first time. In this way, DISCO will establish the GCVD method as a competitive alternative to classical distance indicators and as a new rung on the extragalactic distance ladder, ready for exploitation with upcoming facilities.