Colloquium
Blue stragglers and friends: Stellar interactions in star clusters

Abstract

Interacting binary evolutionary products are ubiquitous in cluster environments. This talk presents an overview of recent observational progress on blue stragglers and related post-interaction systems, including blue lurkers, yellow stragglers, and extremely low-mass white dwarfs. These objects trace alternative evolutionary pathways and occupy regions of the Hertzsprung–Russell diagram that are inaccessible to single stars, reflecting a diversity of mass-transfer histories and evolutionary states in cluster environments. Multiwavelength observations, particularly in the ultraviolet, have proven to be powerful tools for identifying compact companions and constraining the present-day binarity and origins of these systems. In combination, time-series photometry and spectroscopic follow-up provide the most direct means of measuring their fundamental parameters and extending insights from cluster populations to analogous systems in the field.