Orateur
Description
Unlocking the Dynamic Universe: The Case for WST as a Spectroscopic Time-Domain Machine
The dynamic universe is one of the defining scientific frontiers of the coming decades, yet our ability to fully explore it is fundamentally constrained by a spectroscopic bottleneck that will only deepen in the 2040s. Photometric surveys such as LSST and Gaia, and multi-messenger observatories including gravitational-wave detectors, will deliver unprecedented volumes of transient discoveries, but they can only tell part of the story. Photometric classification remains ambiguous, gravitational-wave localizations are coarse, and neither can unlock the physical information encoded in spectra. Answering the key scientific questions of the 2040s — spanning Solar System bodies and minor planets, stellar formation and evolution, variable and transient events, black hole demographics from stellar-mass to supermassive, AGN activity across cosmic time, and the electromagnetic characterization of gravitational-wave sources — demands a massively multiplexed wide-field spectroscopic facility designed with time-domain operations at its heart. The Wide-Field Spectroscopic Telescope (WST), with its combination of a large collecting area, wide field of view, and massive multiplex capability across both MOS and IFU modes, is uniquely positioned to serve as this facility. A critical component of the WST design is a spectroscopic alert system: one capable of ingesting photometric and multi-messenger alert streams, autonomously classifying and prioritizing targets, triggering alerts when spectroscopic variations are detected across the multi-epoch survey, and delivering science-ready spectra in near real time. Far from being simply a more efficient follow-up machine, WST equipped with such capabilities opens an entirely new observational window. The ability to obtain spectra of large numbers of variable and transient events immediately and without prior photometric selection breaks the classification bias inherent to all current approaches, creating the conditions for discovering entirely new classes of phenomena. Serendipity, in this regime, becomes systematic. In this talk, I will present the time-domain science cases that define the requirements for WST's spectroscopic alert capabilities, and argue that embedding these capabilities into the WST design from the outset is essential to realize its full potential as a transformational facility for ground-based astronomy in the 2040s.