Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Time-domain astronomy

TL;DR

The paper argues for a Northern Hemisphere 30–40 m optical/IR telescope (a Northern ELT) to enable rapid, deep follow-up of fast, faint transients in the 2040s. It specifies capabilities—rapid response, broad $0.3$–$14$ μm coverage, high-time-resolution spectroscopy, polarimetry, AO, and automated, multi-messenger–driven operations—to capture the earliest diagnostic phases. Science cases span GRBs, various supernovae, FXTs, LFBOTs, TDEs, FRBs, and cross-scale accretion physics, emphasizing early-phase spectroscopy and environment studies. The proposal highlights La Palma's unique suitability and longitudinal complementarity to southern facilities, arguing for near-continuous global transient access when combined with ESO's ELT.

Abstract

We outline the science case for a 30-40 m optical/infrared telescope in the Northern Hemisphere, optimised for transformative time-domain astronomy in the 2040s. Upcoming multi-wavelength and multi-messenger facilities will reveal fast, faint, rapidly evolving Northern transients whose earliest phases carry decisive diagnostics. A Northern ELT with rapid response, broad wavelength coverage, high time resolution, polarimetric capabilities, and diffraction-limited imaging is essential to capture these phases and secure deep spectroscopy and photometry as transients fade. These capabilities will enable recovery of key physical information and detailed characterisation of transient environments, while also enabling unprecedented studies of accretion phenomena at all scales. Among potential sites, La Palma uniquely combines atmospheric stability, complementary longitude to ESO's ELT, protected dark skies, and robust infrastructure to host this facility.