Towards an extended VLTI: a roadmap for kilometer baseline interferometry at Paranal Observatory

Abstract

In the 2030s, optical/IR interferometry will be the natural next step to push angular resolution beyond the current VLT/I and ELTs. Key astrophysical questions in that time-frame are the fundamental tests of General Relativity, the evolution of supermassive black holes across cosmic time, the understanding of exoplanet atmosphere, internal physics and exomoons, and planet formation down to terrestrial orbits. For these questions, we need to resolve astrophysical scales at sub-milliarcsecond scales down to micro-arcsecond scales. In this talk, we propose the extension of the VLT/I facility to additional telescopes and longer, up to kilometer baseline interferometry (KBI). We focus on the case study of a VLTI-VISTA baseline, offering a 1.4km baseline with 4m to 8m class telescope in the infrared. We present the development of new solutions for beam-transportation, combination of telescopes with different diameter and design, multi-delay tracking, and lightweight telescope design. An additional high-angular resolution telescope could also be used as a platform for high-contrast technique in standalone operations. With its large collecting area compatible with the surface brightness sensitivity required for kilometer baseline, VLTI is a unique platform world-wide to carry extension of infrared interferometry arrays and pathfinder demonstrations.