Abstract

Contributed Talk - Plenary

Spaceborne VLBI: BHEX and Future Mission Concepts

Ben Hudson
TU Delft

Very long Baseline Interferometry (VLBI) provides the finest angular resolution of all astronomical observation techniques. The Event Horizon Telescope (EHT) has demonstrated this in recent years with the landmark achievement of resolving the shadows of the supermassive black holes M87* and Sgr A*. However, the only way to overcome fundamental limits on angular resolution of Earth-based arrays is to place part of or the entire interferometer in space. Two dedicated space-based VLBI missions have flown as of the time of writing: VSOP-HALCA and RadioAstron. Other mission concepts have been proposed in recent years, including the Black Hole Explorer (BHEX). BHEX will perform the first detection of a black hole’s photon ring by achieving an angular resolution of 6 µas. BHEX will also study AGN jets and black hole demographics through resolving an additional 5-10 black hole shadows. The concept will be submitted as a proposal to NASA’s Small Explorers (SMEX) programme in 2025. BHEX will perform ground-space VLBI, extending the EHT, with a collaboration of ground-based radio telescopes. The full advantage of spaceborne VLBI can be realised by placing the entire interferometer system in space, such as proposed for the TeraHertz Exploration and Zooming-in for Astrophysics (THEZA) concept. Building upon THEZA, here we also present a concept for a spaceborne interferometer with the aim of directly imaging Supermassive Black Hole Binaries (SMBHBs) for the first time. Such a system would make a powerful addition to multi-messenger astronomy, with strong synergies with gravitational wave observatories such as LIGO, LISA and PTAs.