EHT goals and ambitions in the WSU era

Since 2019, when the first image of the supermassive black hole in M87 was released, the Event Horizon Telescope (EHT) augmented by ALMA has produced a series of groundbreaking results aimed at understanding the physics, dynamics and properties of these massive compact objects. The two main targets of the EHT collaboration are M87 and SgrA*, which, though comparable in angular sizes, display very different dynamics and properties like linear and circular polarisation. More recently, and thanks to the continued expansion of the EHT array (8 telescopes were available in 2017 in bands 3 and 6, while next year, in Cycle 11, there will be 11 telescopes available in bands 3, 6 and 7 and spectral line mode) more supermassive black holes have been observed and studied, as well as pulsar observations which were made possible by the phased array. Despite these early results, many fundamental questions still remain, e.g., on the exact nature of accretion and jet launching mechanisms. For this reason, new observations will greatly benefit from an improved the uv-coverage and more sensitive antennas, but also by exploring the time domain more extensively. To this end, making the first ever “movie” of the supermassive black hole in SgrA* on daily/weekly or monthly timescales will be a cruciall goal of the EHT in the coming years. Lastly, adding EHT space-based antennas will allow an even better uv-coverage and will likely play a crucial role in coming decades too. The WSU will positively impact EHT observations in several ways, and most critically, by providing a boost in sensitivity of x1.5 thanks to its digital and receiver improvements, which will improve the phasing efficiency and thus will allow to observe fainter calibrators. Also, phasing on multiple lines and allowing to use one ALMA antenna as stand-alone will help obtain faster and dynamic observations. ALMA sub-arraying could be an interesting application for the EHT as it would allow for simultaneous dual-band observations and thus phase transfer at the other sites - however fast switching between bands may work well enough to this purpose. Overall, because VLBI is already part of the WSU design and integration plan, this will greatly help the EHT get back to observing with ALMA and reach its ambitious goals in the WSU era.