Frontier Science with the Event Horizon Telescope

This award supports one year of continued operations of the Event Horizon Telescope (EHT) as a facility for frontier science, leveraging extensive NSF and international investment. Initially conceived as an instrument to produce images of supermassive black holes (SMBH), recent upgrades allow the EHT to explore the dynamics of accretion and outflow around black holes using time-lapse monitoring. New operating modes that will increase open access to the EHT will be tested. EHT has seen significant increases in capability by deploying new telescopes and receivers, developing advanced analysis and imaging algorithms, and enhancing observing agility. The EHT Collaboration (EHTC) also provides analysis and imaging tools and calibration information to help both key black-hole dynamics studies and PI-led projects. Training of junior scientists is foundational to the EHTC, as they have essential roles in telescope operations, data calibration, and knowledge generation. Undergraduates work on related projects. The public response to the first shadow images shows their enduring fascination with black holes and the extraordinary outreach potency of the EHT. Public dissemination and outreach will continue. The EHT is a network of (sub)millimeter telescopes that uses the technique of very long baseline interferometry (VLBI) to achieve the sharpest angular resolution of any current astronomical instrument. Primary science drivers include determining the origin of relativistic jets, testing the spin extraction hypothesis, understanding flares, and characterizing the population of SMBH in galactic nuclei. Dynamical multi-wavelength observations of the black hole in our Galactic center (Sgr A*) will probe flares and address why Sgr A* exhibits weaker variability than predicted by relativistic modeling. New spectral-line VLBI capabilities will enable studies of submillimeter masers and molecular absorption lines at higher resolution than presently possible. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.