The Event Horizon Telescope: Resolving Black Holes in Time and Space

Black holes are the most mysterious objects in the cosmos. They are formed when matter collapses in on itself under the force of gravity, producing a singularity of infinite density. This singularity cannot be directly observed because it is surrounded by an event horizon, the point where the black hole’s gravitational field is so strong that even light cannot escape, but matter outside the event horizon can in principle be observed.

On April 10, 2019, the Event Horizon Telescope (EHT) succeeded in producing the first image of a black hole at the center of the galaxy M87, 55 million light years from Earth. The observed ring of light bent in the immense gravity was stunning confirmation that supermassive black holes exist in the centers of galaxies. The EHT results enabled scientists to verify key predictions of Einstein’s theory of gravity at the black hole boundary and to study how supermassive black holes dominate the energetics and dynamics at the centers of galaxies.

This project aims to build upon this success by improving the EHT so that astronomers can make black hole images that are much more detailed and take the first steps towards making black hole movies. Observations under this award will address key questions about general relativity and astronomy, including whether black holes spin and how they launch powerful jets that travel at nearly the speed of light to distances larger than the host galaxy itself.

This project includes resources for training the next generation of radio astronomers involving postdoctoral scholars and graduate and undergraduate students at US universities, including minority-serving institutions, and will undertake cultural outreach to the Hawaiian community.

This award supports continued operations of an enhanced Event Horizon Telescope (EHT) over the next three years to test general relativity and study the astrophysics of supermassive black holes, including the Galactic Center source (Sagittarius A*) and the black hole in the center of the nearby galaxy M87. Investments in instrumentation to transform submillimeter VLBI into a standard observing mode across the heterogeneous array will enable monitoring campaigns triggered during optimal observing conditions, allowing a study of the dynamics of the material at the base of the jet in M87.

The extension of observing to the 345 GHz frequency band will increase the angular resolution of the EHT, sharpen its view of Sagittarius A* due to reduced interstellar scattering, enhance its ability to study the structure of the magnetic field in these and other sources, and test the prediction that photon rings are independent of observing frequency. The EHT will continue to be made available to the broader astronomical community through an annual call for proposals.

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.