Event Horizon Telescope
The Event Horizon Telescope (EHT) is an experiment that is being performed on a large and ever-increasing array of radio telescopes that span the Earth from Hawaii to Chile and from the South Pole to Greenland. Its goal is to study black holes through imaging at very high spatial resolution. The main goal of the EHT is to image the event horizons of supermassive black holes, with an unprecedented 10-microarcsecond resolution.
The detection of a black-hole shadow provides the most direct evidence for a supermassive black hole in the Universe and allows us to test the detailed predictions of the theory of General Relativity. Because the size of the shadow is related to the mass of the black hole, this image allowed us to infer that the black-hole mass in M87 is approximately 6 billion times the mass of the Sun.
In addition to allowing us to test the theory of gravity in regimes where it has never been tested before, the EHT also enables us to study the process by which black holes accrete matter and grow in mass. It helps us answer questions about why some black holes launch giant well-collimated jets and others do not.
Credit: CK Chan
In April 2019, the EHT collaboration released the first ever picture of a supermassive black hole, the one at the center of the galaxy M87. This image shows a bright ring of emission surrounding the shadow that is cast by the black hole.
Credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScIs
The second primary target for the EHT is the supermassive black hole at the center of our Galaxy, Sagittarius A*. The first results for Sgr A* are expected in the near future. The EHT also has numerous other accreting black-hole targets that it studies at scales that are of the order of 10-100 times the size of their horizons.