The Event Horizon Telescope—a planet-scale array of eight ground-based radio telescopes forged through international collaboration—was designed to capture images of a black hole. On April 10, in coordinated news conferences across the globe, researchers reveal that they have succeeded, unveiling the first direct visual evidence of a supermassive black hole and its shadow.
This breakthrough was announced April 10 in a series of six papers published in a special issue of The Astrophysical Journal Letters. The image reveals the black hole at the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole sits 55 million light-years from Earth and has a mass 6.5 billion times that of the sun.
The EHT links telescopes around the globe, including the University of Chicago-run South Pole Telescope, to form an unprecedented Earth-sized “virtual telescope” with unprecedented sensitivity and resolution. The EHT is the result of years of international collaboration, and offers scientists a new way to study the most extreme objects in the universe predicted by Einstein’s theory of general relativity.
“We have taken the first picture of a black hole—a one-way door out of our universe,” said EHT project director Sheperd S. Doeleman of the Center for Astrophysics | Harvard & Smithsonian. “This is an extraordinary scientific feat accomplished by a team of more than 200 researchers.”
Black holes are extraordinary cosmic objects with enormous masses but extremely compact sizes. The presence of these objects affects their environment in extreme ways, warping spacetime and super-heating any surrounding material.
“If immersed in a bright region, like a disc of glowing gas, we expect a black hole to create a dark region similar to a shadow—something predicted by Einstein’s general relativity that we’ve never seen before,” explained chair of the EHT Science Council Heino Falcke of Radboud University in the Netherlands. “This shadow, caused by the gravitational bending and capture of light by the event horizon, reveals a lot about the nature of these fascinating objects and has allowed us to measure the enormous mass of M87’s black hole.”
Multiple calibration and imaging methods have revealed a ring-like structure with a dark central region—the black hole’s shadow—that persisted over multiple independent EHT observations.
The EHT observations use a technique called very-long-baseline interferometry, which synchronizes eight telescope facilities around the world and exploits the rotation of our planet to form one huge, Earth-size telescope observing at a wavelength of 1.3mm. This technique allows the EHT to achieve an angular resolution of 20 micro-arcseconds—enough to read a newspaper in New York from a sidewalk café in Paris.
One of these telescopes was the South Pole Telescope, one of the most sensitive instruments in the world built to search for the oldest light in the universe. Operated by an international collaboration led by the University of Chicago, the South Pole Telescope helped calibrate the data from all telescopes and is key to expanding the EHT’s reach around the globe.