Astronomers using the Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes (ALMA, APEX, the IRAM 30-m telescope, the James Clerk Maxwell Telescope, the Large Millimeter Telescope Alfonso Serrano, the Submillimeter Array, the Submillimeter Telescope, and the South Pole Telescope) — have obtained the first image of a black hole, using EHT observations of the center of Messier 87, a giant elliptical galaxy located some 53 million light-years from us in the constellation Virgo. This breakthrough was announced today in a series of six papers published in a special issue of the Astrophysical Journal Letters.
The EHT Collaboration unveiled the first direct visual evidence of the supermassive black hole in the center of the elliptical galaxy Messier 87 and its shadow. The shadow of a black hole seen here is the closest we can come to an image of the black hole itself, a completely dark object from which light cannot escape. The black hole’s boundary — the event horizon from which the EHT takes its name — is around 2.5 times smaller than the shadow it casts and measures just under 25 billion miles (40 billion km) across. Image credit: EHT Collaboration.
Black holes are extremely dense pockets of matter, objects of such incredible mass and miniscule volume that they drastically warp the fabric of space-time. Anything that passes too close, from a wandering star to a photon of light, gets captured.
Most black holes are the condensed remnants of a massive star, the collapsed core that remains following an explosive supernova.
However, the black hole family tree has several branches, from tiny structures on par with a human cell to enormous giants billions of times more massive than our Sun.
“If immersed in a bright region, like a disk 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,” said Radboud University astronomer Dr. Heino Falcke, chair of the EHT Science Council.
“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 allowed us to measure the enormous mass of the central black hole of Messier 87.”
According to the EHT team, the enormous black hole in the center of Messier 87 has a mass of approximately 6.5 billion solar masses.
Multiple calibration and imaging methods revealed a ring-like structure with a dark central region — the black hole’s shadow — that persisted over multiple independent EHT observations.
“Once we were sure we had imaged the shadow, we could compare our observations to extensive computer models that include the physics of warped space, superheated matter and strong magnetic fields,” said Dr. Paul T.P. Ho, EHT Board member and Director of the East Asian Observatory.
“Many of the features of the observed image match our theoretical understanding surprisingly well.”
“This makes us confident about the interpretation of our observations, including our estimation of the black hole’s mass.”
The EHT observations use a technique called very-long-baseline interferometry (VLBI) which synchronizes telescope facilities around the world and exploits the rotation of our planet to form one huge, Earth-size telescope observing at a wavelength of 1.3 mm.
VLBI allows EHT to achieve an angular resolution of 20 micro-arcseconds — enough to read a newspaper in New York from a sidewalk café in Paris.
“We have taken the first picture of a black hole,” said EHT project director Dr. Sheperd S. Doeleman, from the Center for Astrophysics at Harvard & Smithsonian.
“This is an extraordinary scientific feat accomplished by a team of more than 200 researchers.”
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Event Horizon Telescope Collaboration et al. 2019. First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole. ApJL 875, L1; doi: 10.3847/2041-8213/ab0ec7
Event Horizon Telescope Collaboration et al. 2019. First M87 Event Horizon Telescope Results. II. Array and Instrumentation. ApJL 875, L2; doi: 10.3847/2041-8213/ab0c96
Event Horizon Telescope Collaboration et al. 2019. First M87 Event Horizon Telescope Results. III. Data Processing and Calibration. ApJL 875, L3; doi: 10.3847/2041-8213/ab0c57
Event Horizon Telescope Collaboration et al. 2019. First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole. ApJL 875, L4; doi: 10.3847/2041-8213/ab0e85
Event Horizon Telescope Collaboration et al. 2019. First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring. ApJL 875, L5; doi: 10.3847/2041-8213/ab0f43
Event Horizon Telescope Collaboration et al. 2019. First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole. ApJL 875, L6; doi: 10.3847/2041-8213/ab1141
