At the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster, exists a supermassive black hole. Dubbed M87, this all-consuming region of spacetime is located more than 55 million light-years from Earth and is estimated to have a light-sucking core 6.5 billion times the mass of the sun.
For the first time, we have an "image" of this celestial monster, and it even has a name: Powehi, which means "adorned fathomless dark creation." The striking name was a collaborative effort between astronomers and University of Hawaii language professor Larry Kimura.
"This is a huge day in astrophysics," NSF Director France Córdova said in a statement. "We're seeing the unseeable. Black holes have sparked imaginations for decades. They have exotic properties and are mysterious to us. Yet with more observations like this one they are yielding their secrets. This is why NSF exists. We enable scientists and engineers to illuminate the unknown, to reveal the subtle and complex majesty of our universe."
As Manchester University astronomer Tim Muxlow told The Guardian in 2017, the image captured isn't exactly a direct photo of a black hole as much as it's a picture of its shadow.
"It will be an image of its silhouette sliding against the background glow of radiation of the heart of the Milky Way," he said. "That photograph will reveal the contours of a black hole for the first time."
The giant elliptical galaxy Messier 87 appears on this very deep image. A photo of the supermassive black hole at the heart of this galaxy was recently captured by an international team of researchers. (Photo: Chris Mihos, Case Western Reserve University/ESO/Wikimedia)
Despite its supermassive size, M87 is far enough away from us to present a massive challenge for any one telescope to capture. According to Nature, it would require something with a resolution more than 1,000 times better than the Hubble Space Telescope to pull off. Instead, astronomers decided to create something bigger –– much bigger.
In April 2018, astronomers synchronized a global network of radio telescopes to observe the immediate environment of M87. Together, like the fictional robot character Voltron, they combined to form the Event Horizon Telescope (EHT), a virtual planet-sized observatory capable of capturing unprecedented detail over great distances.
"Instead of building a telescope so big that it would probably collapse under its own weight, we combined eight observatories like the pieces of a giant mirror," Michael Bremer, an astronomer at the International Research Institute for Radio Astronomy (IRAM) and a project manager for the Event Horizon Telescope, is quoted as saying at the time. "This gave us a virtual telescope as big as Earth — about 10,000 kilometres (6,200 miles) in diameter."
It takes a village (of telescopes)
Over several days, locked to each other using the exceptional precision of atomic clocks, the radio telescopes captured an enormous amount of data on M87.
According to European Southern Observatory, its Atacama Large Millimeter/submillimeter Array (ALMA), a participating partner in the Event Horizon Telescope, alone recorded over a petabyte (1 million gigabytes) of information on the black hole. Too large to send over the Internet, the physical hard drives were sent via plane and input into computing clusters (called a correlator) located at the MIT Haystack Observatory in Cambridge, Massachusetts, and the Max Planck Institute for Radio Astronomy in Bonn, Germany.
And then the researchers waited. The first obstacle on the road to processing an image involved the eighth participating radio telescope stationed in Antarctica. Because no flights are possible from February to October, the final data set captured by the South Pole Telescope was literally placed in cold storage. On Dec. 13, 2017, it finally arrived at the Haystack Observatory.
"After the disks have warmed up, they will be loaded into playback drives and processed with data from the other 7 EHT stations to complete the Earth-sized virtual telescope that links dishes from the South Pole, to Hawaii, Mexico, Chile, Arizona, and Spain," the team announced in December 2017. "It should take about 3 weeks to complete the comparison of recordings, and after that the final analysis of the 2017 EHT data can begin!"
That final analysis stretched through all of 2018, with the 200-strong research team carefully studying the collected data and accounting for any error sources (turbulence in the Earth's atmosphere, random noise, spurious signals, etc.) that might degrade the event horizon image. They also had to develop and test new algorithms to convert the data into "maps of radio emissions on the sky."
As Shep Doeleman, director of the EHT, said in a May 2018 update, the process has been so labor-intensive that astronomers have taken to calling it the "ultimate in delayed gratification."
According to the NSF, the data collected measured more than 5 petabytes and consisted of over a half-ton of hard drives.
Einstein's General Relativity passes another big test
According to the researchers, the shape of the black hole's shadow yet another aspect of Einstein's Theory of General Relativity.
"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, 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 allowed us to measure the enormous mass of M87's black hole."
Now that the image has been revealed, it existence is likely to only deepen the questions and awe surrounding these mysterious astronomical phenomena. The sheer engineering alone that has given rise to this historical moment is reason enough to celebrate.
"We have achieved something presumed to be impossible just a generation ago," EHT project director Sheperd S. Doeleman of the Center for Astrophysics | Harvard & Smithsonian said. "Breakthroughs in technology, connections between the world's best radio observatories, and innovative algorithms all came together to open an entirely new window on black holes and the event horizon."
Editor's note: This article has been updated with new information since it was first published in January 2018.