The Event Horizon Telescope captured an image of a supermassive black hole last spring and revealed one of the darkest and most elusive phenomena in the known universe. The feat, once considered impossible, is being honored by Science's news and editorial team as its 2019 Breakthrough of the Year .
"This was a great year for science, but what could be more wondrous than actually seeing a black hole?" said Tim Appenzeller, the lead editor for Science's news section. "It sounds like magic, but it was really an astonishing feat of teamwork and technology."
The global reaction to this image, following its announcement on April 10, 2019, created an impression that surprised Shep Doeleman, founding director of Event Horizon Telescope (EHT), the consortium of more than 200 international scientists who obtained the image.
"It was only when we came down from our hotel rooms on April 11 and saw the black hole image on the front page of all the major newspapers that we realized our work had impact far beyond our team and other scientists," said Doeleman. "In retrospect, the global reaction makes sense; we captured an image of the most mysterious object in the cosmos, and we did it by creating an international team that turned the Earth itself into a planet-sized telescope. I think many people marveled at what humanity could do by working together in an age when so many issues tend to divide us."
Members of the EHT consortium that Doelman leads apply for time on existing telescopes — as many and as widely spaced as possible. At most telescopes, EHT members must install their own equipment, including high data rate digital processors and atomic clocks.
Black holes are immensely dense cosmic objects with gravity so strong that they capture and consume everything surrounding them, including light. Because of this, they often hide in plain sight, perfectly camouflaged against the inky black of the void. While evidence for their existence has been recognized for decades, no one had ever seen one directly.
Before EHT was established in 2009, earlier attempts to image black holes about a dozen years ago focused on the void at the center of our Milky Way Galaxy, known as Sagittarius A*. These efforts did not pan out but they did reveal a second potential target: the supermassive black hole at the center of the nearby galaxy Messier 87 (M87). This is the black hole EHT illuminated.
For their work that led to the image, a turning point came when EHT enlisted the most complex astronomical observatory ever built, the Atacama Large Millimeter/submillimeter Array (ALMA). Set high in the desert mountains of northern Chile, with 66 satellite dishes, it is by far the largest observatory at millimeter wavelengths. It can detect very tiny waves of light radiating through space, at millimeter and even submillimeter wavelengths.
Using it boosted EHT's imaging sensitivity analyses tenfold and imaging the cloud of hot, brightly glowing gas that surrounds M87, the EHT team was able to capture the silhouette of the super massive black hole that lies at its center.
The research is a validation of decades of work studying esoteric objects that astronomers couldn't see.
"I'm still kind of stunned," said Roger Blandford, a Stanford University astrophysicist. "I don't think any of us imagined the iconic image that was produced."
Obtaining the image was also an affirmation of Albert Einstein's theory of gravity, general relativity, which predicts a black hole's shadow should be perfectly round — a prediction confirmed to within 10% by the image of the black hole at M87's center.
The sight of the distant stellar object captured the minds and imaginations of people worldwide — from front-page international news stories to internet memes — and quickly became the most downloaded image in the history of the National Science Foundation's website.
"The image of the event horizon of the supermassive black hole in the nearby galaxy Messier 87 was a magnificent technical achievement and a worthy Breakthrough of the Year. But it is more than that," writes Science Editor-in-Chief, Holden Thorp, in an accompanying Editorial in Science. "For a skeptical public that often rolls their eyes when they hear scientists say that they know things exist even though they cannot be seen, this is one more important object that we can see."
Doeleman said the journey to get this end result was thrilling. "During most of the project, I was fixated on the concrete goal of making the image and measuring the black hole silhouette, but at the end, it was assembling the global team and coordinating the efforts of many, many talented people that meant the most to me. The EHT is not just an array of radio dishes; it is also an amazing group of very dedicated people."
Plans are underway for more observations with even greater resolution, including turning our eyes toward Sagittarius A*. "This year's triumph is the beginning, not the culmination, of this research project," said Blandford.
Each year, Science's reporters and editors choose the Breakthrough by reviewing the year's most significant and noteworthy scientific developments and discoveries. Through a separate Reader's Choice poll, the public also voted on its favorite science breakthrough. This year, Science readers declared the study that put us face-to-face with our ancient Denisovan human ancestors as their winner for 2019. Using a new method of analyzing ancient proteins in a 160,000-year-old jaw bone to trace chemical modifications of long-gone DNA, researchers were able to reconstruct the face of a Denisovan girl from Siberia. The study was also a Breakthrough runner-up voted by the journal's editors and news team.
Other runners-up include a wide range of scientific topics — from the earliest life on Earth to planet-altering cosmic-collisions. Among them is a milestone achievement in the realm of gene-based drugs — the development of an effective treatment for most cases of cystic fibrosis. The triple-drug combination corrects the effects of the most common mutation behind the disease and turns the progressive disease into a more manageable chronic illness. The achievement is the culmination of 30 years of research since the cystic fibrosis gene, CFTR, was first discovered and published in the pages of Science.
Science also named "Breakdowns" of the year. They include the growing divide between the public's increasing acceptance of climate change and continued political inaction; findings that show an almost 30% drop in the number of North American birds — nearly 3 billion fewer — since 1970; the resurgence of measles worldwide as vaccine misinformation continues to spread; and the burning of vast tracts of the Amazon due to forest fires sparked in part by the anti-environmental policies of Brazil's new president, Jair Bolsonaro.
[Credit for associated black hole illustration: Nicolle R. Fuller/NSF]