An International Team of Astronomers Has Produced the First Ever Image of a Black Hole
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BREAKTHROUGH NEWS 2019 of the YEAR EMBARGOED UNTIL 2:00PM US ET, THURSDAY 19 DECEMBER 2019 An international team of astronomers has produced the first ever image of a black hole By Daniel Clery 3 PEOPLE’S CHOICE assive, ubiquitous, and in some For astronomers, the image is a validation cases as big as our Solar Sys- of decades of work theorizing about esoteric tem, black holes hide in plain objects they couldn’t see. “I’m still kind of sight. The effect of their gravity stunned,” says astrophysicist Roger Blandford on objects around them and, of Stanford University in Palo Alto, Califor- lately, the gravitational waves nia. “I don’t think any of us imagined the emitted when they collide re- iconic image that was produced.” In fact, un- veal their presence. But no one til recently few astronomers imagined such had ever seen one directly—un- an image was even possible. Black holes are til April. That’s when an international team very small by cosmic standards and by defi- Mof radio astronomers released a startling nition emit no light. When they grow to gar- close-up image of a black hole’s “shadow,” gantuan masses, as happens in the centers of showing a dark heart surrounded by a ring galaxies, the swirling mayhem of gas, dust, of light created by photons zipping around and stars stirred up by their extreme gravity it. Heino Falcke of Radboud University in creates an additional barrier. Nijmegen, the Netherlands, a member of But 2 decades ago, a handful of astrono- the team that produced the image, said the mers began to wonder whether the hot first glimpse felt like “looking at the gates of swirling gases close to a giant black hole’s hell.” That evocative image is Science’s 2019 The iconic image of galaxy Messier 87’s central black edge, or event horizon, might make it visible. Breakthrough of the Year. hole, showing a ring of photons bent by its gravity. They glow at many wavelengths including OZEL/ PSALTIS/FERYAL CHAN/DIMITRIOS MEDEIROS/CHI-KWAN LIA BOTTOM) TO (TOP IMAGES: 4.0 COLLABORATION/CC EHT STUDY; ADVANCED FOR ARIZONA/INSTITUTE OF UNIVERSITY 1434 20 DECEMBER 2019 • VOL 366 ISSUE 6472 sciencemag.org SCIENCE EMBARGOED UNTIL 2:00PM US ET, THURSDAY 19 DECEMBER 2019 A simulation of matter swirling around the black hole the engine of this $1.5 billion U.S.-European- at the center of Messier 87 and radiating at different Japanese collaboration took years of persua- wavelengths. A bright ring of light orbiting the black sion and several rejected designs, but adding PEOPLE’S CHOICE hole’s shadow shines through the haze, and green ALMA boosted EHT’s sensitivity 10-fold. Our readers weigh in with their picks tendrils of a powerful jet stream from its pole. In April 2017, everything was in place for a for the top breakthrough of 2019 major 10-night observing run. ALMA, along millimeter waves—short-wavelength radio with seven other observatories in the United For readers of Science online, this waves—that can pierce the gas and dust sur- States, Mexico, Chile, Spain, and at the South was the year of the Denisovans. The rounding a galactic center. Developments in Pole, took repeated nightlong exposures of ancient humans had been known technology promised to help. A technique both Sgr A* and M87*. “We lucked out with only from scraps of fossils found in known as very-long-baseline interferometry the weather,” says EHT’s founding director a cave in Siberia in Russia. But this (VLBI), which combines data from widely Shep Doeleman of the Harvard-Smithsonian year, researchers used evidence from spaced radio dishes to simulate a much Center for Astrophysics in Cambridge, Mas- proteins to identify a fossilized jaw from larger telescope, was revealing distant ob- sachusetts. But it would be almost 2 years be- China’s Tibetan Plateau as Denisovan, jects in finer detail. And improvements in fore the EHT team knew what, if anything, it indicating they were widespread, receivers, antenna design, and had achieved. and genetic evidence to reconstruct digital electronics were allow- ON OUR WEBSITE Working in parallel at data cen- the face of a Denisovan girl. Those ing radio astronomers to capture ters in Germany and the United achievements are this year’s People’s For more on the millimeter waves. By observing at Breakthrough of States, separate teams calibrated Choice for Breakthrough of the Year. those wavelengths, using dishes the Year, including and processed the data, using sev- We invited visitors to Science’s spread as far apart as possible to a video and a eral different methods, while other website to vote on 12 candidates for the boost resolution, could they make podcast, go to: teams independently checked the breakthrough. A first round of voting https://scim.ag/ out the details of a black hole? Breakthrough2019 results. No image was produced narrowed the choices to four, and a Maybe, if it were a monster with until the very end, to avoid bias- second round, in which more than the mass of millions of suns, and relatively ing the outcome. The teams began to work 34,000 votes were cast, determined close by. The 4-million-solar-mass black hole on Sgr A* and M87* in parallel, but focused the People’s Choice. The Denisovan at the center of our Milky Way Galaxy, known on M87* when they found that the material research was the clear winner, followed as Sagittarius A* (Sgr A*), was an obvious swirling around Sgr A* changed by the hour, by the development of two promising contender, being the closest to Earth at just blurring the image. The action around the gi- drugs to treat Ebola, the first ever 26,000 light-years away. Despite its heft, it is ant M87* moves at a stately pace, changing image of a black hole—Science’s a tiny object in galactic terms—it would fit little over the course of a night. In April, the choice—and the development of a inside the orbit of Mercury—and imaging it team revealed an image of M87*. The black treatment for the majority of cystic would push VLBI to the limit. hole’s silhouette—outlined in a ring of light— fibrosis patients. The complete results: Early attempts about a dozen years ago adorned front pages and news reports across 1 Denisovans come into focus using telescopes in Hawaii and the main- the globe, and became the most downloaded 49% land United States revealed scraps of detail image in the history of the National Science 2 Ebola drugs 25% of the swirling superheated gas close to Sgr Foundation’s website. A description of the ef- A*. The telescopes also got a glimpse of a fort and its implications filled six papers in 3 Black hole image 15% second potential target: the supermassive Astrophysical Journal Letters. 4 Cystic fibrosis drug black hole at the center of the nearby gal- For black hole theorists, that first, rather 11% axy Messier 87. Although M87 is 2000 times blurry image sprang few surprises, but just farther from Earth than Sgr A*, its black seeing it was “a glorious affirmation of the- hole, M87*, has more than 1000 times the ory,” Blandford says. Albert Einstein’s de- EHT has 11 facilities lined up for the next mass so it appears roughly the same size scription of gravity, general relativity, predicts round of observing in 2020, including new in the sky. With observations beginning to a black hole’s shadow should be perfectly dishes in Greenland and Arizona and an bear fruit, funding agencies started to chip round—a prediction confirmed to within 10% upgraded array in France. Observations will in, and the international Event Horizon by the M87* image. That may rule out a few soon move to even shorter wavelengths— Telescope (EHT) was born. of the wildest alternative theories of gravity 0.86 millimeters instead of the 1.3 millimeters Despite its name, EHT is not a telescope that aim to supplant relativity, but the EHT used so far. Further in the future, the team but a consortium involving more than team will need to squeeze down the error hopes to add a dozen or so purpose-built 200 scientists from across the globe. It ap- bars in future observations to put Einstein to dishes scattered across the globe and some in plies for time on existing telescopes—as more stringent tests. space, to increase the resolution still further. A many and as widely spaced as possible. At The best tests of general relativity could dish one-third of the way to the Moon, for ex- most telescopes, EHT members must install come from an image of Sgr A*, which the ample, would bring another 20 supermassive their own equipment, including high data team hopes to finish in 2020. Researchers black holes into imaging range. rate digital processors and atomic clocks, have much more precise data on the mass, Such expansion would also enable EHT to to make the instrument VLBI-friendly. A size, and distance of Sgr A* than of M87*. graduate from making still images to “mov- turning point came when EHT enlisted the “That will immediately improve the quality ies” of a black hole sucking in material and Atacama Large Millimeter/submillimeter of constraints [on general relativity],” says funneling it into high-powered jets that fire Array (ALMA). Made up of 66 dishes high team member Feryal Özel of University of from its poles millions of light-years into in the desert mountains of northern Chile, Arizona in Tucson.