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| How Do You Take a Picture of a Black Hole? With a Telescope as Big as the Earth | How Do You Take a Picture of a Black Hole? With a Telescope as Big as the Earth |
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| We live 26,000 light-years from the center of the Milky Way. That’s a rounding error by cosmological standards, but still — it’s far. When the light now reaching Earth from the galactic center first took flight, people were crossing the Bering Strait land bridge, hunting woolly mammoths along the way. | We live 26,000 light-years from the center of the Milky Way. That’s a rounding error by cosmological standards, but still — it’s far. When the light now reaching Earth from the galactic center first took flight, people were crossing the Bering Strait land bridge, hunting woolly mammoths along the way. |
| The distance hasn’t stopped astronomers from drawing a fairly accurate map of the heart of the galaxy. We know that if you travel inbound from Earth at the speed of light for about 20,000 years, you’ll encounter the galactic bulge, a peanut-shaped structure thick with stars, some nearly as old as the universe. Several thousand light-years farther in, there’s Sagittarius B2, a cloud a thousand times the size of our solar system containing silicon, ammonia, doses of hydrogen cyanide, at least ten billion billion billion liters of alcohol and dashes of ethyl formate, which tastes like raspberries. Continue inward for another 390 light-years or so and you reach the inner parsec, the bizarro zone within about three light-years of the galactic center. Tubes of frozen lightning called cosmic filaments streak the sky. Bubbles of gas memorialize ancient star explosions. Gravity becomes a foaming sea of riptides. Blue stars that make our sun look like a marble go slingshotting past at millions of miles per hour. Space becomes a bath of radiation; atoms dissolve into a fog of subatomic particles. And near the core, that fog forms a great glowing Frisbee that rotates around a vast dark sphere. This is the supermassive black hole at the core of the Milky Way, the still point of our slowly rotating galaxy. We call it Sagittarius A*, that last bit pronounced “A-star.” The black hole itself is invisible, but it leaves a violent imprint on its environment, pulling surrounding objects into unlikely orbits and annihilating stars and clouds of gas that stray too close. Scientists have long wondered what they would see if they could peer all the way to its edge. They may soon find out. | The distance hasn’t stopped astronomers from drawing a fairly accurate map of the heart of the galaxy. We know that if you travel inbound from Earth at the speed of light for about 20,000 years, you’ll encounter the galactic bulge, a peanut-shaped structure thick with stars, some nearly as old as the universe. Several thousand light-years farther in, there’s Sagittarius B2, a cloud a thousand times the size of our solar system containing silicon, ammonia, doses of hydrogen cyanide, at least ten billion billion billion liters of alcohol and dashes of ethyl formate, which tastes like raspberries. Continue inward for another 390 light-years or so and you reach the inner parsec, the bizarro zone within about three light-years of the galactic center. Tubes of frozen lightning called cosmic filaments streak the sky. Bubbles of gas memorialize ancient star explosions. Gravity becomes a foaming sea of riptides. Blue stars that make our sun look like a marble go slingshotting past at millions of miles per hour. Space becomes a bath of radiation; atoms dissolve into a fog of subatomic particles. And near the core, that fog forms a great glowing Frisbee that rotates around a vast dark sphere. This is the supermassive black hole at the core of the Milky Way, the still point of our slowly rotating galaxy. We call it Sagittarius A*, that last bit pronounced “A-star.” The black hole itself is invisible, but it leaves a violent imprint on its environment, pulling surrounding objects into unlikely orbits and annihilating stars and clouds of gas that stray too close. Scientists have long wondered what they would see if they could peer all the way to its edge. They may soon find out. |
| Astronomers found Sagittarius A* in 1974, when the notion of holes in space was still new and unsettling. Since then, they have probed it with every appropriate observational and theoretical instrument. Indirectly, they have weighed it, measured its girth, monitored its feeding habits. They now talk about it with measured confidence, like villagers describing a dragon that lives in a cave in the hills, an animal whose existence no one doubts, but which no one has ever seen. | Astronomers found Sagittarius A* in 1974, when the notion of holes in space was still new and unsettling. Since then, they have probed it with every appropriate observational and theoretical instrument. Indirectly, they have weighed it, measured its girth, monitored its feeding habits. They now talk about it with measured confidence, like villagers describing a dragon that lives in a cave in the hills, an animal whose existence no one doubts, but which no one has ever seen. |
| Of course, someone always mounts an expedition into the cave. Last year, after more than a decade of preparation, astronomers from North and South America, Europe and Asia made that metaphorical cave trip with the inaugural run of the Event Horizon Telescope (E.H.T.), a virtual Earth-size observatory designed to take the first picture of a black hole. The E.H.T. uses a technique known as very long baseline interferometry (V.L.B.I.), in which astronomers at observatories on different continents simultaneously observe the same object, then combine the collected data on a supercomputer. The E.H.T.’s director, Shep Doeleman, a radio astronomer with the Harvard-Smithsonian Center for Astrophysics, likes to call the E.H.T. “the biggest telescope in the history of humanity.” It has the highest resolution of any astronomical instrument ever assembled. It’s sharp enough to read the date on a nickel in Los Angeles from New York, to spot a doughnut on the moon and, more to the point, to take a picture of the black hole at the center of our galaxy — or, at least, its shadow. | Of course, someone always mounts an expedition into the cave. Last year, after more than a decade of preparation, astronomers from North and South America, Europe and Asia made that metaphorical cave trip with the inaugural run of the Event Horizon Telescope (E.H.T.), a virtual Earth-size observatory designed to take the first picture of a black hole. The E.H.T. uses a technique known as very long baseline interferometry (V.L.B.I.), in which astronomers at observatories on different continents simultaneously observe the same object, then combine the collected data on a supercomputer. The E.H.T.’s director, Shep Doeleman, a radio astronomer with the Harvard-Smithsonian Center for Astrophysics, likes to call the E.H.T. “the biggest telescope in the history of humanity.” It has the highest resolution of any astronomical instrument ever assembled. It’s sharp enough to read the date on a nickel in Los Angeles from New York, to spot a doughnut on the moon and, more to the point, to take a picture of the black hole at the center of our galaxy — or, at least, its shadow. |
| Astronomical images have a way of putting terrestrial concerns in perspective. Headlines may portend the collapse of Western civilization, but the black hole doesn’t care. It has been there for most of cosmic history; it will witness the death of the universe. In a time of lies, a picture of our own private black hole would be something true. The effort to get that picture speaks well of our species: a bunch of people around the world defying international discord and general ascendant stupidity in unified pursuit of a gloriously esoteric goal. And in these dark days, it’s only fitting that the object of this pursuit is the darkest thing imaginable. | Astronomical images have a way of putting terrestrial concerns in perspective. Headlines may portend the collapse of Western civilization, but the black hole doesn’t care. It has been there for most of cosmic history; it will witness the death of the universe. In a time of lies, a picture of our own private black hole would be something true. The effort to get that picture speaks well of our species: a bunch of people around the world defying international discord and general ascendant stupidity in unified pursuit of a gloriously esoteric goal. And in these dark days, it’s only fitting that the object of this pursuit is the darkest thing imaginable. |
| Avery Broderick, a theoretical astrophysicist who works with the Event Horizon Telescope, said in 2014 that the first picture of a black hole could be just as important as “Pale Blue Dot,” the 1990 photo of Earth that the space probe Voyager took from the edge of the solar system, in which our planet is an insignificant speck in a vast vacuum. A new picture, Avery thought, of one of nature’s purest embodiments of chaos and existential unease would have a different message: It would say, There are monsters out there. | |
| One of the many challenges of photographing a black hole is that they’re not “objects” in any familiar sense: They’re made of pure gravity. The standard definition of a black hole is “a region of space from which nothing, not even light, can escape,” but even that stark phrasing fails to capture their full demonic wonder. The physicist Werner Israel put it better when he described a black hole as “an elemental, self-sustaining gravitational field which has severed all causal connection with the material source that created it, and settled, like a soap bubble, into the simplest configuration consistent with the external constraints.” | One of the many challenges of photographing a black hole is that they’re not “objects” in any familiar sense: They’re made of pure gravity. The standard definition of a black hole is “a region of space from which nothing, not even light, can escape,” but even that stark phrasing fails to capture their full demonic wonder. The physicist Werner Israel put it better when he described a black hole as “an elemental, self-sustaining gravitational field which has severed all causal connection with the material source that created it, and settled, like a soap bubble, into the simplest configuration consistent with the external constraints.” |
| The defining feature of this gravitational soap bubble is its boundary, the event horizon, a one-way exit from the universe. If you were to cross an event horizon you would notice nothing. No turbulence. No shimmering diaphanous science-fiction membrane displaying memories from your childhood. But you could never return. The irreversibility of the event horizon is why black holes are, strictly speaking, unseeable: No light from within can ever reach the outside universe. But there are workarounds, cheats that can bring us asymptotically close. | The defining feature of this gravitational soap bubble is its boundary, the event horizon, a one-way exit from the universe. If you were to cross an event horizon you would notice nothing. No turbulence. No shimmering diaphanous science-fiction membrane displaying memories from your childhood. But you could never return. The irreversibility of the event horizon is why black holes are, strictly speaking, unseeable: No light from within can ever reach the outside universe. But there are workarounds, cheats that can bring us asymptotically close. |
| In 1973, the physicist James Bardeen figured out that in the right circumstances — if, say, a black hole passed in front of a large, bright background, like a star — it might be possible to see its silhouette. “Unfortunately,” Bardeen concluded, “there seems to be no hope of observing this effect.” Later that decade, the French physicist Jean-Pierre Luminet sought to learn what a black hole would look like if illuminated by the glow from the superheated matter swirling around it. He did his calculations by feeding punch cards into a primitive computer. He drew the results by hand. His black-and-white images looked like twisted depictions of a black Saturn, with a ringlike accretion disk warped like taffy. | In 1973, the physicist James Bardeen figured out that in the right circumstances — if, say, a black hole passed in front of a large, bright background, like a star — it might be possible to see its silhouette. “Unfortunately,” Bardeen concluded, “there seems to be no hope of observing this effect.” Later that decade, the French physicist Jean-Pierre Luminet sought to learn what a black hole would look like if illuminated by the glow from the superheated matter swirling around it. He did his calculations by feeding punch cards into a primitive computer. He drew the results by hand. His black-and-white images looked like twisted depictions of a black Saturn, with a ringlike accretion disk warped like taffy. |
| In the late 1990s, the astrophysicists Heino Falcke, Fulvio Melia and Eric Agol, motivated by a new generation of radio telescopes then under construction, decided to see whether there were any chance of seeing Sagittarius A*’s silhouette from Earth. They ran Bardeen’s equations through software that predicted how light would travel in the warped space-time around a black hole, and they concluded that with an Earth-size collection of radio telescopes, all of them operating at the highest frequencies of the radio spectrum, all of them simultaneously observing Sagittarius A*, one would see a dark circle ten times larger than the event horizon. At the edge of this circle, light rays would be trapped, tracing a glowing ring. Inside this ring, darkness. Sagittarius A* should cast a shadow. | In the late 1990s, the astrophysicists Heino Falcke, Fulvio Melia and Eric Agol, motivated by a new generation of radio telescopes then under construction, decided to see whether there were any chance of seeing Sagittarius A*’s silhouette from Earth. They ran Bardeen’s equations through software that predicted how light would travel in the warped space-time around a black hole, and they concluded that with an Earth-size collection of radio telescopes, all of them operating at the highest frequencies of the radio spectrum, all of them simultaneously observing Sagittarius A*, one would see a dark circle ten times larger than the event horizon. At the edge of this circle, light rays would be trapped, tracing a glowing ring. Inside this ring, darkness. Sagittarius A* should cast a shadow. |
| That this shadow might be visible from Earth depended on an astonishing set of circumstances. Earth’s atmosphere happens to be transparent to the electromagnetic radiation — in this case, certain microwaves — shining from the edge of the black hole, even though it blocks radiation of slightly longer and shorter wavelengths. The interstellar gunk lying between Earth and the galactic center also becomes transparent at those frequencies, as do the clouds of superheated matter just outside the black hole, blocking a view of the event horizon. Later in life, Fulvio Melia compared this alignment to the cosmic accidents that give us total solar eclipses. The moon is just the right size, in just the right orbit, at just the right distance from Earth that now and then it blocks the sun entirely. Fulvio wasn’t religious, but these coincidences were so unlikely that he couldn’t help but feel that the black-hole shadow was meant to be seen. The universe had arranged for humans to see to the nearest exit. | That this shadow might be visible from Earth depended on an astonishing set of circumstances. Earth’s atmosphere happens to be transparent to the electromagnetic radiation — in this case, certain microwaves — shining from the edge of the black hole, even though it blocks radiation of slightly longer and shorter wavelengths. The interstellar gunk lying between Earth and the galactic center also becomes transparent at those frequencies, as do the clouds of superheated matter just outside the black hole, blocking a view of the event horizon. Later in life, Fulvio Melia compared this alignment to the cosmic accidents that give us total solar eclipses. The moon is just the right size, in just the right orbit, at just the right distance from Earth that now and then it blocks the sun entirely. Fulvio wasn’t religious, but these coincidences were so unlikely that he couldn’t help but feel that the black-hole shadow was meant to be seen. The universe had arranged for humans to see to the nearest exit. |
| But the exit is poorly lit. Radio astronomers sometimes emphasize the difficulty of their jobs with the following fact: All the combined electromagnetic radiation collected by every radio telescope ever built, excluding that emitted by our own sun, would carry too little energy to melt a snowflake. To compensate for this scarcity — to collect as much energy as possible — astronomers build the biggest dishes they can. The world’s marquee radio telescopes are fearsome creations. The Robert C. Byrd Telescope in Green Bank, W.Va., is a full 120 feet taller than St. Paul’s Cathedral in London. But telescopes like that can’t handle microwaves. Few telescopes can. | But the exit is poorly lit. Radio astronomers sometimes emphasize the difficulty of their jobs with the following fact: All the combined electromagnetic radiation collected by every radio telescope ever built, excluding that emitted by our own sun, would carry too little energy to melt a snowflake. To compensate for this scarcity — to collect as much energy as possible — astronomers build the biggest dishes they can. The world’s marquee radio telescopes are fearsome creations. The Robert C. Byrd Telescope in Green Bank, W.Va., is a full 120 feet taller than St. Paul’s Cathedral in London. But telescopes like that can’t handle microwaves. Few telescopes can. |
| A radio telescope’s bowl-shaped reflecting surface — that giant glinting dish — is tiled with metal panels, each one polished to exacting specifications. To accurately reflect radio waves with a wavelength of one millimeter, for example, the panels must be free of bumps or scratches larger than one-twentieth of a millimeter. With enough money, you can make enormous reflecting surfaces that are smoother than this. But there is rarely enough money. | A radio telescope’s bowl-shaped reflecting surface — that giant glinting dish — is tiled with metal panels, each one polished to exacting specifications. To accurately reflect radio waves with a wavelength of one millimeter, for example, the panels must be free of bumps or scratches larger than one-twentieth of a millimeter. With enough money, you can make enormous reflecting surfaces that are smoother than this. But there is rarely enough money. |
| High-frequency radio waves create other challenges. The sharper a telescope’s resolution, the more accurately it must be aimed at its target. Accuracy isn’t simply a matter of being extra-careful when turning the knobs and dials. The entire multimillion-dollar electromechanical apparatus that swivels and steers the hulking instrument must be engineered to higher tolerances. Such precision is expensive, so most telescopes don’t have it. Big dishes also deform as they turn and tilt, and they expand and shrink and warp depending on the temperature and time of day. You can install thousands of independently tweakable, computer-controlled actuators that continuously adjust each surface panel, keeping the telescope in focus, but, again: expensive. For all these reasons, high-frequency radio telescopes tend to be small — generally, no larger than 10 meters in diameter. | High-frequency radio waves create other challenges. The sharper a telescope’s resolution, the more accurately it must be aimed at its target. Accuracy isn’t simply a matter of being extra-careful when turning the knobs and dials. The entire multimillion-dollar electromechanical apparatus that swivels and steers the hulking instrument must be engineered to higher tolerances. Such precision is expensive, so most telescopes don’t have it. Big dishes also deform as they turn and tilt, and they expand and shrink and warp depending on the temperature and time of day. You can install thousands of independently tweakable, computer-controlled actuators that continuously adjust each surface panel, keeping the telescope in focus, but, again: expensive. For all these reasons, high-frequency radio telescopes tend to be small — generally, no larger than 10 meters in diameter. |
| There is another problem. Yes, the earth’s atmosphere lets in the microwaves coming from the edge of the black hole, but earth’s weather can distort them as they travel through. A good site for a high-frequency radio telescope is somewhere high up and very dry, well into the zone where emergency oxygen tanks are required but flat enough to hold a structure the size of a Manhattan apartment building. If you have to ice-climb to the top, it won’t work: a road, however treacherous, should go to the summit. The site needs to be in a reasonably peaceful and friendly country where you can ship crates filled with atomic clocks and other sensitive equipment. | There is another problem. Yes, the earth’s atmosphere lets in the microwaves coming from the edge of the black hole, but earth’s weather can distort them as they travel through. A good site for a high-frequency radio telescope is somewhere high up and very dry, well into the zone where emergency oxygen tanks are required but flat enough to hold a structure the size of a Manhattan apartment building. If you have to ice-climb to the top, it won’t work: a road, however treacherous, should go to the summit. The site needs to be in a reasonably peaceful and friendly country where you can ship crates filled with atomic clocks and other sensitive equipment. |
| And, of course, to photograph a black hole, you need at least several dozen people with the right expertise to commit to years of grueling, frustrating work involving long, uncomfortable sojourns at remote mountaintop observatories. It wasn’t hard to find recruits. The project held plenty of allure for telescope builders and theorists alike: It was a historic engineering challenge in pursuit of a picture that might well be impossible. | And, of course, to photograph a black hole, you need at least several dozen people with the right expertise to commit to years of grueling, frustrating work involving long, uncomfortable sojourns at remote mountaintop observatories. It wasn’t hard to find recruits. The project held plenty of allure for telescope builders and theorists alike: It was a historic engineering challenge in pursuit of a picture that might well be impossible. |
| Shep Doeleman, the radio astronomer who willed the earliest incarnation of the Event Horizon Telescope into existence, is a wiry 51-year-old man of medium height with thin, chaotic brown hair and wire-frame glasses. He was 32 years old in 2000, when the Falcke-Fulvio-Melia paper came out, two years into a job running the high-frequency V.L.B.I. program at M.I.T.’s Haystack Observatory. He was closer to technical reality than most astronomers, so he had a good sense of what an experiment like this would take. And he knew it would be hard. | Shep Doeleman, the radio astronomer who willed the earliest incarnation of the Event Horizon Telescope into existence, is a wiry 51-year-old man of medium height with thin, chaotic brown hair and wire-frame glasses. He was 32 years old in 2000, when the Falcke-Fulvio-Melia paper came out, two years into a job running the high-frequency V.L.B.I. program at M.I.T.’s Haystack Observatory. He was closer to technical reality than most astronomers, so he had a good sense of what an experiment like this would take. And he knew it would be hard. |
| In the early 2000s, high-frequency radio observatories were under construction in Hawaii, Chile, Mexico and elsewhere, but when those observatories were complete they still wouldn’t be ready for this job, because they weren’t equipped to do very long baseline interferometry. The upgrade list varied from telescope to telescope, but in general, each site would need atomic clocks, for time-stamping data so it could later be combined with data from other telescopes; new signal-processing equipment and data recorders, which were still being designed; and invasive surgery to implant this new hardware. | In the early 2000s, high-frequency radio observatories were under construction in Hawaii, Chile, Mexico and elsewhere, but when those observatories were complete they still wouldn’t be ready for this job, because they weren’t equipped to do very long baseline interferometry. The upgrade list varied from telescope to telescope, but in general, each site would need atomic clocks, for time-stamping data so it could later be combined with data from other telescopes; new signal-processing equipment and data recorders, which were still being designed; and invasive surgery to implant this new hardware. |
| But Doeleman was an optimist and a romantic, and he saw that the same technological progress behind the iPod would soon transform high-frequency radio astronomy. Moore’s Law would usher into existence affordable, powerful off-the-shelf microprocessors and hard drives that could replace creaky hand-built signal-processing equipment and slow, finicky reels of magnetic tape. Faster processors and higher-capacity recorders would make it possible to collect more data with smaller dishes like the ones being built in Hawaii, Chile and beyond. | But Doeleman was an optimist and a romantic, and he saw that the same technological progress behind the iPod would soon transform high-frequency radio astronomy. Moore’s Law would usher into existence affordable, powerful off-the-shelf microprocessors and hard drives that could replace creaky hand-built signal-processing equipment and slow, finicky reels of magnetic tape. Faster processors and higher-capacity recorders would make it possible to collect more data with smaller dishes like the ones being built in Hawaii, Chile and beyond. |
| Even if every new high-frequency radio observatory in the world agreed to play along, the logistics were daunting. Everything would have to go right at every telescope in the array, or the whole thing would fail. They’d have to find a night when Sagittarius A* happened to be in the right position of the sky so that telescopes in Europe, North America, South America, Hawaii and the South Pole could all see it at the same time. On that night the skies would have to be clear in all of those places simultaneously. And every telescope they needed would have to stay in business long enough to get the picture, even though new telescopes coming online might put old ones out of business. | Even if every new high-frequency radio observatory in the world agreed to play along, the logistics were daunting. Everything would have to go right at every telescope in the array, or the whole thing would fail. They’d have to find a night when Sagittarius A* happened to be in the right position of the sky so that telescopes in Europe, North America, South America, Hawaii and the South Pole could all see it at the same time. On that night the skies would have to be clear in all of those places simultaneously. And every telescope they needed would have to stay in business long enough to get the picture, even though new telescopes coming online might put old ones out of business. |
| They still went for it. In 2007, after a failed attempt the previous year, Doeleman and a small crew set out to prove the concept, to see whether they could get a triangle of high-frequency radio telescopes in Hawaii, California and Arizona to detect Sagittarius A*. They spent a couple weeks on Mauna Kea, installing and testing borrowed equipment and waiting on the weather. On clear nights they’d stay up from well before dusk until after dawn, when they’d pack hard drives filled with billions of numbers representing noise and cosmic signal into foam crates. They’d draw straws to decide who had to drive the crates down to Hilo and FedEx them back to Haystack for correlation. At the end of the run, they dismantled their equipment and shipped it back East. Then they all went home. They had no idea whether the experiment had worked. | They still went for it. In 2007, after a failed attempt the previous year, Doeleman and a small crew set out to prove the concept, to see whether they could get a triangle of high-frequency radio telescopes in Hawaii, California and Arizona to detect Sagittarius A*. They spent a couple weeks on Mauna Kea, installing and testing borrowed equipment and waiting on the weather. On clear nights they’d stay up from well before dusk until after dawn, when they’d pack hard drives filled with billions of numbers representing noise and cosmic signal into foam crates. They’d draw straws to decide who had to drive the crates down to Hilo and FedEx them back to Haystack for correlation. At the end of the run, they dismantled their equipment and shipped it back East. Then they all went home. They had no idea whether the experiment had worked. |
| They didn’t have the telescopic power to make an image, but they saw something — a shape smaller than Sagittarius A*’s event horizon. It was a breakthrough. Nature published the results. Harvard and M.I.T. invited Doeleman to present his results. It was the moment of his arrival. | They didn’t have the telescopic power to make an image, but they saw something — a shape smaller than Sagittarius A*’s event horizon. It was a breakthrough. Nature published the results. Harvard and M.I.T. invited Doeleman to present his results. It was the moment of his arrival. |
| Together with his collaborators, Doeleman parlayed that first success into more telescope time. Each time they went out, they added some new capacity, reached some new goal, which they then wrote into the next year’s telescope-time applications and grant proposals. The incremental successes compounded. More like-minded scientists joined the team every year. In January 2012 the University of Arizona hosted a formal kickoff meeting for the E.H.T. in Tucson. The plan for the next three years was to expand the array from three stations to eight. The additional telescopes, along with new electronics they were developing, would enhance the sensitivity of the E.H.T. 40 times over. That, they believed, would be enough to get the first image of Sagittarius A*’s shadow. And they were just starting to realize how much that image might tell us. | Together with his collaborators, Doeleman parlayed that first success into more telescope time. Each time they went out, they added some new capacity, reached some new goal, which they then wrote into the next year’s telescope-time applications and grant proposals. The incremental successes compounded. More like-minded scientists joined the team every year. In January 2012 the University of Arizona hosted a formal kickoff meeting for the E.H.T. in Tucson. The plan for the next three years was to expand the array from three stations to eight. The additional telescopes, along with new electronics they were developing, would enhance the sensitivity of the E.H.T. 40 times over. That, they believed, would be enough to get the first image of Sagittarius A*’s shadow. And they were just starting to realize how much that image might tell us. |
| A close look at a black hole would be an obvious boon for scientists who study the origins and fates of stars and galaxies. Galaxies and their central black holes seem to evolve together. They go through stages. Sometimes the black hole spends eons inhaling matter as fast as physically possible, converting that matter into energy in a long-lasting cataclysm, each instant the equivalent of billions of thermonuclear weapons detonating simultaneously. In these “active” stages the black holes fire jets of matter and energy across the universe, landscaping the cosmos just as great rivers cleave continents and build deltas. Black holes decide when their host galaxies can grow new stars: When they’re on a rampage, sending out shock waves and howling cosmic winds, baby stars can’t grow. When a black hole settles down into a quiescent state, the next generation of stars gets to form. How and why these things happen is still a mystery, and the answers may lie near the event horizon. | A close look at a black hole would be an obvious boon for scientists who study the origins and fates of stars and galaxies. Galaxies and their central black holes seem to evolve together. They go through stages. Sometimes the black hole spends eons inhaling matter as fast as physically possible, converting that matter into energy in a long-lasting cataclysm, each instant the equivalent of billions of thermonuclear weapons detonating simultaneously. In these “active” stages the black holes fire jets of matter and energy across the universe, landscaping the cosmos just as great rivers cleave continents and build deltas. Black holes decide when their host galaxies can grow new stars: When they’re on a rampage, sending out shock waves and howling cosmic winds, baby stars can’t grow. When a black hole settles down into a quiescent state, the next generation of stars gets to form. How and why these things happen is still a mystery, and the answers may lie near the event horizon. |
| The edge of a black hole is also an ideal place to test the theory of general relativity, which scientists have been trying for the last century to break. General relativity describes the universe on the largest scales. Another, equally successful, equally unbreakable theory of nature has coexisted awkwardly alongside general relativity for a century: quantum theory. Quantum theory governs the subatomic world. General relativity and quantum theory both govern their respective domains perfectly. The problem is that they describe worlds that look nothing like each other. | The edge of a black hole is also an ideal place to test the theory of general relativity, which scientists have been trying for the last century to break. General relativity describes the universe on the largest scales. Another, equally successful, equally unbreakable theory of nature has coexisted awkwardly alongside general relativity for a century: quantum theory. Quantum theory governs the subatomic world. General relativity and quantum theory both govern their respective domains perfectly. The problem is that they describe worlds that look nothing like each other. |
| The two theories collide most violently in black holes. We say, for example, that Sagittarius A* is a four-million-solar-mass black hole, implying that the black hole “contains” four million suns’ worth of matter. But Einstein’s equations say that the interior of a black hole is a vacuum, and that all the matter that has ever fallen in is packed into an infinitely dense, infinitely small surface at the center of the black hole called a singularity. This doesn’t make much sense, and scientists know it. To understand what happens at the singularity, scientists need a theory of quantum gravity: a framework that unites general relativity with quantum theory. That theory may reveal what happens, or happened, at other singularities, including the one that begot our universe — the Big Bang. But it’s hard to reconcile two conflicting theories if you can’t find something wrong with either one, and quantum theory, like general relativity, has passed every test. As a result, scientists have been looking for ever-more-extreme situations in which to test these theories. That led them to black holes. | The two theories collide most violently in black holes. We say, for example, that Sagittarius A* is a four-million-solar-mass black hole, implying that the black hole “contains” four million suns’ worth of matter. But Einstein’s equations say that the interior of a black hole is a vacuum, and that all the matter that has ever fallen in is packed into an infinitely dense, infinitely small surface at the center of the black hole called a singularity. This doesn’t make much sense, and scientists know it. To understand what happens at the singularity, scientists need a theory of quantum gravity: a framework that unites general relativity with quantum theory. That theory may reveal what happens, or happened, at other singularities, including the one that begot our universe — the Big Bang. But it’s hard to reconcile two conflicting theories if you can’t find something wrong with either one, and quantum theory, like general relativity, has passed every test. As a result, scientists have been looking for ever-more-extreme situations in which to test these theories. That led them to black holes. |
| Scientists have spent years creating mathematical models and computer simulations that predict how Sagittarius A* will look when and if they see it. Models that assume general relativity is correct predict a circular shadow with an offset blob of orbiting superheated matter. If the E.H.T.’s results match these predictions, it will confirm that Einstein had space and time figured out more than a century ago. But if they don’t match — or if the shadow doesn’t appear at all — then things get really interesting. Any deviations would be evidence that Einstein’s equations are only an approximation of some deeper physical law. More than that, they would provide clues about the identity of that deeper law. And if scientists ever come to understand nature at its most fundamental, it would be, as Stephen Hawking once wrote, “the ultimate triumph of human reason — for then we should know the mind of God.” | Scientists have spent years creating mathematical models and computer simulations that predict how Sagittarius A* will look when and if they see it. Models that assume general relativity is correct predict a circular shadow with an offset blob of orbiting superheated matter. If the E.H.T.’s results match these predictions, it will confirm that Einstein had space and time figured out more than a century ago. But if they don’t match — or if the shadow doesn’t appear at all — then things get really interesting. Any deviations would be evidence that Einstein’s equations are only an approximation of some deeper physical law. More than that, they would provide clues about the identity of that deeper law. And if scientists ever come to understand nature at its most fundamental, it would be, as Stephen Hawking once wrote, “the ultimate triumph of human reason — for then we should know the mind of God.” |
| On five nights over a span of 10 days, teams at high-altitude observatories in France, Mexico, Chile, Arizona, Hawaii and the South Pole tracked Sagittarius A* through the night. When the inaugural E.H.T. observing run concluded on April 11, 2017, the astronomers had recorded more than 65 hours of data. They’d had good fortune all week: clear weather, no catastrophic failures. The astronomers at each of the eight participating observatories shipped a total of 1,024 eight-terabyte hard drives containing the observation’s harvest to Haystack Observatory and the Max Planck Institute for Radio Astronomy for correlation, and the drives all arrived in good condition. Then the correlator operators dove into the noise in search of signal, adjusting for the drift of the atomic clocks and the wobbles of Earth and tiny uncertainties in the positions of the telescopes. They stalked abstract mathematical spaces for correlations. And one by one, they found them. Every thread of the web was intact. Because they didn’t want to raise false hopes or encourage speculation, the collaborators were sworn to secrecy. | On five nights over a span of 10 days, teams at high-altitude observatories in France, Mexico, Chile, Arizona, Hawaii and the South Pole tracked Sagittarius A* through the night. When the inaugural E.H.T. observing run concluded on April 11, 2017, the astronomers had recorded more than 65 hours of data. They’d had good fortune all week: clear weather, no catastrophic failures. The astronomers at each of the eight participating observatories shipped a total of 1,024 eight-terabyte hard drives containing the observation’s harvest to Haystack Observatory and the Max Planck Institute for Radio Astronomy for correlation, and the drives all arrived in good condition. Then the correlator operators dove into the noise in search of signal, adjusting for the drift of the atomic clocks and the wobbles of Earth and tiny uncertainties in the positions of the telescopes. They stalked abstract mathematical spaces for correlations. And one by one, they found them. Every thread of the web was intact. Because they didn’t want to raise false hopes or encourage speculation, the collaborators were sworn to secrecy. |
| For more than a year they calibrated and corrected and reality-checked their data. Then in June, they released the final Sagittarius A* and M87 data to four small groups tasked with making images. Radio astronomers make images by feeding data about the radiation they have observed to algorithms that construct a picture of the object that emitted it. If the E.H.T. were an actual telescope the size of Earth, making images would be straightforward, the results unambiguous and direct. But because the E.H.T. is just a few specks of mirror on a rotating globe, an infinite number of possible images could explain any given data set. To be sure the images they extracted from their data depicted what was really up there in the sky, they installed checks and balances in the imaging process — hence the four separate groups. To avoid poisoning one another’s minds — so that no one could accidentally nudge another group into seeing a black-hole shadow that wasn’t really there — these groups worked in isolation, making images using different algorithms and techniques, trying hard to discredit anything that looked too sharp, too clean, too likely to be the product of wishful thinking. | For more than a year they calibrated and corrected and reality-checked their data. Then in June, they released the final Sagittarius A* and M87 data to four small groups tasked with making images. Radio astronomers make images by feeding data about the radiation they have observed to algorithms that construct a picture of the object that emitted it. If the E.H.T. were an actual telescope the size of Earth, making images would be straightforward, the results unambiguous and direct. But because the E.H.T. is just a few specks of mirror on a rotating globe, an infinite number of possible images could explain any given data set. To be sure the images they extracted from their data depicted what was really up there in the sky, they installed checks and balances in the imaging process — hence the four separate groups. To avoid poisoning one another’s minds — so that no one could accidentally nudge another group into seeing a black-hole shadow that wasn’t really there — these groups worked in isolation, making images using different algorithms and techniques, trying hard to discredit anything that looked too sharp, too clean, too likely to be the product of wishful thinking. |
| At some point within the next few months, the astronomers will finish their final analysis and submit their results to a scientific journal for peer review. If everything is in order, the results will be published, and then the world will see — something. | At some point within the next few months, the astronomers will finish their final analysis and submit their results to a scientific journal for peer review. If everything is in order, the results will be published, and then the world will see — something. |
| It’s possible we’ll encounter what Doeleman calls the nose-of-God scenario, in which an unmistakable image of the black hole shadow easily and quickly comes into focus. Or the picture could be muddy, confusing, subject to multiple interpretations. Maybe it will reveal something completely unexpected: After all, no one has ever seen a black hole. Even a pristine, searing image of the shadow of a black hole won’t end the story. Other scientists will pick apart the image and all the accompanying data. That’s how it goes. But even if no one immediately agrees on what the first picture tells us, its arrival could signal the beginning of a new era — with luck, one in which people gain new traction in the long and baffling quest to understand what happens in those dark places where space-time ends. | It’s possible we’ll encounter what Doeleman calls the nose-of-God scenario, in which an unmistakable image of the black hole shadow easily and quickly comes into focus. Or the picture could be muddy, confusing, subject to multiple interpretations. Maybe it will reveal something completely unexpected: After all, no one has ever seen a black hole. Even a pristine, searing image of the shadow of a black hole won’t end the story. Other scientists will pick apart the image and all the accompanying data. That’s how it goes. But even if no one immediately agrees on what the first picture tells us, its arrival could signal the beginning of a new era — with luck, one in which people gain new traction in the long and baffling quest to understand what happens in those dark places where space-time ends. |
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