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How Do You Take a Picture of a Black Hole? with a Telescope As Big As the Earth

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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 A planet-spanning virtual observatory, years in the making, could change how we think about space, time and the nature of reality. Will it work? By Seth Fletcher Oct. 4, 2018 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. 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. Please disable your ad blocker. Advertising helps fund Times journalism. Unblock ads 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 rings of Saturn, 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. You have 4 free articles remaining. Subscribe to The Times 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. Please disable your ad blocker. Advertising helps fund Times journalism. Unblock ads 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. 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.
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