Science

July 23, 2012

Signals From the Void

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Even without a telescope, it’s possible to look off the summit of Mauna Kea and see, 14,000 feet below and dozens of miles in the distance, wide swaths of rain forest touching the whitecapped Pacific. Down there, people are doing what people come to Hawaii to do: hiking to waterfalls, lying in the sand, exposing their skin to tropical solar radiation. Up here, there is no vegetation, no warmth and very little atmosphere. And as the sun sets over the parabolic aluminum dishes of the Submillimeter Array observatory, it’s time to work.

Sheperd Doeleman, the 45-year-old MIT researcher in charge of tonight’s experiment, is setting up a piece of the radio telescope that, if all goes well, will synchronize with other radio telescopes in California and Arizona to observe matter on the verge of disappearing into a black hole. Doeleman and his counterparts on the mainland are using a technique called very long baseline interferometry to simulate a much larger instrument, which they call the Event Horizon Telescope. The longer the baseline, the higher the resolution, so these astronomers have for the past decade or so been hauling their delicate and expensive hand-built equipment to remote sites around the world, installing it anew for each observation. The work is highly improvisational, but to see what they want to see, there is no other way.

Outside the Submillimeter Array’s control-room windows, patches of snow speckle the summit. The storm that deposited them several days ago has since traveled 2,500 miles east, where it has been blocking all observation at the station in California, thus delaying the whole observing run. Things are going better tonight. Or at least they’re starting to. “It looks like we’re actually recording something,” Doeleman says. “Which is nice.”

“The Mark 5Bs are recording,” says Nicolas Pradel, a post­doctoral researcher from Taiwan’s Academia Sinica Institute of Astronomy and Astrophysics. The Mark 5B recorders are connected to the James Clerk Maxwell Telescope next door, which is contributing its 15-meter dish to tonight’s effort. “The Mark 5Cs”—the newest, highest-bandwidth recorders, and the ones hooked up to the Submillimeter Array—“are not.”

Doeleman, a slight man with a runner’s build, sprints out of the room and runs downstairs, where the recorders are installed. A few minutes later, he darts back into the control room, panting in the thin mountain air. He sits back down at his computer, pounds out a few keystrokes and mumbles something technical and reassuring to the postdocs and telescope operators. The recorders appear to be working.

A black hole should cast a shadow. The goal is to capture an image of that shadow.Three arrays is just a start. Doeleman and his cohort have been operating this same network of radio telescopes since 2007, when they pointed the array at the galactic center and detected “structure on the event-horizon scale,” a deeply obscured blip in space whose dimensions match the predicted size of Sagittarius A* (pronounced “A-star”), the four-million-solar-mass black hole at the center of the Milky Way. After that, with encouragement from colleagues, Doeleman decided that peering deeper into the galactic center, deep enough to actually take a picture of the very edge of Sagittarius A*, was not as implausible as it sounds. Detectors were becoming more sensitive every year; data storage and processing power had never been so cheap. If he could add the right telescopes to his network, taking a picture of Sagittarius A* should be, as Doeleman puts it, “eminently doable.”

Over the next few years, Doeleman says, he and his group will combine as many as a dozen of the world’s most sophisticated radio-astronomy installations to create “the biggest telescope in the history of humanity”—a virtual dish the size of Earth, with 2,000 times the resolution of the Hubble Space Telescope. Tonight the Event Horizon Telescope astronomers have a more limited goal: They want to catch as much light from Sagittarius A* as possible and study its polarization to learn about the black hole’s magnetic field. But eventually (if all goes well) astronomers using the fully scaled-up Event Horizon Telescope—a machine with resolution high enough to read the date on a quarter from 3,000 miles away—will see the silhouette of an object that is, in itself, unseeable.

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