After months of investigating, they found out what was wrong, uncovering a defect in a radio receiver in Hawaii. “A lot of science,” says Doeleman, “is picking yourself up and dusting yourself off and trying again.” That’s exactly what they did in 2007, using the same telescopes in Arizona and Hawaii, with a third telescope from California thrown in to round out the initial trio of EHT stalwarts.
Reviewing the data the second time around, Doeleman started to get “a tingly feeling.” He realized that the radio emissions from Sagittarius A* — emanating from the white-hot material swirling around the black hole like water circling a bathtub drain — were coming from a region that was significantly smaller than expected. For practical reasons this was extremely fortuitous, as most astronomers had assumed the black hole would be too big to get a good look at, he explains, “like putting your face right next to the wall and trying to describe it.”
Doeleman and his cohorts not only saw the wall; they came away with some of the highest-resolution observations ever achieved in astronomy. It was comparable to spotting a baseball on the surface of the moon. This was the first successful test of the EHT concept, says Doeleman, “the ‘aha!’ moment when we knew we were really onto something. We knew that we finally had access to a region of space-time” — just outside the black hole’s event horizon —“that had, until now, eluded astronomers.”
But the true objective of the EHT is yet to come. So far, Doeleman and company have only been able to establish that radio emissions near a black hole originate from a specific region whose size they can determine. They cannot, however, make a detailed map or picture of it. That’s the next stage — acquiring bona fide snapshots of a black hole and its environs — and it will take an expanded EHT network, with a broader global reach, to achieve it. Obtaining such images, Doeleman says, “will give us a much greater ability to tease out details. We’ll get to see in an unbiased way exactly what’s up there.”
The Big Picture Gets Bigger
In addition to witnessing the galactic light show as the G2 cloud falls into Sagittarius A*, the EHT could address more fundamental questions about our universe. More specifically, the researchers would like to capture the silhouette of a black hole — a bright ring of hot, luminous gas surrounding the dark, unrevealing interior of the black hole itself.
This glowing ring, called the last photon orbit, represents the innermost place that light can orbit a black hole without irrevocably falling in. It is just outside the event horizon. The ring’s shape, moreover, provides a testing ground for general relativity (Albert Einstein’s theory of gravity), which predicts a mostly circular shadow. “If we see a weird shape that deviates significantly from a circle, we can try to figure out what kind of deviation from general relativity is required to produce it,” says Avery Broderick, a theoretical astrophysicist at Waterloo University and the Perimeter Institute. To see the shadow, Broderick adds, you need an instrument as powerful as the EHT. “That’s the only thing around that can do it.”
Einstein unveiled his theory in 1915, and it has withstood every test experimentalists have thrown at it, so finding any departures from general relativity would be huge. Producing an image that puts this century-old theory of general relativity on trial won’t require any conceptual breakthroughs, says Doeleman. “It’s just a matter of putting more telescopes around the Earth” — installing more “light buckets” that can collect more photons and thereby amass more information while simultaneously boosting the angular resolution. He’s working on it.
The team’s near-term goal is to expand the EHT from its three present sites to nine or 10, including telescopes in Antarctica, Greenland, Mexico and the recently upgraded one at Haystack — “the dish that got me started,” as Doeleman notes. The biggest contribution to the system, by far, will come from the Atacama Large Millimeter Array (ALMA) in Chile, the largest radio telescope of its kind. That’s why Doeleman and his EHT colleagues are hard at work devising a way to extract radio signals from 50 or more radio dishes at ALMA without interfering with the array’s primary mission: studying the origins of the universe.
Going to a billion-dollar radio facility like ALMA, more than 16,000 feet above sea level, and getting it to mesh with the rest of their network is the kind of technological problem Doeleman relishes. Every component has to be double- and triple-checked, he says, to make sure the system as a whole can perform interferometry of the highest precision. “But for me, making a new telescope work in this way is really a rush.”
Of course, the project involves more than just feats of technical wizardry. Ultimately, it’s about capturing a glimpse of some of the most bizarre places in the universe — places we previously could only speculate about, he says. It’s about getting as close to a black hole as our technology will take us, pulling back from the edge and sharing the extraordinary view with the world.