It’s Albert Einstein’s weirdest prediction — that the universe is sprinkled with massive objects so dense that not even light can escape them. Although Einstein was skeptical the theory was true, it has held for over a century. Today, astronomers are fairly convinced that nearly every galaxy (including our own) harbors a black hole so massive that it gobbles down any nearby gas and dust, often ripping stars to shreds. And while no one has seen a black hole directly, astronomers might finally be on the brink of doing just that.
For the next 10 days, eight radio observatories at six locations across the globe will be pointed toward the supermassive black hole that hides in the Milky Way’s center. Should the weather cooperate at these observatories — which span the peak of the world’s tallest volcano in Hawaii, the frigid landscape at the South Pole, and the ski-covered slopes of the Sierra Nevada in Spain — astronomers will collect data at a scale never attempted before in physics.
The hope is to image the black hole’s event horizon, the gravitational point of no return, for the first time. Although it’s but a tiny shadow against a glowing backdrop of radiation in the center of the Milky Way galaxy, the image would provide further evidence that black holes exist, put Einstein’s general theory of relativity to one of its most stringent tests, and ultimately help astronomers understand how black holes rule over their respective galaxies.
“We hope to see the un-seeable,” says Shepard Doeleman, director of this Event Horizon Telescope (EHT). “We want to see something that by its very nature tries to do everything it can not to be seen. It’s the ultimate cloaking device.”
Seeing the Unseen
Although astronomers have known since the 1970s that a supermassive black hole, called Sagittarius A*, lurks in the center of the Milky Way, imaging the black hole seemed impossible. That’s because while Sagittarius A* is quite heavy, at a mass of 4 million times that of the sun, it’s also puny, with a radius that’s just 17 times wider. To see something so small from 26,000 light-years away requires a radio dish of global dimensions.
That might sound out of the question, but it isn’t with interferometry — a technique that integrates multiple observatories into one virtual telescope with a size as big as the distance between the locations. Dimitrios Psaltis, EHT’s project director, likes to explain it like this: If one pokes holes in a single mirror in a telescope, that telescope will still create the same image as before — just fainter. So an interferometer is simply a telescope with holes. Or in the case of the EHT, it’s a telescope composed of mostly holes with a few disparate mirrors.
For more than a decade, astronomers have been slowly adding observatories to the Earth-sized telescope, helping it grow to a worldwide collaboration involving 30 institutions in 12 countries. This year, astronomers will add the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and the South Pole Telescope in Antarctica — two crucial sites that will sharpen the virtual telescope’s resolution so much that it’s 1,000 times stronger than the Hubble Space Telescope. “We could watch a hockey game on the moon because we could resolve the puck,” says Avery Broderick, a theorist at the Perimeter Institute for Theoretical Physics. And that should make all the difference.
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SOURCE: NBC News, Shannon Hall