It’s time for a black hole to shine.
A dozing monster of a black hole lies at the heart of our galaxy, and a global group of astronomers wants to snap its picture.
They expect to see a ring of hot plasma swirling around a blank spot, the death dance of gas clouds getting sucked into a sphere of no return, the so-called event horizon.
“The thing we will actually see is light just barely escaping from the black hole,” said Dan Marrone, a University of Arizona astronomer involved in the new project, called the Event Horizon Telescope.
Astronomers call black holes the most baffling objects in the universe. The powerful gravity of these collapsed stars sucks in everything around them.
And no one has ever taken a picture of one.
The reason: No single telescope is powerful enough to spy one. The black hole at the center of the Milky Way is as wee in the sky as a baseball on the moon. To see it, astronomers will synchronize a network of telescopes into an Earth-size super-telescope.
Once the network is assembled, dozens of radio dishes from California to the South Pole will simultaneously peer at the Milky Way’s center, each recording a bit of whatever’s there. Computer disks from each station will then be flown to Massachusetts, where a supercomputer at MIT’s Haystack Observatory will collate the data and build an image.
This picture won’t reveal the core of the black hole, as nothing — not even light — can escape it. But the picture should reveal never-before-seen details of the action swirling around it.
The image will also test Einstein’s theory of gravity. Called general relativity, the theory, published in 1916, has withstood every challenge thrown its way. It perfectly predicts how gravity bends light around stars, for instance.
But near the black hole, which astronomers call Sagittarius A* (pronounced “Sagittarius A-star”), gravity grows enormous. That’s because the object is as massive as nearly 4 million suns. (In astrophysical parlance, it’s “supermassive.”) As a result, the predictions made by general relativity might break down.
If Einstein was correct, the ring of gas around the black hole should appear almost perfectly circular. But if he was wrong, the ring might be squished.
The image might help solve another mystery: why Sagittarius A* is such a skimpy eater. It nibbles gas even though astronomers would expect it to be scarfing. “It’s basically gone to sleep,” said Chris Reynolds, who studies black holes at the University of Maryland at College Park.
Astronomers had long suspected that there was a black hole in the center of the galaxy, but it took until 2008 for two teams to confirm it. That’s when they “weighed” the black hole by clocking stars accelerating around it like boats swirling down a whirlpool. Measuring this acceleration allowed them to calculate the mass of the object in the middle. And only one thing in the universe can be as massive as 4 million suns: a black hole.
Astronomers on the project met last week in Tucson to finalize plans. They have already linked three radio telescopes, in California, Arizona and Hawaii, to obtain a fuzzy image of the black hole region. By 2014, when 66 radio dishes are in place in the high Chilean desert, the globe-spanning super-scope will be complete and able to provide a much sharper picture.
But even if the project succeeds, a central mystery will remain: What, exactly, is a black hole?
Einstein’s theory predicts a “singularity” in the middle, a point where gravity zooms to infinity and time stands still. No one really understands what that means; and because no light can emerge from a black hole’s event horizon, no telescope will ever be able to see its core.
“It’s amazing we have objects so bizarre and so extreme,” said Reynolds. “But they’re really there. Nature has really made them. You can talk about magic as much as you want – but these exist.”