When the first-ever direct picture of a black hole was unveiled Wednesday, scientists around the world were almost giddy over finally getting a chance to see one of the most mysterious objects in the universe.
“A once-in-a-lifetime result,” exulted Shep Doeleman, director of the Event Horizon Telescope, the international team of scientists who created the image using a network of radio telescopes linked together to form a single, Earth-size observatory.
“I couldn’t imagine that I’d live to see a telescopic image of a black hole,” said Jean-Pierre Luminet of the French National Center for Scientific Research, who created the first visualization of a black hole in 1979. Yale astronomer Priya Natarajan was more succinct. “My first reaction on seeing the image was: Wow!”
The remarkable snapshot shows a monster black hole 55 million light-years from Earth in the neighboring galaxy M87. Nicknamed Pōwehi by some members of the team (it's pronounced poe-vay-hee, a word from Hawaiian mythology meaning “embellished dark source of unending creation”), the object is 6.5 billion times as massive as the sun and has a diameter of 24 billion miles. Its mass and powerful gravity cast a shadow against the bright, hot gas swirling around it, creating a distinctive donut shape.
The Event Horizon Telescope project is the culmination of a century of speculation about black holes, collapsed masses where gravity is so intense that no matter or even light can escape. Until now, scientists eager to understand these enigmas could study them only by indirect means: testing theories with computer simulations or watching how black holes’ intense gravitation affects matter and space around them. Now the objects are visibly, almost tangibly real.
Even more, the first picture of a black hole heralds a new era in physics. Now that they can observe these bizarre objects directly, experts say we can expect an avalanche of new observations — and new cosmic discoveries.
Einstein keeps acing the tests
One of the most striking things about the image of Pōwehi is how closely it resembles black hole simulations created with the help of computer models. Those models are all based on Einstein’s general theory of relativity, making the match an impressive vindication of the famous physicist’s ideas.
“We were surprised by how clear the signature was,” Doeleman told NBC News MACH in an email. “Einstein’s theory of gravity predicts that we should see a ring of light, but to have it come through so clearly rocked us back on our heels.” (A small irony: Einstein himself didn’t believe in black holes, arguing that while his equations indicated that such objects were theoretically possible, they “do not exist in physical reality.”)
The light ring around Pōwehi is distinctly lopsided, another predicted effect. Gas around the black hole is orbiting furiously, and the side that is circling toward Earth appears brighter than the side that is circling away. The pattern indicates that the black hole is rotating clockwise from our perspective, Heino Falcke, a radio astronomer at Radboud University in the Netherlands and a member of the Event Horizon Telescope team, said in an email.
The picture doesn’t reveal what happens at the event horizon, the theoretical “surface” of a black hole. The event horizon is one of the strangest predictions of Einstein’s relativity, the point of no return where time comes to a standstill. So far, the Event Horizon Telescope observations cannot confirm even the existence of an event horizon.
“It looks like an event horizon and it quacks like an event horizon, but you can never exclude something that is almost like an event horizon producing a similar shadow,” Falcke said. “Each competing model has to be tested one by one. The cool thing is — now we can.”
To warped space … and beyond
The astonishing power of the Event Horizon Telescope means that a lot of other outstanding questions in astronomy become suddenly answerable, too.
“It gives us, for the first time, a way to test our predictions for how black holes digest matter and launch powerful jets of material that can disrupt entire galaxies,” Doeleman said. Such jets can grow 100,000,000 times as wide as the black hole itself, and nobody knows exactly how they form.
The regions around black holes are also extreme places where gas is heated to millions of degrees and whipped around at nearly the speed of light. They are natural laboratories for testing the outer limits of the laws of physics. “The next step is to sharpen the image further so we can study the dynamics of the black hole — how does it change, how does it affect its surroundings. This will let us go from making still images of black holes to making movies,” Doeleman said.
Pōwehi is just one of billions of supermassive black holes now thought to exist across the universe, in the centers of most large galaxies. Future upgrades to the Event Horizon Telescope will bring more of these objects into view, including Sagittarius A* (pronounced Sagittarius A star), the huge black hole at the center of our own Milky Way galaxy. Falcke and the rest of the team have already made attempts to see Sagittarius A*, but our local black hole flickers rapidly, making it what he termed “an extra challenge."
The Event Horizon Telescope will be a godsend for many other kinds of astronomical observations beyond black holes.
“The resolving power of the telescope is just astonishing,” Mustafa Amin and Andrea Isella, astronomers at Rice University, said in an email. (Its acuity is equivalent to reading the emails off an iPhone in New York City while lounging in a café in Paris.) They are eager to exploit that power to watch infant planets forming around other stars or to observe delicate structures in distant galaxies.
The possibilities are almost endless. First, though, Falcke and the other black hole sleuths are looking forward to some well-earned sleep. “People were worn out to get this massive amount of work done under this pressure,” he said. “It would be really good to pause for a moment and rethink the way we do things.”
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