From a distant galaxy, researchers capture evidence of a cosmic phenomenon that physics has only hinted at for decades.
As an idea, black holes have been with us for more than a century. By degrees they have been imagined, sensed, measured and even heard. Yet not until now have scientists been able to lay claim to the most direct form of proof to date.
For the first time, we know what a black hole looks like.
The jaw-dropping image – less impressive, perhaps, to non-experts for its appearance than for what it means – is as close as humanity has ever come to visualizing one of the dark behemoths churning away in distant corners of the universe.
“For me, seeing the thing makes it real in a way that knowing can’t,” said Avery Broderick, a researcher at the Perimeter Institute for Theoretical Physics and the University of Waterloo, and a long-time member of the team that produced the image.
Avery Broderick, a researcher at the Perimeter Institute for Theoretical Physics and the University of Waterloo, stands in front of the image of the black hole. Watch this video for Ivan Semeniuk’s explanation of the significance of the team’s discovery.
The “thing” Dr. Broderick and his colleagues revealed to the world on Wednesday is a behemoth – monstrous even by black-hole standards – buried in the heart of a distant galaxy called M87, more than 50 million light years away in the direction of the constellation Virgo.
The image was made by combining data from ground-based radio telescopes in eight locations. Its appearance is remarkably close to what theory had predicted.
Since black holes do not emit light, the image appears in silhouette, surrounded by a brilliant glow from the hot gas swirling around it. The distortion of space due to the black hole’s extreme gravity causes the glow to appear as a circular ring, as though viewed through a strong lens. The size and shape of the ring mathematically confirm that the black hole is larger than our solar system and contains the mass of more than six billion suns.
“I think that any scientist in any field would know what that feeling is to see something for the first time… to know that you’ve uncovered part of the universe that was off limits to us,” said Shep Doeleman, a Harvard University astronomer who initiated the project, known as the Event Horizon Telescope, more than a dozen years ago.
At a news briefing on Wednesday morning in Washington, Dr. Doeleman explained that no conventional camera or single instrument can produce such an image, which spans an area of the sky about the size of a Canadian two-dollar coin seen at the distance of the moon.
Instead, the sensitive radio dishes at facilities around the world map high-frequency radio signals emanating from the violent environment where superheated matter is on the brink of vanishing forever into the black hole.
The project began in 2007 with three locations – enough to test the idea but not enough to produce an image of a black hole. More observatories joined in, including the 66-dish ALMA array, based in Chile, and radio telescopes in Greenland and at the South Pole. This has significantly improved the sharpness and the level of detail the combined data can reveal.
The catch is that all stations need to have good weather to take their simultaneous measurements. Such an opportunity occurred in April, 2017. “We were very lucky,” said Daniel Marrone, a team member and astronomer at the University of Arizona. “Our first three days of observations were some of the best weather we’ve ever seen.”
Those data, after many months of analysis, yielded this week’s historic image.
“I have to admit I was a little stunned that it matched so closely the predictions that we had made,” Dr. Broderick said.
Those predictions are guided by the equations of Albert Einstein’s 1915 general theory of relativity, which describes gravity as curved space and demonstrates that when enough mass is concentrated in one place, the curve can become a trap. Whatever falls inside remains forever cut off from the rest of the universe behind a boundary known as the event horizon, which is not a physical barrier but a point of no return for light and everything else.
Even Einstein was skeptical such a thing could exist, but for decades, evidence has mounted that black holes are real. They are now known to come in two varieties. Some are formed by the gravitational collapse of massive stars. These are compact objects with event horizons measuring tens of kilometres across.
In contrast, the Event Horizon Telescope is aimed at supermassive black holes, which are thought to reside in the cores of most galaxies. Only two have the right combination of distance and size to yield an image. One is at the centre of our own Milky Way galaxy. Researchers with the project said they already have the data that could lead to an image of this object in the coming months.
The other target is the more remote but much larger black hole in M87.
Daryl Haggard, an astrophysicist at McGill University who is affiliated with the project, said the image links the action immediately around the black hole to regions just a bit further out, where electrically charged particles that have narrowly missed falling into the black hole are rocketed outward by powerful magnetic fields at nearly the speed of light.
“This is our first chance to really get in there, right down where material is at that decision point of falling in or being driven out,” she said.
Julie Hlavacek-Larrondo, a University of Montreal astrophysicist who is not a team member but whose work focuses on supermassive black holes, called the result an important counterpart to the recent detection of gravitational waves, minute vibrations produced by the collisions of stellar-size black holes.
“That gave us proof that small black holes exist. Supermassive black holes are an entirely different situation,” she said. “It’s still difficult for us to understand how the universe can create those kinds of monsters.”
The Globe and Mail, April 10, 2019