WASHINGTON, D.C. — Scientists today shared the first picture to show the immediate surroundings of a galaxy’s supermassive black hole, captured by a network of radio telescopes that adds up to what could be considered the world’s widest observatory.
A project called the Event Horizon Telescope delivered a fuzzy view of the dark monster at the center of an elliptical galaxy known as M87. The edge of the black hole’s dark circle, known as the event horizon, was surrounded by the bright glare of superheated material falling into the black hole.
“This is a remarkable achievement. … It’s almost humbling in a certain way,” EHT project director Shep Doeleman, an astronomer at the Harvard-Smithsonian Center for Astrophysics, said during a news briefing here at the National Press Club.
Even France Cordova, director of the National Science Foundation, was impressed.
“This is the first time that I saw this image right now … and it did bring tears to my eyes,” she said. “So this is a very big deal.”
NSF provided streaming-video coverage of today’s big reveal. Scientists in Europe and Japan streamed separate briefings in Brussels and Tokyo. Still more news conferences took place in Chile, China and Taiwan. The details were laid out in six papers published in a special issue of The Astrophysical Journal Letters.
The Event Horizon Telescope, or EHT, is actually an consortium of radio telescope facilities that are combining efforts to do what none of them could do on their own: chart the bright halo of hot material that surrounds a black hole’s event horizon.
““We have seen what we thought was unseeable,” Doeleman said.
As any science-fiction fan knows, black holes are concentrated areas of gravitational collapse so massive that nothing — not even light — can escape their pull.
If a dying star is massive enough, on the order of 10 or 20 times as massive as our sun, it’s likely to collapse into a black hole when it dies. But the biggest black holes are the ones that form at the center of galaxies as they evolve. These supermassive monsters can weigh millions or even billions of times as much as our sun
Our own Milky Way galaxy has just such a black hole at its core. Fortunately, our galaxy’s supermassive black hole is on the quiet side.
In April 2017, eight radio telescope facilities that are participating in the Event Horizon Telescope project took a close look at our galaxy’s central region, known as Sagittarius A* (that is, Sagittarius A-star, abbreviated as Sgr A*). The team also tried capturing an image of the supermassive black hole at the center of M87, about 55 million light-years from Earth.
The EHT facilities were in Arizona, Hawaii, Mexico, Chile, Spain and even the South Pole. Results from any one of the telescopes wouldn’t have anywhere near the resolution to make out the hot surroundings of the black hole.
To bring the picture into focus, the Event Horizon Telescope’s teammates had to combine their observations using a technique known as very long baseline interferometry, or VLBI. The technique for synchronizing observations effectively turns their network into a huge radio telescope almost as wide as our planet.
The image released today shows the radio signature of M87’s black hole, which is about 23.6 billion miles wide — more than four times as wide as the orbit of Neptune — and 6.5 billion times more massive than our sun. As big as it is, spotting the black hole from tens of billions of light-years away was a challenge.
“It’s the equivalent of being able to read the date on a quarter in Los Angeles when we’re standing right here in D.C.,” Doeleman said.
Based on the pattern of light surrounding the black hole, scientists could even figure out that it’s spinning clockwise.
M87’s black hole was easier to spot than our own galaxy’s black hole because it’s in more of an active state. But if it were too active, the superheated gas surrounding the black hole would have been too bright to see the event horizon’s dark circle.
“We just got lucky,” said Sera Markoff, an astrophysicist at the University of Amsterdam who is a member of the EHT Science Council.
Doeleman said the team was still working to produce an image of Sagittarius A*, but the task is more complex than it is for M87.
Avery Broderick, a theoretical physicist at Canada’s Perimeter Institute and the University of Waterloo, noted that the circular shape of the event horizon was totally consistent with Albert Einstein’s theory of general relativity.
“Today, general relativity has passed another crucial test, this one spanning from horizons to the stars,” he said.
University of Washington astronomer Eric Agol played a key role in suggesting VLBI as a way to view the “shadows” of supermassive black holes back in 1999.
“It’s taken a lot longer than we expected, but it’s a really amazing technical accomplishment,” Agol, who isn’t on the EHT team, told GeekWire by telephone after seeing the picture for the first time. “And the image is pretty amazing as well.”
White House science adviser Kelvin Droegemeier said he ranked the Event Horizon Telescope’s image right up there with the Nobel-winning first detection of gravitational waves by the Laser Interferometer Gravitational-wave Observatory, or LIGO. Even people who may not understand the physics of black holes “know it’s really, really cool,” Droegemeier told GeekWire.
“These are just singular moments in history,” he said. “We as humans need this.”
The picture of M87’s black hole wasn’t nearly as sharp as the depictions of black holes you’ve seen in movies such as “Interstellar.” With a limited number of participating telescopes, even VLBI can take you only so far.
Fortunately, more telescopes have joined the campaign over the past couple of years, and astronomers are working on ways to improve their data processing methods at different wavelengths. “We also want to go into space,” Doeleman said, by launching an observatory that could be added to the Event Horizon Telescope.
All of which means that this first image of a supermassive black hole almost certainly will be improved upon in years to come.
Here are the six open-access papers authored by the Event Horizon Telescope collaboration and published by The Astrophysical Journal Letters, with “First M87 Event Horizon Telescope Results” as the overall title:
- “I. The Shadow of the Supermassive Black Hole”
- “II. Array and Instrumentation”
- “III. Data Processing and Calibration”
- “IV. Imaging the Central Supermassive Black Hole”
- “V. Physical Origin of the Asymmetric Ring”
- “VI. The Shadow and Mass of the Central Black Hole”
This report has gone through frequent updates, most recently at 10:57 a.m. PT.
