This image from the Event Horizon Telescope shows the supermassive black hole in the elliptical galaxy M87, surrounded by superheated material. (EHT Collaboration)
WASHINGTON — Scientists 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 known as the Event Horizon Telescope delivered a fuzzy view of the dark monster at the center of an elliptical galaxy known as M87 today during a global wave of briefings.
“This is a remarkable achievement. … It’s almost humbling in a certain way,” Shep Doeleman, the project’s director, said during a news briefing here at the National Press Club..
The National Science Foundation provided streaming-video coverage of the big reveal. Scientists in Europe and Japan streamed separate briefings in Brussels and Tokyo. Still more news conferences were happening in Chile, China and Taiwan.
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 what would otherwise be an invisible black hole.
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 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 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 showing the radio signature of M87’s black hole, 6.5 billion times more massive than our sun, was released at today’s briefings. Sera Markoff, an astrophysicist at the University of Amsterdam who is a member of the EHT Science Council, said M87’s black hole was easier to spot than our own galaxy’s black hole because it’s in more of an active state.
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. In an email, Agol also noted that a colleague of his at UW, Bruce Balick, was in on the discovery of Sagittarius A* 45 years ago.
“I am not involved in the EHT, so I haven’t seen any of the results, but I am excited to see them!” Agol said.
Based on computer simulations, the event horizon of M87’s black hole — that is, the boundary within which light waves can’t escape — looked like a circle of black, surrounded by bright streams of superheated material swirling around the shadow. But the picture wasn’t nowhere near 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. This first image of a supermassive black hole almost certainly will be improved upon in years to come.