Astronomers needed an Earth-sized telescope to image the monster black hole at the center of the Milky Way – and the next time they tackle continued observations, they’ll have help from the observatory next generation spacecraft from NASA.
The James Webb Space Telescope, also known as JWST or Webb, launched in December 2021 and is completing preparations to begin observing the universe. Among the tasks planned for the first year of work of the new observatory, is the association with the Event Horizon Telescope (EHT), the global network of observatories that released the first-ever photo of a black hole in April 2019.
The EHT repeated the feat in May, when it released the first image of Sagittarius A*the supermassive black hole at the center of our Milky Way galaxy, in May, revealing a lumpy, fuzzy, golden ring on black background.
Live updates: NASA’s James Webb Space Telescope Mission
Related: How the James Webb Space Telescope works in pictures
One of the countless scientists waiting to see this image was Farhad Yusef-Zadeh, an astronomer at Northwestern University in Illinois. He has been particularly invested in the EHT’s work on Sagittarius A* because earlier this year he was granted valuable time on JWST to observe the monster black hole.
The photo did not disappoint. “It was a nice surprise,” he told Space.com.
“I thought the picture would be a bit more messy due to the variability of Sagittarius A*,” he said. “Looks pretty good, that’s for sure – for a first image.”
Sagittarius A* is a delicate object to study because — in addition to all the usual constraints of a black hole – specks along its event horizon suddenly shoot out particles at near the speed of light. (The event horizon of a black hole is the point beyond which nothing, not even light, can escape.) These flares can occur four or five times a day, making Sagittarius A* a particularly changeable beast.
“These hotspots suddenly ignite and flare up,” Yusef-Zadeh said. “It’s like a fireworks display, basically, and it lasts about half an hour. Sometimes they come together, you have multiple fireworks, simultaneously or one after the other.”
But the mechanics of the flares themselves are a mystery.
“We still don’t know how flares are produced,” Yusef-Zadeh said. “Flashes are particles like cosmic ray particles that move near the speed of light. Something must have really accelerated them to near the speed of light, and we still don’t know what it is.”
Each flare is first visible in infrared light, but over time the signal expands into what astronomers call sub-millimeter radiation. And coincidentally, it’s the sub-millimeter radiation that the Event Horizon Telescope gathers to create its black hole images – meaning that EHT scientists detect the signal from the underlying black hole and that from the flare.
“That’s the worst thing that can happen to imaging a black hole, because you don’t want to observe a variable source,” Yusef-Zadeh said. “You have to remove the variable component to really build a proper image of the source itself.”
This is where Webb comes in.
JWST brings several assets to the collaboration. Orbiting a point nearly 1 million miles (1.5 million kilometers) from Earth, there is no cloudy weather to interfere with the observations. And the distant vantage point, along with the observatory’s huge sunshade, keeps its instruments cool enough to study infrared light. Additionally, Webb has two instruments capable of simultaneously collecting data in two different types of infrared light.
“As far as I know, having the ability to simultaneously observe near-infrared and mid-infrared flaring events has never been done before,” Yusef-Zadeh said. Continuous observations at both wavelengths should allow scientists to distinguish between Sagittarius A* and its flares. “It’s like two telescopes, basically, observing simultaneously.”
(venerable NASA The Hubble Space Telescope studied Sagittarius A* in infrared. But Hubble can only monitor one wavelength at a time, and it observes in only 45-minute increments as it passes between day and night in Earth orbit.)
Because of the partnership with the EHT, Yusef-Zadeh’s team is subject to the scheduling constraints of the program, which typically conducts its observations over about a week in March or April to aim for the most promising weather. Next spring’s campaign is tentatively scheduled for April 2023, he said, when the JWST will spend 25 hours studying the supermassive black hole.
Regardless of the EHT observations, Yusef-Zadeh said he expects the Webb observations of the eruptions to shed some light on how these features work for scientists.
But will Sagittarius A* go up in flames while Webb watches? Yusef-Zadeh thinks the odds favor his team. “I feel like having two days is fine, and if it doesn’t work out, you come back the following year,” he said. “We will try again, this is not a one-off deal.”
And even if JWST can’t catch a flare, the observations will still be valuable, he pointed out, given the partnership with the Event Horizon Telescope. “Some people may really like that there are no flares – that means the imaging is going to be pretty good, so it doesn’t interfere with the EHT imaging at all,” he said .
Ultimately, he said, he’ll take whatever observations he gets. “It’s a black hole. It can do whatever it wants.”