Astronomers needed an Earth-sized telescope to photograph the gigantic black hole at the center of the Milky Way, and the next time they take on ongoing observations, NASA’s Next-Generation Space Observatory will help.
James Webb Space Telescope, also known as JWST or Webb, was launched in December 2021 and is completing preparations for observing the Universe. Among the tasks planned for the first year of operation of the new observatory is the unification Event horizon telescope (EHT), a global array of observatories that released the world’s first photograph of a black hole in April 2019.
EHT repeated the feat in May when it published the first image Sagittarius A*supermassive black hole at the center of our Milky Way galaxy, in May, revealing lumpy, blurry, golden ring on a black background.
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One of the countless scientists waiting to see this image was Farhad Yousef-Zadeh, an astronomer at Northwestern University in Illinois. He was particularly interested in the EHT work on Sagittarius A* because earlier this year he was given precious time at the JWST to observe the giant black hole.
The picture did not disappoint. “It was a nice surprise,” he told Space.com.
“I thought the image would be a little more erratic due to the volatility of Sagittarius A*,” he said. “Of course, it looks good – for the first image.”
Sagittarius A* is a difficult subject to study because – in addition to all the usual restrictions black hole Spots along its event horizon suddenly eject particles at almost the speed of light. (A black hole’s event horizon is a point beyond which nothing, not even light, can escape.) These flares can occur four or five times a day, making Sagittarius A* a particularly volatile beast.
“These hotspots basically suddenly turn on and flare up,” Yousef-Zadeh said. “Basically, it’s like fireworks, and it lasts for about half an hour or so. Sometimes they get together; you have several fireworks, at the same time or one after the other.”
But the mechanics of the flashes themselves remains a mystery.
“We still don’t know how missiles are made,” Yousef-Zadeh said. “Flashes are particles like cosmic rays that move close to speed of light. Something must have really accelerated them to approach the speed of light, and we still don’t know what it is.”
Each flash is initially visible in infrared light, but over time the signal transitions into what astronomers call submillimeter radiation. And coincidentally, this is the submillimeter radiation that the Event Horizon Telescope collects to take its images of a black hole, which means that EHT scientists are detecting a signal from an underlying black hole and a signal from a flare.
“This is the worst thing that can happen to a black hole image because you don’t want to observe a variable source,” Yousef-Zadeh said. “You need to remove the variable component to really create a proper image of the source itself.”
This is where Webb comes in.
JWST brings several benefits to collaboration. The orbit of a point nearly 1 million miles (1.5 million kilometers) from Earth, no cloudy weather interfering with observations. The distant vantage point, along with the observatory’s massive sunshade, keeps its instruments cool enough to study infrared light. What’s more, Webb boasts two instruments that can simultaneously collect data in two different types of infrared light.
“As far as I know, the ability to simultaneously observe near- and mid-infrared flares has never been seen before,” Yousef-Zadeh said. Continuous observations at both wavelengths should allow scientists to distinguish between Sagittarius A* and its flares. “Basically, it’s like two telescopes observing at the same time.”
(venerable NASA Hubble Space Telescope studied Sagittarius A* in the infrared. But Hubble can only track one wavelength at a time, and it observes in chunks of just 45 minutes as it passes between day and night in Earth’s orbit.)
Due to the partnership with the EHT, the Yousef-Zadeh team is subject to program scheduling restrictions, which typically make observations during a week in March or April to determine the most promising weather. The campaign next spring is tentatively scheduled for April 2023, he said, when JWST spends 25 hours studying the supermassive black hole.
Regardless of the EHT observations, Yousef-Zadeh said he expects Webb’s observations of flares to teach scientists a lot about how these features work.
But will Sagittarius A* flash while Webb watches him? Yousef-Zade believes that the odds are in favor of his team. “I have a feeling that two days is good, and if that doesn’t work, you will be back next year,” he said. “We’ll try again, this is not a one-time deal.”
And even if JWST fails to catch the flash, the observations will still be valuable, he stressed, given the partnership with the Event Horizon Telescope. “Some people might really like the lack of glare – meaning the image is pretty good, then it won’t interfere with the EHT image at all,” he said.
Ultimately, he said, he would accept whatever observations he received. “This is a black hole. She can do whatever she wants.”
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