20-02-2025
Webb Catches Mysterious Light Flares Around Milky Way's Supermassive Black Hole
Between spotting galaxies that shouldn't exist, capturing the interstellar medium with unprecedented clarity, and identifying new worlds, the James Webb Space Telescope is a busy observatory. But as it orbits the Sun, Webb has kept a close eye on one of the most obscure pieces of our galaxy: Sagittarius A*, the supermassive black hole at the center of the Milky Way. By capturing the longest and most detailed Sag A* observations yet, Webb has allowed astronomers to catch a constant light show around the black hole's accretion disk, which draws in Sag A*'s cosmic meals.
In a study published Tuesday in The Astrophysical Journal Letters, an international team of researchers from several space science organizations shared that Webb's NIRCam (Near-InfraRed Camera) spotted many pops of light near Sag A* across 48 hours of observation. These flashes, which varied in strength, appeared to flare from the inner edge of the black hole's accretion disk.
Flares aren't unusual near supermassive black holes, so on its own, the identification of light flares around Sag A* wouldn't have been particularly exciting. What was odd about the team's findings was that Sag A*'s light show never appeared to stop, even as the team studied the flashes over seven 8-to-10-hour observation periods between 2023 and 2024. The only variables they noticed were in wavelength and length of time—data that, thanks to NIRCam's dual modules, could be captured simultaneously during a single session.
"Flares are expected to happen in essentially all supermassive black holes, but our black hole is unique," said astrophysicist and lead study author Farhad Yusef-Zadeh in a Northwestern University statement. "It is always bubbling with activity and never seems to reach a steady state. We observed the black hole multiple times…and we noticed changes in every observation. We saw something different each time, which is really remarkable. Nothing ever stayed the same."
Yusef-Zadeh and his colleagues believe the flares could be the product of the same phenomenon that produces sporadic flashes near other black holes: feisty accretion disks. These swirling disks of gas and dust gravitationally pull matter toward the black hole, eventually tipping that material past the point of no return (the black hole's event horizon). This steady stream of snacks allows the black hole to grow in mass. Every now and then, turbulence within the accretion disk squeezes the disk's plasma, triggering a quick burst of radiation.
"It's similar to how the Sun's magnetic field gathers, compresses, and then erupts a solar flare," Yusef-Zadeh told NASA. "Of course, the processes are more dramatic because the environment around a black hole is much more energetic and much more extreme. But the Sun's surface also bubbles with activity."
But an even more powerful force could be behind Sag A*'s larger flares. When two magnetic fields collide in space, they release energy in the form of accelerated particles. These particles travel so fast that they emit bright bursts of radiation, according to NASA. If "magnetic reconnection events" are happening in Sag A*'s accretion disk, that could explain the more aggressive pops of light.
In the future, the researchers hope to use Webb's NIRCam to observe Sag A* for 24 hours straight. Only a long, uninterrupted period like this would allow the team to see whether the accretion disk's light show is based on any particular pattern or is truly random.
