NASA's Webb telescope captures flare from black hole at the center of the Milky Way

Northwestern University astrophysicists used NASA's James Webb Space Telescope to conduct the longest and most detailed observations yet of the supermassive black hole at the center of the Milky Way. They found that the black hole's accretion disk was constantly emitting flares without a break. This video shows 2.1 micron data taken on April 7, 2024. Source: FarhadYusef-Zadeh/Northwestern University

The findings could provide crucial insights into the nature of black holes, their interactions with their surroundings, and the forces that influence the evolution of the Milky Way. The research will be published today (February 18) in The Astrophysical Journal Letters.

Farhad Yusef-Zadeh of Northwestern University, who led the study, said: "Flares are expected to occur in essentially all supermassive black holes, but ours is unique. It is continuously active and never seems to be. Achieving a stable state. We observed this black hole multiple times during 2023 and 2024, and every time we observed it, we saw something different, which is really remarkable."

Yusef-Zadeh is an expert on the galactic center and a professor of physics and astronomy in Northwestern University's Weinberg College of Arts and Sciences. Co-authors on the international team include Howard Bushouse of the Space Telescope Science Institute, Richard G. Arendt of NASA, Mark Wardle of Macquarie University in Australia, Joseph Michail of Harvard University and Smithsonian College, and Claire Chandler of the National Radio Astronomy Observatory.

To conduct the study, Yusef-Zadeh and his team used JWST's Near Infrared Camera (NIRCam), which can observe two infrared colors simultaneously for long periods of time. Using this imaging tool, the researchers observed Sagittarius A* for up to 48 hours - measured in 8- to 10-hour increments, spanning a year. This allows scientists to track how the black hole changes over time.

Although Yosef-Zadeh expected to see a flare, Sagittarius A* was more active than he expected. Simply put: Observations show that fireworks vary in brightness and duration. The accretion disk around the black hole produces five to six large flares per day, interspersed with several smaller secondary flares.

Although astrophysicists don't fully understand the process, Yusef-Zadeh suspects that the short bursts and longer flares are caused by two different processes. If the accretion disk were a river, then the short, weak flashes would be like small, random ripples on the river's surface. Longer, brighter flares, on the other hand, are more like tides and are caused by more significant events. Small perturbations within the accretion disk may produce faint flickers. Specifically, turbulent fluctuations within the accretion disk compress plasma, a hot, electrically charged gas, causing brief bursts of radiation. Yosef-Zadeh compared the phenomenon to a solar flare.

He explained: "This is similar to the process of the sun's magnetic field gathering, compressing and then erupting in a solar flare. Of course, this process is more violent because the environment around the black hole is higher energy and more extreme. However, the sun's surface is also very active."

Yusef-Zadeh attributes the large, bright flares to magnetic reconnection events - the process in which two magnetic fields collide, releasing energy in the form of accelerated particles. These particles fly at nearly the speed of light, sending out dazzling pulses of radiation. Magnetic reconnection events are like electrostatic sparks. In a sense, this is also an 'electrical reconnection'.

Because JWST's NIRCam can simultaneously observe two different wavelengths (2.1 and 4.8 microns), Yusef-Zadeh and his collaborators were able to compare how the flare's brightness changes with each wavelength. Capturing two wavelengths of light is like "seeing in color instead of black and white," Yousef-Zadeh said. By observing Sagittarius A* at multiple wavelengths, he captured a more complete and nuanced picture of its behavior.

However, the researchers were in for another surprise. They unexpectedly found that events observed at shorter wavelengths changed in brightness slightly earlier than events observed at longer wavelengths.

"This is the first time we've seen a time delay in measurements at these wavelengths," said Yusef-Zadeh. "We observed these wavelengths simultaneously with NIRCam and noticed that the longer wavelengths lagged behind the shorter wavelengths by a small amount - perhaps a few seconds to 40 seconds."

This time delay provides additional clues to the physical processes occurring around the black hole. One explanation is that particles lose energy during the flare - particles with shorter wavelengths lose energy faster than particles with longer wavelengths. This change is expected for particles orbiting magnetic field lines.

To further explore these questions, Yusef-Zadeh hopes to use JWST to conduct longer observations of Sagittarius A*. He recently submitted a proposal to conduct 24-hour observations of the black hole. Longer observations will help reduce noise, allowing researchers to see finer details.

"You have to compete with noise when observing such weak flare events," said Yusef-Zadeh. "If we can observe for 24 hours, then we can reduce the noise and see features that we couldn't see before. We can also see whether these flares appear to be periodic (or recurring), or whether they are truly random."