The Webb Telescope Has Observed the Black Hole at the Center of the Milky Way and Discovered a Chaotic Light Show

Astronomers first observed the supermassive black hole at the center of the Milky Way galaxy in 2022. The James Webb Space Telescope recently provided them with a new opportunity to study its surroundings, revealing a chaotic light show that never ends.

Context. At the heart of the Milky Way galaxy lies a gigantic black hole known as Sagittarius A* (Sgr A*). Astronomers have made significant progress in understanding the extreme dynamics of its accretion disk, the spiral of gas and dust that orbits the black hole. To achieve this, they observed Sgr A* for 48 hours, divided over several sessions in 2023 and 2024, using the NIRCam instrument on the Webb telescope.

A disco ball. The observations have shown that Sgr A* emits a continuous array of light and dynamic flashes, characterized by a constant flicker interspersed with intense bursts of brightness.

These emissions consist of a faint, steady component likely arising from internal turbulence within the disk and bright, short-lived flares linked to magnetic reconnection. This phenomenon occurs when magnetic fields collide, releasing vast amounts of energy. The fluctuations in brightness can happen within seconds or extend over days, weeks, and even months.

Why it happens. The study, published in The Astrophysical Journal Letters, explores variable emissions and suggests that these fluctuations become more intense on larger scales. According to researchers, small internal disturbances within the accretion disk, which are linked to changes in density and magnetic fields, generate faint flares. In contrast, larger eruptions are associated with point-like magnetic reconnection events, similar to solar flares, but occurring at much higher energy levels.

“In our data, we saw constantly changing, bubbling brightness. And then boom! A big burst of brightness suddenly popped up. Then, it calmed down again. We couldn’t find a pattern in this activity,” study author Farhad Yusef-Zadeh explained. This seemingly random behavior indicates that the accretion disk is continuously regenerating, producing five to six large eruptions each day, along with multiple intermittent bursts.

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A surprising discovery. One advantage of the Webb telescope’s NIRCam instrument is its ability to observe two infrared wavelengths simultaneously (2.1 and 4.8 microns). This capability allowed researchers to compare how the brightness of flares changed at each wavelength.

Surprisingly, they discovered that events observed at the shorter wavelength changed brightness slightly earlier than those at the longer wavelength. “This is the first time we have seen a time delay in measurements at these wavelengths. “[We] noticed the longer wavelength lags behind the shorter one by a very small amount–maybe a few seconds to 40 seconds,” Yusef-Zadeh said.

This finding provides crucial insight into the process of synchrotron cooling, where energetic particles lose energy as they cool.

Next observations. Researchers now plan to use the Webb telescope to observe Sgr A* continuously for up to 24 hours. This will help them determine whether the bursts of brightness follow repetitive patterns or are truly random.

Every flash and flicker in the accretion disk of the supermassive black hole enhances the scientific community’s understanding of the physics at the event horizon. It’s one of the most extreme environments in the universe. In other words, it helps scientists explore how space, time, and matter behave under the influence of immense gravity.

Images | Aman Pal | NASA/ESA/CSA/Ralf Crawford (STScl)

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