Milky Way’s central black hole is generating massive bursts of energy

At the center of the Milky Way, a supermassive black hole called Sagittarius A* is never at rest. Using NASA’s James Webb Space Telescope (JWST), researchers have captured the most detailed and longest observation yet of this turbulent cosmic entity.

The black hole, with a mass four million times that of the Sun, is surrounded by a swirling disk of gas and dust known as an accretion disk. This disk fuels the black hole’s chaotic activity, generating unpredictable bursts of energy across multiple wavelengths.

Sagittarius A* is not just another distant celestial object—it’s an astrophysical laboratory, allowing scientists to explore how black holes interact with their environments. The variability of its emission, spanning from radio waves to X-rays, offers insight into the physics governing these extreme regions of space.

Unlike other black holes, Sagittarius A* never settles into a steady state. Instead, it produces flares that range from faint flickers lasting seconds to intense eruptions that persist for months.

This continuous activity is unusual. “Flares are expected to happen in essentially all supermassive black holes, but our black hole is unique,” said Farhad Yusef-Zadeh, a Northwestern University astrophysicist leading the study. “It is always bubbling with activity and never seems to reach a steady state. We observed the black hole multiple times throughout 2023 and 2024, and we noticed changes in every observation.”

The research, soon to be published in The Astrophysical Journal Letters, highlights the unpredictable nature of Sagittarius A* and raises new questions about the mechanisms fueling its variability.

To capture this activity, the researchers used JWST’s near-infrared camera (NIRCam), which observed Sagittarius A* for 48 hours over multiple sessions. These long-duration observations provided an unprecedented look at the black hole’s behavior over time.

The findings were surprising. “In our data, we saw constantly changing, bubbling brightness,” Yusef-Zadeh explained. “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.”

On average, Sagittarius A* produced five to six major flares per day, along with numerous smaller bursts. The variability of these flares was unexpected, with no clear periodicity or repetition. This randomness suggests complex physical processes at work, possibly involving changes in the accretion disk’s structure or interactions within its extreme magnetic environment.

While the precise cause of these emissions remains unclear, scientists suspect multiple processes are at play. Short-lived, faint flickers may result from minor disturbances within the accretion disk. Turbulent fluctuations in the plasma—a hot, ionized gas surrounding the black hole—could momentarily compress and heat the material, causing brief flashes of light.

“It’s similar to how the Sun’s magnetic field gathers together, compresses, and then erupts in a solar flare,” Yusef-Zadeh said. “Of course, the processes are more dramatic because the environment around a black hole is much more extreme.”

Brighter, longer-lasting flares likely originate from magnetic reconnection events—phenomena where twisted magnetic fields snap and release energy. This process accelerates charged particles to nearly the speed of light, producing intense bursts of radiation. Similar reconnection events occur in the Sun’s corona, but near a black hole, they unfold in a much more energetic and chaotic setting.

Magnetohydrodynamic (MHD) simulations, which model the behavior of plasma and magnetic fields around black holes, predict such variability over a range of time scales. These models suggest that changes in magnetic field strength and plasma density near the event horizon contribute to the dynamic nature of Sagittarius A*.

One of the study’s most intriguing discoveries came from analyzing the flares at two separate wavelengths—2.1 and 4.8 microns. JWST’s NIRCam allowed researchers to track these emissions simultaneously, providing a more detailed view of how the black hole’s activity evolves over time.

Unexpectedly, the shorter-wavelength emissions peaked slightly before the longer-wavelength emissions, with delays ranging from a few seconds to 40 seconds. This lag provides valuable information about the energy loss of particles as they spiral around magnetic field lines.

“This is the first time we have seen a time delay in measurements at these wavelengths,” Yusef-Zadeh said. “It suggests that particles lose energy throughout the flare, affecting different wavelengths at different rates.”

The ability to observe Sagittarius A* across multiple wavelengths has revolutionized scientists’ understanding of its emissions. Previous observations using the Keck Observatory, the Very Large Telescope (VLT), and the Spitzer Space Telescope provided important insights, but JWST’s long-duration observations allow for a more continuous and detailed look at the black hole’s behavior.

Despite this progress, questions remain. How do these flares relate to the long-term evolution of the black hole’s accretion disk? Do they follow hidden cycles that are yet to be uncovered? Future observations could provide answers.

Yusef-Zadeh and his team have proposed an uninterrupted 24-hour observation period using JWST, hoping to refine their understanding of the black hole’s variability. By reducing observational noise, they aim to detect faint features that might reveal underlying patterns in Sagittarius A*’s activity.

“When you are looking at such weak flaring events, you have to compete with noise,” Yusef-Zadeh said. “If we can observe for 24 hours, then we can reduce the noise to see features that we were unable to see before.”

The study of Sagittarius A* offers a rare glimpse into the workings of a supermassive black hole. As JWST continues to push the boundaries of observational astronomy, researchers are uncovering new complexities within these enigmatic objects, shedding light on the extreme physics that govern the universe’s most mysterious regions.

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