Black hole at center of Milky Way’s puts on daily ‘fireworks show’

By Stephen Beech

The supermassive black hole at the Milky Way's center is providing a round the clock "fireworks" display on an unprecedented scale.

New observations using NASA's James Webb Space Telescope (JWST) reveal a "unique" ongoing, rapid-fire light show.

An international team of astrophysicists, led by scientists at Northwestern University in Illinois, US, has gained the longest, most detailed glimpse yet of the void that lurks in the middle of our galaxy.

They found that the swirling disk of gas and dust orbiting the central supermassive black hole - called Sagittarius A* - is emitting a "constant" stream of flares with no periods of rest.

While some flares are faint flickers, lasting mere seconds, others are "blindingly bright" eruptions, which spew daily.

The study, published in The Astrophysical Journal Letters, shows that there also are even fainter flickers that surge for months at a time.

Scientists say the level of activity occurs over a wide range of time — from short interludes to long stretches.

Their findings could help physicists better understand the fundamental nature of black holes, how they interact with their surrounding environments and the dynamics and evolution of our own galactic home.

Study leader Northwestern Professor Farhad Yusef-Zadeh said: “Flares are expected to happen in essentially all supermassive black holes, but our black hole is unique.

“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.

"We saw something different each time, which is really remarkable. Nothing ever stayed the same.”

The research team used the JWST’s near-infrared camera (NIRCam), which can simultaneously observe two infrared colors for long stretches of time.

With the imaging tool, they observed Sagittarius A* for a total of 48 hours — in eight- to 10-hour increments across one year, enabling them to track how the black hole changed over time.

While Yusef-Zadeh expected to see flares, he said Sagittarius A* was "more active" than he anticipated.

He explained that the observations revealed "ongoing fireworks" of various brightness and durations.

The accretion disk surrounding the black hole generated five to six big flares per day and several small sub-flares in between.

Yusef-Zadeh said: “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. It appears to be random.

"The activity profile of the black hole was new and exciting every time that we looked at it.”

Although scientists don't yet fully understand the processes at play, Yusef-Zadeh suspects two separate processes are responsible for the short bursts and longer flares.

If the accretion disk is a river, then the short, faint flickers are like small ripples that fluctuate randomly on the river’s surface.

The longer, brighter flares, however, are more like tidal waves, caused by more significant events.

Yusef-Zadeh suggests that minor disturbances within the accretion disk likely generate the faint flickers.

Specifically, turbulent fluctuations within the disk can compress plasma - a hot, electrically charged gas - to cause a temporary burst of radiation.

Yusef-Zadeh likens the event to a solar flare.

He said: “It’s similar to how the sun’s magnetic field gathers together, compresses and then erupts a solar flare.

“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.”

Yusef-Zadeh attributes the big, bright flares to magnetic reconnection events — a process where two magnetic fields collide, releasing energy in the form of accelerated particles.

Traveling at velocities near the speed of light, the particles emit bright bursts of radiation.

Yusef-Zadeh said: “A magnetic reconnection is like a spark of static electricity, which, in a sense, also is an ‘electric reconnection."

Because the JWST’s NIRCam can observe two separate wavelengths at the same time, the team were able to compare how the flares’ brightness changed with each wavelength.

Yusef-Zadeh explained that capturing light at two wavelengths is like “seeing in color instead of black and white.”

By observing Sagittarius A* at multiple wavelengths, the research team captured a more complete picture of its behavior.

They were surprised to discover that events observed at the shorter wavelength changed brightness slightly before the longer-wavelength events.

Yusef-Zadeh said: “This is the first time we have seen a time delay in measurements at these wavelengths.

“We observed these wavelengths simultaneously with NIRCam and noticed the longer wavelength lags behind the shorter one by a very small amount - maybe a few seconds to 40 seconds.”

He says the time delay provided more clues about the physical processes occurring around the black hole.

One explanation is that the particles lose energy over the course of the flare - losing energy quicker at shorter wavelengths than at longer wavelengths.

Now Yusef-Zadeh hopes to use the JWST to observe Sagittarius A* for a longer period of time.

He added: “When you are looking at such weak flaring events, you have to compete with noise.

“If we can observe for 24 hours, then we can reduce the noise to see features that we were unable to see before. That would be amazing.

"We also can see if these flares are truly random.”