The James Webb Space Telescope (JWST) has revealed an ongoing, rapid-fire light show. This relates to new observations about the central supermassive black hole (Sagittarius A*) within our own galaxy. The unusual phenomenon was detected for 48 hours total across one year.
Astrophysicists from Northwestern University found the accretion disk (the swirling disk of gas and dust) orbiting the black hole is constantly emitting flares without periods of rest.
While some flares are faint flickers, lasting mere seconds, other flares are blindingly bright eruptions, which spew daily. There also are even fainter flickers that surge for months at a time. The level of activity occurs over a wide range of time — from short interludes to long stretches.
Further observations showed that events observed at the shorter wavelength changed brightness slightly before the longer-wavelength events.
Sagittarius A* was more active than anticipated. The accretion disk surrounding the black hole generated five to six big flares per day and several small sub-flares in between.
The findings took advantage of the JWST’s near infrared camera (NIRCam), which can simultaneously observe two infrared colors for long stretches of time. With the imaging tool, the researchers observed Sagittarius A* for a total of 48 hours — in 8-to-10-hour increments across one year. This enabled scientists to track how the black hole changed over time.
The 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.
According to lead scientist Farhad Yusef-Zade: “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 astrophysicists do not 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 thinks that minor disturbances within the accretion disk likely generate the faint flickers. Specifically, turbulent fluctuations within the disk can compress plasma (hot, electrically charged gas) to cause a temporary burst of radiation.
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, these particles emit bright bursts of radiation.
With the smaller bursts, it could be that the particles lose energy over the course of the flare — losing energy quicker at shorter wavelengths than at longer wavelengths. Such changes are expected for particles spiraling around magnetic field lines.
The research appears in The Astrophysical Journal Letters. The research is titled “Non-stop variability of Sgr A* using JWST at 2.1 and 4.8 micron wavelengths: Evidence for distinct populations of faint and bright variable emission”.
