The James Webb Space Telescope (JWST) has provided astronomers with unprecedented mid-infrared observations of Sagittarius A (Sgr A ), the supermassive black hole at the center of our galaxy. These new insights are helping scientists unravel the mystery behind the flares emitted by this cosmic giant, and further illuminate the role of magnetic fields in shaping the matter around black holes.
Bridging the Gap in Black Hole Observations
For years, scientists have studied black hole flares across various wavelengths – near-infrared, radio, and others – each offering a unique perspective on these energetic events. The problem was a missing piece: mid-infrared data. This gap hindered a complete understanding of how flares evolve and the mechanisms driving them. The JWST’s observations, first revealed in January 2025, fill this void, linking infrared and radio wavelengths with critical mid-infrared data.
According to Sebastiano von Fellenberg of the Max Planck Institute for Radio Astronomy, “The mid-infrared data is exciting, because, thanks to the new JWST data, we can close the gap between the radio and near infrared regimes, which had been a ‘gaping hole’ in the spectrum of Sgr A*.” This breakthrough confirms flares occur in the mid-infrared spectrum, which is not always consistent with radio observations.
Simultaneous Multi-Wavelength Analysis
The JWST’s capabilities allowed the team to observe the black hole at four different wavelengths simultaneously with a single instrument. This enabled them to measure the mid-infrared spectral index, a crucial step in understanding flare dynamics.
The key to this analysis lies in the behavior of high-speed electrons around the black hole. As they spiral along magnetic field lines, these electrons emit synchrotron radiation – a byproduct of magnetic reconnection and energy release. The new observations confirm a process called “synchrotron cooling,” where these electrons lose energy, powering the observed mid-infrared emissions.
Measuring Magnetic Field Strength
This confirmation is significant because it allows for an independent measurement of magnetic field strength around Sgr A*. Previous measurements relied on other parameters, such as electron density, making them less precise. Von Fellenberg explains that the new method is “quite ‘clean’ in that not a lot of assumptions have to go into the measurement,” providing valuable data for theoretical models that have been poorly constrained in this regard.
The fact that magnetic field strengths are crucial to understanding how black holes function makes this discovery a step forward in astrophysics.
The Importance of Space-Based Observation
These observations would not have been possible without the JWST. The atmosphere interferes with ground-based mid-infrared observations, and the telescope’s Mid-Infrared Instrument (MIRI), operating in Medium-Resolution Spectrometer (MRS) mode, provides the necessary sensitivity and wavelength coverage to measure the spectral index.
As von Fellenberg puts it, “In order to get such high sensitivity in the mid-infrared, one needs to go to space… In addition, the MIRI/MRS instrument is the first instrument to give you such broad wavelength coverage for Sgr A*, a prerequisite to measure the spectral index, so it’s really a double whammy!”
In conclusion, the JWST’s mid-infrared observations of Sagittarius A* provide critical new data on black hole flare dynamics, allowing scientists to measure magnetic field strength with unprecedented accuracy. This breakthrough is a testament to the power of space-based telescopes and will refine our understanding of these enigmatic cosmic objects.
