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Using the MIRI instrument onboard of the James Webb Space Telescope, an international team of scientists made the first-ever detection of a mid-IR flare from Sagittarius A*, the supermassive massive black hole at the heart of the Milky Way. In simultaneous radio observations, the team found a radio counterpart of the flare lagging behind in time.
Sebastiano von Fellenberg from the Max Planck Institute for Radio Astronomy in Bonn, Germany, is the lead author of the paper.
Scientists have been actively observing Sagittarius A* (Sgr A*)— a supermassive black hole roughly 4 million times the mass of the Sun— since the early 1990s. Sgr A* regularly exhibits flares that can be observed in multiple wavelengths, allowing scientists to see different views of the same flare and better understand how it emits lights and how the emission is generated. Despite a long history of successful observations, and even imaging of the cosmic beast by the Event Horizon Telescope in 2022, one crucial piece of the puzzle— mid-infrared observations (Mid-IR) — was missing until now.
Infrared (IR) light is a type of electromagnetic radiation that has longer wavelengths than visible light, but shorter wavelengths than radio light. Mid-IR sits in the middle of the infrared spectrum, and allows astronomers to observe objects, like flares, that are often difficult to observe in other wavelengths due to impenetrable dust. Until the recent study, no team had yet successfully detected Sgr A*’s variability in the mid-IR, leaving a gap in scientists’ understanding of what causes flares, and questions about whether theoretical models are complete.
“Sgr A*’s flare evolves and changes quickly, in a matter of hours, and not all of these changes can be seen at every wavelength,” says Joseph Michail, one of the lead authors on the paper, a Postdoctoral Fellow at the Harvard CfA. “For over 20 years, we’ve known what happens in the radio and what happens in the near infrared, but the connection between them was never 100% clear or certain. This new observation in mid-IR fills in that gap and connects the two.”
Scientists aren’t 100% sure what causes flares, so they rely on models and simulations, which they compare with observations, to try to understand where they come from. Many simulations suggest that flares in Sgr A* are caused by the bunching of magnetic field lines in the supermassive black hole’s turbulent accretion disk. When two magnetic field lines approach they can connect to each other and release a large amount of their energy. The byproduct of this magnetic reconnection— synchrotron emission— occurs when energized electrons travel at speeds close to the speed of light along the magnetic field lines of the supermassive black hole. They emit high-energy radiation photons that power the flare.
Because the mid-IR spectral range sits between the submillimeter and the near-infrared (NIR), it is keeping secrets locked away about the role of electrons, which have to cool to release energy to power the flares. The new observations are consistent with the existing models and simulations, giving one more strong piece of evidence to support the theory of what’s behind the flares.
“Our research indicates that there may be a connection between the observed variability at millimeter wavelengths and the observed mid-IR flare emission,” says Sebastiano von Fellenberg, a postdoctoral researcher at the Max Planck Institute for Radio Astronomy (MPIfR) and the lead author on the new paper. He adds that the results underscore the importance of expanding multi-wavelength studies of not just Sgr A*, but other supermassive black holes, like M87*, to get a clear picture of what’s really happening within and beyond their accretion disks.
“While our observations suggest that Sgr A*’s mid-IR emission does indeed result from synchrotron emission from cooling electrons, there’s more to understand about magnetic reconnection and the turbulence in Sgr A*’s accretion disk,” says von Fellenberg. “This first-ever mid-IR detection, and the variability seen with the SMA, has not only filled a gap in our understanding of what has caused the flare in Sgr A* but has also opened a new line of important inquiry.”
Simultaneous observations with the Submillimeter Array (SMA), the Nuclear Spectroscopic Telescope Array (NuSTAR) and the Chandra X-ray Observatory filled in an additional part of the story. No flare was detected during the X-ray observations, likely because this particular flare didn’t accelerate electrons to energies as high as some other flares do. But the team was successful when they turned to the SMA, which detected a millimeter-wave flare lagging roughly 10 minutes behind the mid-IR flare.
"Working on reducing and calibrating the data from James Webb - which is presently one of the best telescopes we have - was a dream come true for me, and I'm really grateful to the Deutsche Akademische Austauschdienst for funding my internship work on this project at the MPIfR in Bonn during the summer, with the amazing mentorship of Sebastiano von Fellenberg and Gunther Witzel. I look forward to work further in this area by pursuing a PhD after graduating this year," says Tamojeet Roychowdhury, currently student from the Indian Institute of Technology in Bombay.
“We are building an increasingly detailed picture of the processes that take place in the immediate vicinity of a supermassive black hole. The quality of our mid-infrared data is yet another testament to the James Webb Space Telescope's enormous technical capabilities,” concludes Gunther Witzel, staff scientist at the MPIfR.
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Additional Information
JWST: The James Webb Space Telescope is the world’s premier space science observatory with a primary mirror of 6.50 m diameter. It is an international program led by NASA with its partners, ESA (the European Space Agency) and CSA (the Canadian Space Agency).
MIRI (Mid-Infrared Instrument) is an instrument on the James Webb Space Telescope. It includes a camera and a spectrograph observing mid to long infrared radiation from 5 to 28 microns. The MIRI consortium consists of the ESA member states Belgium, Denmark, France, Germany, Ireland, the Netherlands, Spain, Sweden, Switzerland, and the United Kingdom. The consortium's work is funded by the national science organisations, in Germany by the Max Planck Society (MPG) and the German Aerospace Center (DLR). The participating German institutions are the Max Planck Institute for Astronomy in Heidelberg, the University of Cologne, and Hensoldt AG in Oberkochen (formerly Carl Zeiss Optronics).
SMA: The Submillimeter Array (SMA) on the summit of Mauna Kea/Hawaii consists of eight radio dishes working together as one telescope. The SMA is operated jointly by the CfA and the Academia Sinica in Taiwan.
NUSTAR: The Nuclear Spectroscopic Telescope Array mission of NASA/JPL studies the universe in high energy X-rays to better understand the dynamics of black holes, exploding stars and the most extreme active galaxies.
Chandra: NASA’s Chandra X-ray Observatory is the world's most powerful X-ray telescope. It has eight-times greater resolution and is able to detect sources more than 20-times fainter than any previous X-ray telescope.
Harvard CfA: The Center for Astrophysics | Harvard & Smithsonian is a collaboration between Harvard and the Smithsonian designed to ask—and ultimately answer—humanity's greatest unresolved questions about the nature of the universe. The Center for Astrophysics is headquartered in Cambridge, MA, with research facilities across the U.S. and around the world.
The research team comprises Sebastiano Daniel von Fellenberg, Tamojeet Roychowdhury, Joseph M. Michail, Zach Sumners, Grace Sanger-Johnson, Giovanni G. Fazio, Daryl Haggard, Joseph L. Hora, Alexander Philippov, Bart Ripperda, Howard A. Smith, S. P. Willner, Gunther Witzel, Shuo Zhang, Eric E. Becklin, Geoffrey C. Bower, Sunil Chandra, Tuan Do, Mark A. Gurwell, Nicole M. Ford, Kazuhiro Hada, Sera Markoff, Mark R. Morris, Joey Neilsen, Nadeen B. Sabha, and Braden Seefeldt-Gail. The first two authors, Sebastiano von Fellenberg and Tamojeet Roychowdhury, and also Gunther Witzel are affiliated with the Max Planck Institute for Radio Astronomy (MPIfR). Tamojeet Roychowdhury was funded by the Deutsche Astronomische Austauschdienst (DAAD) for his work on the project at MPIfR.
Dr. Sebastiano Daniel von Fellenberg
Max Planck Institute for Radio Astronomy, Bonn
Fon: +49 228 525-456
E-mail: sfellenberg@mpifr-bonn.mpg.de
Dr. Gunther Witzel
Max Planck Institute for Radio Astronomy, Bonn
Fon: +49 228 525-358
E-mail: gwitzel@mpifr-bonn.mpg.de
First mid-infrared detection and modeling of a flare from Sgr A*, by Sebastiano D. von Fellenberg et al., published in: The Astrophysical Journal Letters on January 14, 2025 (DOI: xxx).
Preprint on arXiv Server: http://arxiv.org/abs/2501.07415
https://www.mpifr-bonn.mpg.de/pressreleases/2025/1
Light curve and three images of Sgr A* observed on April 06, 2024 with MIRI at the JWST. A, B and C ...
Sebastiano von Fellenberg (von Fellenberg et al., ApJ Letters 2025)
The MIRI instrument within the JWST Integrated Science Instrument Module (ISIM). MIRI is the silver ...
NASA/Goddard Space Flight Center/Chris Gunn (MIRI). NASA (JWST)
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Light curve and three images of Sgr A* observed on April 06, 2024 with MIRI at the JWST. A, B and C ...
Sebastiano von Fellenberg (von Fellenberg et al., ApJ Letters 2025)
The MIRI instrument within the JWST Integrated Science Instrument Module (ISIM). MIRI is the silver ...
NASA/Goddard Space Flight Center/Chris Gunn (MIRI). NASA (JWST)
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