First-Ever Detection of Mid-IR Flares in Sgr A*- the Supermassive Black Hole at the Galactic Center

An international team of scientists, including CITA faculty Bart Ripperda and CITA graduate student Braden Gail, have made the first-ever detection of a mid-IR flare from Sgr A*.

This artist’s conception of the mid-IR flare in Sgr A* captures the variability, or changing intensity, of the flare as the black hole’s magnetic field lines approach each other. The byproduct of this magnetic reconnection is synchrotron emission. The emission seen in the flare intensifies as energized electrons travel along the SMBH’s magnetic field lines at close to the speed of light. (Credit: CfA/Mel Weiss)

Using the James Webb Space Telescope, an international team of scientists among whom CITA faculty Bart Ripperda and graduate student Braden Gail, detected for the first time a mid-IR flare from the supermassive black hole (SMBH) at the heart of the Milky Way galaxy.

Sgr A*— the Supermassive Black Hole (SMBH) at the centre of our galaxy, which is roughly 4 million times the mass of the Sun, has been the subject of scientific scrutiny 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, understand how it emits flares and on what timescale they occur. Despite a long history of successful observations, including imaging of this cosmic beast by the Event Horizon Telescope in 2022, one crucial piece of the puzzle— mid-IR observations— was missing until now.

The reported mid-IR detection happened during a flare that lasted about 40 minutes, a duration similar to NIR and X-ray flares. Infrared light is a type of electromagnetic radiation. It has longer wavelengths than visible light, but shorter wavelengths than radio light. Mid-IR sits in the middle of the IR spectrum, and allows astronomers to observe objects, such as 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 range, leaving a gap in scientists’ understanding of what causes flares and questions about whether their theoretical models are complete.

“The flare observed at centre of Milky Way with JWST was so well-monitored that we are not just able to infer the properties of the radiation but can learn something about the electrons that orbit the black hole and emit the photons. The data is so rich that we could really test our theories of how these flares work via simulations,” shared CITA faculty Bart Ripperda.

Scientists aren’t 100% sure what causes flares, so they rely on models and simulations, which they compare with observations to try to understand what causes flares. Many simulations suggest that the flares in Sgr A* are caused by the interaction of magnetic field lines in the SMBH’s turbulent accretion disk. When two magnetic field lines approach each other, they can change their configuration in a process known as “reconnection”. This releases a large amount of energy. A byproduct of this magnetic reconnection is the release of electromagnetic radiation known as “synchrotron emission”. The emission seen in the flare intensifies as energized electrons travel along the SMBH’s magnetic field lines at close to the speed of light.

“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,” said Joseph Michail, one of the lead authors on the paper and a NSF Astronomy and Astrophysics Postdoctoral Fellow at the CfA. “For over 20 years, we’ve known what happens in the radio and Near-infrared (NIR) ranges, but the connection between them was never 100% clear. This new observation in mid-IR fills in that gap.”

Braden Gail, a graduate student at the Canadian Institute for Theoretical Astrophysics, who ran simulations on a Canadian supercomputer, adds: “This kind of research is interesting because we’re able to probe the fundamental physics of how supermassive black holes accrete material, a process that is known to reshape and evolve galaxies like our own. The recent mid infrared observation, in addition to existing near infrared, x-ray, and radio, are all critical pieces in solving this puzzle. Discovering the variation in emission as the wavelength changes is particularly important in understanding how emitted energy from these flares evolve over time, helping us better understand and model the processes related to their creation and evolution.”

The observations, led by astronomers from the Center for Astrophysics | Harvard & Smithsonian (CfA), were presented today in a press conference at the 245th proceedings of the American Astronomical Society (AAS) in National Harbor, Maryland, and are accepted for publication in the Astrophysical Journal Letters (ApJL).

This artist’s conception of the mid-IR flare in Sgr A* captures the apparent movement of the flare as energized electrons spiral along the magnetic field lines of the supermassive black hole, and spike its intensity. These changes, or variability in intensity are known as synchrotron emission. (Credit: CfA/Mel Weiss)

Read more at: Astrophysics|Harvard & Smithsonian, UniverseToday, IFLScience, Max-Planck-Gesellschaft, Phys.org, A&S News, University of Toronto.

Contact:
Lyuba Encheva 
Communications and Events, CITA 
Email: lyuba@cita.utoronto.ca