American scientists have used a 3D technology similar to CT scans to reconstruct the energetic outbursts near the supermassive black hole at the center of the Milky Way, known as Sagittarius A*. The findings, published on April 22 in Nature Astronomy, offer clearer insights into how flares form around black holes.
Supercomputer simulations reveal that the material orbiting the black hole in an accretion disk periodically erupts in high-energy events known as flares, observable in X-rays, infrared, and radio wavelengths. However, reconstructing these flares' 3D structures from observational data has been challenging.
Aviad Levis and colleagues at the California Institute of Technology have developed a new imaging technique named "orbital polarization tomography," which is akin to the technology used in medical computed tomography (CT scans). Using observations from the Atacama Large Millimeter/submillimeter Array (ALMA) on April 11, 2017, the team studied the radio wavelength appearance of the flares in 3D. The reconstruction faced difficulties due to the distance and variations in brightness and particle details, prompting the use of a new computer technique based on neural networks, constrained by the predicted physical properties of black holes and electromagnetic radiation processes.
The resulting images suggest that the flares likely originate from two bright spots on the accretion disk, nearly face-on to Earth. These spots rotate clockwise around the black hole, with an orbital radius about half the distance from the Earth to the Sun (approximately 75 million kilometers). The reconstructed flare structure aligns with prior computer simulations, confirming our general understanding of the extreme environment surrounding black holes.
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