The EHT Collaboration created possible images of Sagittarius A* using ray tracing, which predicts what black holes look like based on Einstein’s theory of general relativity.
(Image credit: Ben Prather/EHT Theory Working Group/Chi-Kwan Chan)
To understand the bizarre physics of the environment of Sgr A*, the imaging team used tools and models to measure the properties that were observed. They also developed more simplified models “that we can fit directly to the EHT data,” Harvard and Smithsonian astrophysicist Michael Johnson told reporters after the black hole’s imaging was announced on May 12, 2022.
“This is a different approach than imaging,” Johnson said. “It gives us a different perspective, and it lets us understand the systematic biases of both methods because these simple models are easier to constrain with very limited data.”
There were two ways they worked with the models. The first was to divide the data by time and to fit them to snapshots of the black hole in action, to make sure the measurements weren’t “contaminated” by variability in its environment. This was combined into a single, averaged-out model.
The second model sought to fit all the data in at the same time. “Here, we’re fitting for the average image structure, along with an extra source of variability noise that’s sitting on top of that average,” Johnson said. “This procedure is very similar to what we did to make the images. By combining all of these different approaches, we were able to precisely characterize the properties of the ring.”
