“We want to understand physics in the extreme conditions in the vicinity of a black hole and learn about how the black hole interacts with the matter in its immediate environment,” says Maciek Wielgus, an astronomer with the Harvard-Smithsonian Center for Astrophysics and the lead author of the new study. “Studying the dynamics of the crescent-like appearance of a black hole is a way to probe this fascinating environment.”
Before the EHT, scientists didn’t have the sensitive tools needed to study the structural changes a black hole goes through. “It was like watching a movie with a 1-pixel resolution,” says Wielgus. “You see that the brightness is changing in time—clearly something is going on there—but good luck figuring out what the movie is about.”
The new findings don’t make new observations of M87*, but rather characterize the shadow crescent through a new analysis of data collected from 2009 to 2013 during the EHT’s early days, combined with the 2017 data set that led to the image of the black hole in the first place. The older data was less detailed because of software constraints and more limited hardware, but it spanned a longer period of time. Meanwhile, the newer data set consisted of just four observations of M87* over one week, but it was much richer and more nuanced. Wielgus and his team were able to use details from the new data to fill in gaps in the old, as you might add a new corrective filter to an old photo to make it sharper. Bam—they had a high-quality time-lapse of M87*, over time scales stretching for several weeks.
The EHT is still processing the 2018 observations and plans to run new observations of M87 next year, using 10 telescopes in total. Those observations, which will involve a deeper study of the crescent, could reveal new insights into the spin of a black hole, the strength of its magnetic field, and the plasma microphysics of the surrounding matter. In turn, researchers hope those insights can be part of a bigger body of work that solves the mystery behind some of the wildest phenomena involved in supermassive black holes, like what drives the ejection of highly ionized matter from their center.