In 2019, the Event Horizon Telescope (EHT) collaboration, including a team of MIT Haystack observatory scientists, provided the first image of a black hole, revealing M87 * – the supermassive object at the center of the M87 galaxy. The EHT team used lessons learned last year to analyze archival data sets from 2009 to 2013, some of which had not been published before. The analysis reveals the behavior of the black hole image over several years, indicating the persistence of the crescent-like shadow feature, but also its diverging direction – the crescent appears to be wobbling. The full results appear today in the Astrophysical Journal in an article titled “Observing M87 * Morphology * in 2009-2017 with the Event Horizon Telescope.”
EHT is a global group of telescopes, making simultaneous observations using ultra-long fundamental interferometry technology. Together they form a virtual Earth-sized radio dish, providing uniquely high image resolution. In 2009-13, M87 * was observed by EHT prototype arrays, with telescopes located in three geographic locations from 2009 to 2012 and four locations in 2013. In 2017, EHT reached maturity with telescopes located in five distinct geographic locations across the globe floor.
The data sets for this research have been fully linked to the MIT Haystack Observatory. The 2009-2013 notes consist of less data than those conducted in 2017, which makes it impossible to generate an image. But the EHT team was able to use statistical modeling to look at changes in the M87’s appearance * over time. In the modeling approach, the data is compared with a family of geometric templates, in this case episodes of irregular brightness. Then a statistical framework is used to determine whether the data are consistent with these models and to find the best parameters of the model.
“This is a beautiful example of creative data analysis.” Colin Lonsdale, Director of the MIT Haystack Observatory and Chair of the EHT Cooperation Council, says that extracting an important new understanding of astrophysics and extracting new insights from previous observations is a fictional example of how scientists can maximize the information content of such data that has been made Hard-earned. “The behavior of this event horizon scale structure over a period of years allows for significant additional constraints to be placed on the properties of this remarkable object.”
Extending the analysis to include observations of 2009-2017, EHT scientists demonstrated that the M87 * adheres to theoretical predictions. The black hole’s shadow diameter remained consistent with Einstein’s theory of general relativity predicting a black hole of 6.5 billion solar masses.
“In this study, we show that the general shape, or the presence of an asymmetric ring, likely persists on multi-year timescales,” says Kazu Akiyama, research scientist at MIT Haystack Observatory and one of the project participants. “Consistency across multiple watch epochs gives us more confidence than ever in the nature of the M87 * and the origin of the shadow.”
Although the diameter of the crescent remained constant, the EHT team found the data was hiding a surprise: the ring is wobbly, meaning big news for the scientists. For the first time, they can get a glimpse of the dynamic structure of the accretion flow near a black hole’s event horizon, under conditions of extreme gravity. Studying this region holds the key to understanding phenomena such as relativity jets, and will allow scientists to formulate new tests of general relativity.
The temperature of the gas falling on the black hole rises to billions of degrees, and ionizes and becomes turbulent in the presence of magnetic fields. “Because the flow of matter is turbulent, the crescent appears to fluctuate over time,” says Masick Welgos of the Harvard and Smithsonian Center for Astrophysics, a fellow at the Black Hole Initiative and lead author of the paper. “In fact, we see a lot of variance there, and not all theoretical models allow for a lot of fluctuation. What it means is that we can start to exclude some models based on the observed source dynamics.”
“MIT Haystack has been helpful in organizing these early observations, correlating the massive amounts of data returned to large numbers of hard drives, and minimizing data,” says Vincent Fish, a research scientist at Haystack Observatory. “While we were able to place important limitations on the size and nature of the emission in the M87 * at the time, the images generated from the much better batch data of 2017 provided an important context for fully understanding what previous data was trying to tell us.”
Haystack scientist Jeff Crowe adds, “After working on EHT technology for a decade, I’m glad the M87 * is using its time so well.”