FRANKFURT. Six years after the historic release of the first-ever image of a black hole, the Event Horizon Telescope (EHT) Collaboration unveils a new analysis of the supermassive black hole at the heart of the galaxy M87, known as M87*. This analysis combines observations made in 2017 and 2018, and reveals new insights into the structure and dynamics of plasma near the event horizon.

This research represents a significant leap forward in our understanding of the extreme processes governing black holes and their environments, providing fresh theoretical insights into some of the universe's most mysterious phenomena. “The black hole accretion environment is turbulent and dynamic. Since we can treat the 2017 and 2018 observations as independent measurements, we can constrain the black hole’s surroundings with a new perspective,” says Hung-Yi Pu, assistant professor at National Taiwan Normal University. “This work highlights the transformative potential of observing the black hole environment evolving in time.”

The 2018 observations confirm the presence of the luminous ring first captured in 2017, with a diameter of approximately 43 microarcseconds – consistent with theoretical predictions for the shadow of a 6.5-billion-solar-mass black hole. Notably, the brightest region of the ring has shifted 30 degrees counter-clockwise. “The shift in the brightest region is a natural consequence of turbulence in the accretion disk around the black hole,” explains Abhishek Joshi, Ph.D. candidate at the University of Illinois Urbana-Champaign. “In our original theoretical interpretation of the 2017 observations, we predicted that the brightest region would most likely shift in the counterclockwise direction. We are very happy to see that the observations in 2018 confirmed this prediction!”

The fact that the ring remains brightest on the bottom tells us a lot about the orientation of the black hole spin. Bidisha Bandyopadhyay, a Postdoctoral Fellow from Universidad de Concepción adds: “The location of the brightest region in 2018 also reinforces our previous interpretation of the black hole’s orientation from the 2017 observations: the black hole’s rotational axis is pointing away from Earth!”

Luciano Rezzolla, chair of theoretical astrophysics at Goethe University Frankfurt, Germany, remarks that “ black holes as gigantic as M87* are expected to change only on very long timescales and it is not surprising therefore that much of what we have measured on 2017 has emerged also with observations made in 2018. Yet, the small differences we have found are very important to understand what is actually happening near M87*. To use an equivalent that may help, we do not expect to see a difference in the structure of the rock when comparing two photos of Mount Everest taken with a separation of one year. However, we do expect to see differences in the clouds near the peak and we can use them to deduce, for instance, the direction of dominant winds or the three-dimensional properties of the rock that we cannot deduce from a simple two-dimensional photo. This is what we have done in our theoretical analysis of the new data, much of which has been done in Frankfurt, and which has allowed us to better understand how matter falls onto M87* and the actual properties of M87* as a black hole. More of these observations will be made in the coming years and with increasing precision, with the ultimate goal of producing a movie of what actually happens near M87*.”

Using a newly developed and extensive library of super-computer-generated images — three times larger than the library used for interpreting the 2017 observations — the team evaluated accretion models with data from both the 2017 and 2018 observations. “When gas spirals into a black hole from afar, it can either flow in the same direction the black hole is rotating, or in the opposite direction. We found that the latter case is more likely to match the multi-year observations thanks to their relatively higher turbulent variability,” explains León Sosapanta Salas, a PhD candidate at the University of Amsterdam. “Analysis of the EHT data for M87 from later years (2021 and 2022) is already underway and promises to provide even more robust statistical constraints and deeper insights into the nature of the turbulent flow surrounding the black hole of M87.”

The EHT collaboration involves more than 400 researchers from Africa, Asia, Europe, and North and South America. The international collaboration is working to capture the most detailed black hole images ever obtained by creating a virtual Earth-sized telescope. Supported by considerable international investment, the EHT links existing telescopes using novel systems, creating a fundamentally new instrument with the highest angular resolving power that has yet to be achieved.

The individual telescopes involved are ALMA, APEX, the IRAM 30-meter Telescope, the IRAM NOEMA Observatory, the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope (LMT), the Submillimeter Array (SMA), the Submillimeter Telescope (SMT), the South Pole Telescope (SPT), the Kitt Peak Telescope, and the Greenland Telescope (GLT). Data were correlated at the Max-Planck-Institut für Radioastronomie (MPIfR) and MIT Haystack Observatory. The postprocessing was done within the collaboration by an international team at different institutions.

The EHT consortium consists of 13 stakeholder institutes: the Academia Sinica Institute of Astronomy and Astrophysics, the University of Arizona, the University of Chicago, the East Asian Observatory, Goethe University Frankfurt, Institut de Radioastronomie Millimétrique, Large Millimeter Telescope, Max Planck Institute for Radio Astronomy, MIT Haystack Observatory, National Astronomical Observatory of Japan, Perimeter Institute for Theoretical Physics, Radboud University, and the Smithsonian Astrophysical Observatory.