Tracking a black hole’s evolution in time: M87* one year later

Six years ago, the Event Horizon Telescope (EHT) released the world’s first image of a black hole. Based on observations made in 2017, that image made headlines around the world. It was the result of a global effort, coordinating multiple radio telescopes and researchers all working together to observe M87*, a supermassive black hole some 55 million light years away. More images followed, including those released last year based on 2018 observations. Now, a new analysis of these observations marks a major step forward in unravelling the complex dynamics of black holes.

In the paper, published today in Astronomy & Astrophysics, researchers confirmed that M87*’s rotational axis points away from Earth and demonstrated that turbulence within the accretion disk – rotating gas around the black hole – can help explain the observed shift in the fiery ring compared to the 2017 images.

“We started to see changes, and that's exactly what we would have expected. M87*’s event horizon is about a light-day across, so its accretion disk should present a new version of itself on a timescale of just a few days,” says Avery Broderick, Research Associate Faculty at Perimeter Institute and Associate Professor at the University of Waterloo who leads the team processing the EHT data. “All our simulated models give us some sense for how much it should be varying, and this is an important confirmation. This paper is about understanding what these images mean in the context of our best numerical simulations.”

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.”

When that first image was released, the brightest section was further south on the image than scientists thought it would be. It constituted a small mystery that needed more data to solve. When they compared 2017 observations with the 2018 ones, the team could see it reverted to the mean, ensuring their modelling and observations were aligned.

“It's all about reproducibility. We expected M87* to change. It did change,” says Broderick. “The fact that that it changed essentially the way we thought it would reaffirms this critical component of science: reproducibility.”

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 researcher 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!”

The worldwide effort to capture black holes

Taking a picture of a black hole – and studying its evolving properties – is no small feat. In fact, it takes a telescope the size of our entire planet to do it. The EHT achieves this by coordinating multiple radio telescopes around the globe, all observing the same black hole at the same time, and then processing that data into something that can be displayed visually.

“The EHT is the highest resolution imaging instrument in the history of science,” explains Broderick. “The resolution of these images is comparable for holding your thumb out at arm's length and being able to see the atoms in your thumb.”

To capture that resolution, petabytes of data are required. Literal tons of hard drives work together to process and analyze the information. After the 2017 observations, the project was in danger of running out of data storage, recalls Broderick. “We had all that data at the end of 2017 and we needed a whole new set of hard drives that we didn’t have. Perimeter entered the fray and made a last-minute purchase of hard drives, filling a critical gap that made it possible not to cancel the 2018 observations. The very fact that these observations happened is a consequence of Perimeter’s timely and critical involvement, and the flexibility that Perimeter can bring to these efforts.”

But the EHT isn’t just about the technology or hard drive space. It’s also about the next generation of physicists, and fostering the talent needed to make the next big discovery. Perimeter Institute and the University of Waterloo have played a critical role in developing that talent and sending them off to do great work.

“A lot of the 2018 analysis was led by our colleagues at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) in Taiwan. Interestingly, the people that led both the paper that came out last January and the one that came out today came through Waterloo as students and postdoctoral researchers.” says Broderick. “We’re training the next generation of leaders in EHT.” 

The analysis released today is the result of a planet’s worth of talent, technology, and effort. That famous image of a “fiery doughnut,” as Broderick puts it, captures more than a black hole. It captures a planet’s worth of cooperation.

“(EHT) requires an Earth-sized telescope. That means we need people across the globe, from people who build things with their hands to people who build theories on their chalkboards, and everything in between,” says Broderick. “This is a demonstration of what humans can do if we can work together. It is possible to set aside differences and do extraordinary things.”

About the Event Horizon Telescope Collaboration

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.