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Astrophysicists have gotten their first direct look at how a supermassive black hole changes in appearance over time.
The black hole at the center of the galaxy M87, some 55 million light-years distant from Earth, was the first black hole to be photographed (SN: 10/4/19). That image, created with data from the Event Horizon Telescope from April 2017, showed an unbalanced ring of light – the shadow of the black hole in the accretion disk of hot, bright plasma swirling in it. A new comparison of that image with previous data from the Event Horizon Telescope reveals that the brightest point in the ring changes location, due to turbulence in the violent swirl of material around the black hole, researchers report online on 23 May. September in the Astrophysical Journal.
“It’s a very exciting result,” says astrophysicist Clifford Will of the University of Florida in Gainesville, who was not involved in the study. “The first image they produced was just a snapshot. What we would really like to do is understand more about the dynamics of what is happening at the center of that galaxy. “
The Event Horizon Telescope, or EHT, is a network of radio telescopes that collectively make observations with a much higher resolution than any single observatory alone (SN: 10/4/19). An early version of the EHT began observing M87’s black hole, named M87 *, in 2009. At the time, the network included telescopes at just three sites in Arizona, Hawaii and California. In 2013, an observatory in Chile joined the team. But the network didn’t have enough telescopes to create a complete image of a black hole until 2017, when the EHT looked at M87 * with seven observatories in North America, South America, Hawaii, and Europe.
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Using the 2017 image of M87 * as a starting point for the appearance of the black hole, along with preliminary data from 2009 to 2013 to fill in some of the details, the EHT team was able to get a rough idea of what M87 * looked like during the early years of EHT observation.
Although the diameter of the black hole remained the same, the brightest point in the ring spun. The right side of the ring was brighter in 2013, while the bottom was brighter in 2017. “I think a lot of people in the (EHT) collaboration were surprised by the amount of variability,” says EHT team member Maciek Wielgus , an astrophysicist at Harvard University. The ring’s uneven flare arises from the tumultuous flow of superhot plasma around the black hole.
Preliminary data from the Event Horizon Telescope reveals how the brightest point in the ring of light around M87’s black hole changes over time. The researchers compared the actual image (far right), created from observations taken in 2017, with simulations of what the black hole previously looked like based on preliminary data from 2009 to 2013. The changes are due to turbulence in the storm of Swirling dungeon material.M. Wielgus, D. Pesce
This turbulence in the accretion disk, and therefore the variation in the appearance of the ring, is expected to depend on factors such as how fast the black hole spins, the inclination of its rotation, and the strength of its magnetic fields, says the Yale astrophysicist Priyamvada Natarajan. University, which did not participate in the study (SN: 1/30/17). Tracking changes in the appearance of M87 * can reveal new information about the nature of the black hole.
The new results show promise of using the EHT to probe the tempest around M87 *, says Harvard University astrophysicist Avi Loeb, who was not involved in the work. But rough sketches of the black hole’s appearance from 2009 to 2013 don’t contain enough information to draw firm conclusions about what is happening in this chaotic region, he says.
The EHT team will need more comprehensive images of M87 *, such as the one created from the 2017 data, to discover detailed changes over time. That series of still images could also be used to create an M87 * movie (SN: 12/16/19).
The EHT team is currently analyzing data collected in 2018, including observations from a newcomer to the EHT network, the Greenland Telescope. The EHT did not observe in 2019 or 2020, but “we will be observing in 2021, if COVID allows,” says EHT team member Geoffrey Bower, an astrophysicist at the Academia Sinica Institute of Astronomy and Astrophysics in Hilo, Hawaii (SN: 4 / 10/20). “We hope to have incredible image quality from that 2021 data,” he says, because by then the EHT will have two more eyes in the sky: the Kitt Peak observatory in Arizona and the NOEMA array in the French Alps. “I think that’s really going to get to the heart of the turbulence in the accretion region,” he says.
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