Meet the supermassive black hole at the centre of our galaxy
23 May 2022
Scientists have captured humanity’s first look at the supermassive black hole, called Sagittarius A* (Sgr A*), that is at the centre of our home galaxy, the Milky Way. The Sgr A* black hole image was captured and created by a team of more than 300 researchers from 80 institutes around the world called the Event Horizon Telescope Collaboration. Modelling methods applying probability were used to develop an average of 2017 different observations.
This is the first image of Sagittarius A* (Sgr A*), the supermassive black hole at the centre of our galaxy. The Sgr A* black hole image was captured by the Event Horizon Telescope and is an average of the different images.
Avery Broderick, a professor at the University of Waterloo and an associate faculty member at Perimeter Institute for Theoretical Physics, is part of the international Event Horizon Telescope (EHT) collaboration that imaged the black hole, and he played a key role in interpreting the image data.
At this distance, imaging Sgr A* is akin to reading a newspaper in Los Angeles from a park bench in Manhattan.
The new image of Sgr A* will allow the EHT scientists to compare black holes. Sgr A* is the second black hole to be captured by the EHT collaboration. In 2019, the team released a landmark image of a much larger, more distant black hole in the Messier 87 galaxy (M87*).
“Despite being 1,500 times smaller than M87*, the new images of Sgr A* look remarkably similar to those of M87*,” said Broderick, who holds the Delaney Family John Archibald Wheeler Chair at Perimeter Institute. “Nobody knew for sure if enormous black holes and relatively smaller ones would share much in common, but now we have two unique black holes to compare, so we can better understand how black holes of different sizes eat, how they grow, and how they shape the galaxy around them.”
Since Sgr A* is significantly smaller than M87*, the light orbits around the black hole in considerably less time than the larger black hole. This created a challenge for the researchers as, over the observation period, Sgr A* experienced a large amount of variability in the data, which required completely new image analysis methods compared to those used for M87*.
Broderick’s role in the EHT collaboration was at the forefront of the image analysis work. His team developed image modelling methods based on probability, known as Bayesian images, to address this variability. Broderick’s method used probability to identify the features of this black hole and was able to conclude that Sgr A* had a bright ring and a dark centre.
The images captured by the EHT researchers show the dark central region from which light cannot escape. A fiery ring of superheated gases swirling around the periphery of the black hole, light barely escaping to begin its journey across 27,000 light-years to the EHT telescopes.
At this distance, imaging Sgr A* is akin to reading a newspaper in Los Angeles from a park bench in Manhattan. The EHT collaboration captured detailed imagery and data about the supermassive black hole by creating a network of precision-timed telescopes at sites spanning the globe; all zeroed in on the powerful gravitational source at the Milky Way’s core.
“The Event Horizon Telescope is a remarkable demonstration of the power of international scientific collaboration,” said Perimeter Institute Director Robert Myers. “Black holes were once only a theoretical playground for mathematical physicists. But the EHT collaboration has transformed black holes from theoretical ideas into objects for empirical observation and study. Perimeter is proud to be part of this unprecedented scientific endeavour, which is still just getting started.”
Sgr A* is four million times more massive than our sun but had never been directly detected because black holes are literally black – they exert such gravitational force that even light cannot escape their grip. Sgr A* is much too far away to affect us on Earth, but it has cataclysmic effects on its nearer surroundings. Understanding the inner workings of black holes is crucial to testing, and perhaps revising our best theory of gravity, Einstein’s general relativity.
“Now, more than ever, the world is looking to scientists for an understanding of the world around us, and these ground-breaking images inspire a deeper fascination and curiosity about our universe,” said Bob Lemieux, Dean of Science at the University of Waterloo. “We are very proud of Avery’s leadership and dedication to the EHT collaboration and look forward to seeing the transformative work he continues to do at Waterloo.”
More than 300 researchers from 80 institutes around the world called the Event Horizon Telescope Collaboration produced the image by using observations from a worldwide network of radio telescopes. The Sgr A* black hole image is an average of the different images the EHT Collaboration has extracted from its 2017 observations.