From the initial conception of black holes in the writings of natural philosopher John Michell in 1783 to the theories and equations of Albert Einstein and Karl Schwarzchild in the early 1900s, the mysteries surrounding them have fascinated and eluded us for centuries. Black holes—cosmic bodies so massive that not even light can escape their gravitational pull—have long been a mainstay in science fiction, used as plot devices in literature from writers such as Arthur C. Clarke and Larry Niven and film and TV properties such as Star Trek and Interstellar (among many others). But in the real world, black holes have remained a puzzle for scientists to solve and a general curiosity that continues to inspire creativity and a dedicated presence in popular culture.
Some of those puzzle pieces are now beginning to come together with the recent announcement on April 10, 2019, from the Event Horizon Telescope that astronomers had captured the first true image of a black hole.
The Event Horizon Telescope (EHT) itself is actually an array of eight ground-based radio telescopes from around the world that use interferometry to simultaneously combine images with the specific purpose of capturing a black hole. The EHT’s success reflects the spirit of collaboration from researchers and organizations across the globe who have come together to work on this project.
“This is an extraordinary scientific feat accomplished by a team of more than 200 researchers,” EHT project director Sheperd Doeleman, of the Harvard-Smithsonian Center for Astrophysics, said in the announcement.
Through gazing into the far reaches of the cosmos, the EHT arrays compiled the image from its observations of the distant Messier 87 (M87) galaxy, roughly 55 million light-years from Earth amidst the constellation Virgo. The image itself shows a bright ring surrounding the near-circular darkness of the black hole itself, evidence of light bending under the intensity of the black hole’s gravity well.
Heino Falcke of Radboud University in the Netherlands, chair of the EHT Science Council, explained: “If immersed in a bright region, like a disc of glowing gas, we expect a black hole to create a dark region similar to a shadow—something predicted by Einstein’s general relativity that we’ve never seen before. This shadow, caused by the gravitational bending and capture of light by the event horizon, reveals a lot about the nature of these fascinating objects and allowed us to measure the enormous mass of M87’s black hole.”
The sheer size and mass of the M87 black hole are not only impressive but difficult for many to even to comprehend. According to Suresh Sreenivasan of the Minnesota Astronomical Society (MAS), it has a mass several billion times that of our own sun. “In the process of gobbling up nearby matter, it unleashes a violent jet of X-rays and other particles out 5,000 light-years that is powerful enough that we can see it through telescopes here on Earth,” Sreenivasan says. “While some black holes are suspected to be tiny, even microscopic, this one would stretch all the way to the Kuiper Belt—four times the distance to Neptune—if it were located where the sun is.”
The black hole image serves as another confirmation of Einstein’s theory of general relativity, which led scientists to speculate that massive objects could break down and become black holes that could effectively collapse space-time, trapping matter and light while bending and breaking the laws of physics as we know them. It builds on the 2015 accomplishment by the Laser Interferometer Gravitational-Wave Observatory (LIGO) of recording the sound of gravitational waves—ripples in the fabric of space-time—produced by the merger of a binary black hole. Essentially, we now have both the sound and the sight to prove Einstein’s theories.
An achievement of this magnitude will undoubtedly have lasting impacts, inspire closer looks, and change the course of research in this field for years to come. “We have achieved something presumed to be impossible just a generation ago,” Doeleman concluded in his statement. “Breakthroughs in technology, connections between the world’s best radio observatories, and innovative algorithms all came together to open an entirely new window on black holes and the event horizon.”
And while this was a team effort combining the expertise of numerous scientists from across the globe, according to MAS president Dave Falkner, it’s important to note that it was the algorithm written by Katie Bouman, now an assistant professor of computing and mathematical sciences at the California Institute of Technology, while she was a graduate student at MIT that allowed the images from all of the telescopes involved to be combined into the image that has been all over the Internet since its release.
The announcement is detailed further in a series of six papers published in a special issue of the Astrophysical Journal Letters.