From “Star Trek” to “Interstellar,” black holes have captivated humans for generations. Now, researchers at the Event Horizon Telescope (EHT) project have made history by producing the first real image of a black hole.
The black hole in question, although a whopping 55 million light-years from Earth in a galaxy called Messier 87, was able to be photographed because of its massive size. It is believed to be 6.5 billion times the mass of our sun.
A black hole is the burned-out husk of a dead star, with a gravitational pull strong enough to warp the fabric of space and time. Nothing—not even light—can escape it. It is at the center of the black hole where all matter is crushed into an infinitely small space.
“Black holes are the X-games of physics. They represent an unexplored extreme of space-time,” said astrophysicist Adam Frank.
Because black holes by definition don’t emit any light, it is actually impossible to photograph one. However, it is possible to observe the gases and other matter orbiting the black hole. This matter, called the event horizon, orbits the black hole at such high speeds that it is heated up to the point where it emits electromagnetic radiation. These heat, light, and radio waves are what scientists can detect and study.
After more than a decade of work, scientists used a network of eight radio telescopes around the world to create, “a virtual telescope dish as large as the Earth itself,” said the National Science Foundation. The Earth’s rotation allowed the telescopes to fill in empty spaces and create a complete picture. Additionally, each signal received by the telescopes had to be synchronized using atomic clocks and a supercomputer, and it took many hours to record enough data to produce a single image.
In the new image of the black hole, there is a ring of light with a shadow in the middle. The ring of light is the event horizon, and the shadow in the middle indicates where the gravity is so strong near the black hole that the electromagnetic radiation cannot escape it. This shadowy area is approximately 2.5 times the size of the black hole itself.
Because the researchers at the EHT project measured radio waves to produce their image, the colors aren’t representative of what would be seen with the naked eye. However, the colors do tell us that the black hole is spinning. The lower half of the ring is brighter because it is spinning towards Earth, and the upper half dimmer because it spins away.
Einstein first hypothesized the existence of black holes over a century ago, and scientists have indirectly studied black holes for decades; from observing how they affect nearby stars and giant clouds of gas, to determining how they send ripples through space and time.
“You have probably seen many, many images of black holes before,” said Heino Falcke, a professor in the Netherlands who chairs the EHT Science Council. “But they were all simulations or animations. And this [image] is precious to all of us, because this one is finally real.”
Shep Doeleman, the Harvard University astronomer who lead the EHT project, says that the detail of the images should increase dramatically as more radio telescopes join the project. He even hopes that researchers will be able to make a movie of the black hole in action in the near future.
Because the black hole is so large, it takes a long time for the matter making up the event horizon to orbit it. This means that the EHT project could create multiple images like the one just released, and make a movie one frame at a time.
“The time scale over which [the black hole] changes appreciably is greater than a day. That’s great,” said Doeleman. “…if we want to make another [image], or a time-lapse movie, then we just go out the next day or the next week. And we might do it seven weeks in a row and get seven frames of a movie and then kind of see something move around in that way.”
These movies could reveal new information about the behavior of gravitational fields surrounding black holes, and change the way we understand the universe forever.