After five days of observation in April 2017, an interdisciplinary team of astronomers, physicists and image experts were able to capture the first ever photo of a black hole.
Using a technology called synthetic aperture imaging, a group of scientist that make up the Event Horizon Telescope project was able to take an image of how the black hole is distorted by the intense gravity of itself. A black hole is a region of gravity that is so strong that light cannot escape it.
This photo, released to the public earlier this year, is significant for two reasons, said Dr. Walter Freeman, a physics and astronomy professor at Syracuse University. One is how scientists took the picture, and another is the picture itself.
“There are two pieces to it. One is that it was a demonstration of a never before used capability to take a picture of something that is that small and that far away in detail. The other is what it reveals about the object itself.”
The photo taken was not simply a picture of a black hole. The light that is seen in the photo is what comes when gas matter falls past the event horizon of a black hole, or the boundary of a black hole where no light or radiation can escape.
However, the light does not “just fly straight out,” from matter falling into the event horizon, Freeman said. Light is warped by the gravity of the black hole.
“That picture isn’t saying ‘here is where all the matter is in a black hole. It’s all of that influenced by the black holes own gravity,” Freeman said. “That picture allows us to map out the gravity near a black hole.”
The process used to take the photo, called synthetic aperture imaging, uses large telescopes placed in different observing locations around the world to capture radio waves from the black hole.
Once those radio waves are gathered, they are brought together to one point to act as “a telescope a mile wide,” said Freeman. Then, the phase, or the ups and downs of radio waves, are measured and translated into an image.
Though radio waves do not make for the best images, they must be used in synthetic aperture imaging because scientists can’t compare the phase of visible light, said Freeman.
The concept of synthetic aperture imaging has been around for a while, said Freeman. The “Very Large Array,” a version of this technology placed along train tracks in New Mexico, is a popular tourist destination built in the 1970’s.
What makes the event horizon telescope more powerful than the Very Large Array is its ability to measure shorter wavelengths. Using synthetic aperture imaging and a radio telescope that allows scientists to measure shorter wavelengths, scientists created an aperture the was “effectively a radio telescope the size of earth,” Freeman said.
“Advances in electrical engineering let us measure the phase of radio waves at higher and her frequencies,” Freeman said. “Higher frequencies, shorter wavelength, sharper picture.”
Though X-Rays are the shortest wavelength, Freeman said, they are the hardest to render into images.
A computer simulation of a black hole that was blurred out to “simulate the limited resolution of the image” looks very similar to the actual photo, Freeman said.
“What we got was the event horizon of a black hole distorted by its own gravity and then further blurred by the limited ability of the instrument to take sharp photos” Freeman said. “This is pretty remarkable confirmation that we think we understand how gravity works in extreme conditions.”
Freeman speculates that the differences between the black hole photo simulation of the real photo were partially due to the methods used to blur the simulation. Another reason, Freeman said, could have been the variation in ways that gas falls into a black hole.
“It’s like saying you can simulate a star — there are different types of stars,” Freeman said. There are different ways that this could be. The simulation may have only modeled one possibility.”
