The only way we have ever really noticed a black hole was by observing the bending of light as it passed by the event horizon. But the only actual direct evidence that we have found pertaining to black holes was discovered last year when scientists detected gravitational waves.
Now scientists are getting ready to take a picture of one. There is supposedly a black hole in the center of the milky way named “Sagittarius A” and thanks to an international collaboration called the Event Horizon Telescope (EHT), scientists will be using nine radio telescopes around the world to create one large virtual telescope called the interferometry.
There is a little bit more involvement then just aligning nine telescopes into a certain direction. The Massachusetts Institute of Technology (MIT) helped develop an algorithm that combines the observational data into a mosaic, it is called a CHIRP (Continuous High-resolution Image Reconstruction using Patch priors), and it should let us directly see an image of a black hole.
Having the ability to use telescopes all around the world allows scientists a very high resolution, and having the CHIRP algorithm piece all of that data together should allow for this extreme idea to come to fruition.
“Suppose you want a high-resolution video of a baseball,” Yoav Schechner, a professor of electrical engineering at Israel’s Technion who was not involved in the paper, told MIT News. “The nature of ballistic trajectory is prior knowledge about a ball’s trajectory. In essence, the prior knowledge constrains the sought unknowns. Hence, the exact state of the ball in space-time can be well determined using sparsely captured data.”
One of the reasons we need such a large telescope is that black holes are very far away, and also very small. For example, Sagittarius A* is just 17 times the Sun’s diameter but 25,000 light-years away.
“[Taking a picture of the black hole in the center of the Milky Way galaxy is] equivalent to taking an image of a grapefruit on the Moon, but with a radio telescope,” said MIT graduate Katie Bouman, who led the algorithm’s development, to MIT News. “To image something this small means that we would need a telescope with a 10,000-kilometer diameter, which is not practical, because the diameter of the Earth is not even 13,000 kilometers.”