By Adam England
Recently, the science community has been filled with chatter about the first ever image of a black hole. But what is a black hole? And if it is truly a “black hole,” how can we see it?
The idea was first conjectured in 1784 by English astronomer and clergyman John Michell, who hypothesized that a body in space with a mass much greater than the sun, yet occupying a similar sized area, may have a gravitational pull so strong that not even light could escape. It would only be detectable by its effect on orbiting bodies in its vicinity. A mind-boggling concept for his time, Michell’s theory defined light as a particle, and excitement waned when light was learned to be wavelike in the early 1800s.
The next mind to delve into the realm of super-dense gravity wells, and the potential effect on light, was Albert Einstein in 1915. His thinking opened up a “Golden Age” of black hole thought, with a slew of scientists studying these new concepts: the “event horizon” (the edge of a black hole’s gravity field beyond which not even light can escape); “gravitational lensing” (the way light curves around a strong gravitational field); and “gravitational waves” (a disturbance in space and time resulting from the interactions of such large masses). The technology to study and prove such theories, however, still had a long way to go.
Astronomers at Kitt Peak National Observatory near Tucson were the first to image gravitational lensing in 1979. In 2015, over 100 scientists from around the world partnered to measure gravitational waves at less than a ten-thousandth of the diameter of a single proton. Their results proved the first gravitational waves bending the fabric of space-time from the distant merger of two black holes. On 10 April 2019, the Event Horizon Telescope announced the first ever image of the supermassive black hole at the center of galaxy Messier 87, visually proving the concepts proposed over 200 years ago. Using a special technique called interferometry (which combines the data from many radio telescopes, located all over the earth, to simulate one giant telescope), the image shows the event horizon of a black hole.
If you would like to learn more about the sky, telescopes, or socialize with other amateur astronomers, visit our website at www.prescottastronomyclub.org or Facebook page @PrescottAstronomyClub to find the next star party, Star Talk, or event. Image courtesy of Event Horizon Telescope.