Science Alert: The year 2019 is here. With it, we’ve been promised a splendid moment in astronomy. For years, the Event Horizon Telescope has been working to bring us the first ever telescopic photograph of the event horizon of a black hole. Indeed, for all their popularity in public imagination, we have never actually seen a black hole. And the reason for that is laughably simple.
Black holes, you see, are literally invisible. The pull of their gravity is so immense that, past a certain point, nothing escapes. This includes the electromagnetic radiation – such as X-rays, infrared, light and radio waves – that would allow us to detect the object directly.
That point of no return is called the event horizon, and apart from being a terrifying location you never want to find yourself in, it’s also our key to actually visualising a black hole.
While we may not be able to see the black hole itself, there’s a chance that its event horizon can be photographed; and we are tantalisingly close to seeing the results thanks to the Event Horizon Telescope (EHT), due for a public announcement any day now.
But long before the EHT, there was an astrophysicist named Jean-Pierre Luminet. All the way back in 1978, he already gave us what could be thought of as the very first image of a black hole’s event horizon.
It’s not, of course, an actual photo. Luminet, whose background was in mathematics, used his skillset to perform the first computer simulation of what a black hole might look like to an observer, using a 1960s punch card IBM 7040 computer.
“At the time it was a very exotic subject, and most astronomers did not believe in their existence,” Luminet told ScienceAlert.
“I wanted to explore the strange physics of black holes and propose specific mechanisms that could help to get indirect signatures of their very existence. Also, to pursue the pun, with my name ‘Luminet’ I liked much the idea of how a perfectly non-luminous star can give rise to observable phenomena.”
What data the computer returned, Luminet then painstakingly plotted by hand with pen and India ink on negative paper, as if he were a human printer.
That fuzzy image – seen above – shows what a flat disc of material falling into a black hole might look like if we were close enough to see it. It doesn’t look flat, because the intense gravity of the black hole is bending light around it.
“Indeed the gravitational field curves the light rays near the black hole so much that the rear part of the disk is ‘revealed’,” Luminet explained in a paper published on arXiv last year.
“The curving of the light rays also generates a secondary image which allows us to see the other side of the accretion disc, on the opposing side of the black hole from the observer.”
Luminet was the first, but he wasn’t the only one captivated by the mystery of what a black hole might look like. Others have attempted to visualise these objects since then, and even put their efforts on the silver screen.