Without a doubt, black holes are among the most mysterious types of objects in the universe. Scientists understood their existence in the early 20th century in the wake of Albert Einstein’s revolutionary proposals on gravity. It wasn’t until 1964 that scientists even claimed to have observed one, and it wasn’t until 2019 that astronomers were able to release the now-famous photo of the supermassive black hole at the center of the Milky Way galaxy M87, the first real image of a black hole.
That said, Christopher Nolan’s blockbuster ‘Interstellar’, which clearly features a black hole, was released in 2014. So even if he prefers to avoid CGI, Nolan had no choice but to use computers to create the film’s black hole. And he could only do that because there has been a long tradition of generating images of a black hole since 1979.
The universe, it turns out, likes to follow rules. The entire history of physics – really, just the whole of science – can be summed up in one sentence: the quest to find out what the rules of the universe are. Scientists define these rules using mathematical equations. All it took to create an image of a black hole was plugging those equations into a computer and having it spit out a result. How hard can it be? Incredibly difficult, as it turns out, because the first problem was figuring out the equations in the first place.
For a long time, scientists have understood gravity as formulated by Isaac Newton in 1687: every object in the universe exerts a force on every other object in the universe, and that force is proportional to the product of the objects’ masses (how great is gravity?) there is a lot of stuff) and inversely proportional to the square of the distance between the centers of the objects. In simpler terms, larger objects and shorter distances produce more gravity.
And then Einstein came along and made everything a lot more complicated. It turns out that there were a few cases where Newton’s theory of gravity didn’t perfectly predict what was going on. Although Newton was able to describe the force created by gravity, he was never able to determine what created that force. He gave us the ‘what’, but not the ‘how’ and ‘why’. Einstein’s theories built on the work of Newton and other physicists to fill that gap, solving some of the cases where Newton’s theory failed.
In 1905, Einstein unveiled his special theory of relativity, which was based on two ideas: first, that the laws of physics never change as long as you move at a constant speed, and second, that the speed of light in a vacuum is always equal to the speed of light. the same no matter what. If you’ve ever heard of ‘spacetime’ or the ‘space-time continuum’, this is where it comes from. In order for the speed of light to always remain the same, time and distance must both change, sometimes in unexpected ways (famously: time dilation). This strange, counterintuitive connection between physical space and the passage of time is a crucial part of the way our universe works.
For the next ten years, Einstein worked to find out if he could fit gravity into his theory of spacetime, and that’s what general relativity did. To oversimplify, every object in the universe physically warps the field of spacetime, changing the trajectory of any object that comes close to it. According to Einstein’s theory, we regard that change in trajectory as gravity, and nothing, not even light, is immune.
Not long after, some physicists, such as Karl Schwarzschild, noticed a potential problem: what if an object had such a large mass that it could warp spacetime so much that even light, the fastest object in the universe, could not escape? Well, when light is absorbed into something, our eyes perceive that object as black. And this black object would have to be absurdly dense, so dense that at its center it might appear as if it had created a tiny hole in the fabric of spacetime.
In other words – wait a minute, the exact same words actually – a black hole.
Scientists have since built on these theories, confirming that Einstein, Schwarzschild, and others were right time and time again. However, trying to explain the concept to the public is a completely different matter. In general, people like to know what something looks like, and the rules of a black hole make answering that question very difficult.
But in 1979, French cosmologist Jean-Pierre Luminet discovered a way to do this using the theories and equations that dictate how gravity pulls objects like outer space into a black hole (it’s quite a messy process, as it turns out) . Contrary to the public perception that a black hole is just a giant galactic vacuum cleaner, a black hole simply exerts gravity, no more, no less. And gravity, in case you haven’t picked up on it yet, is very complicated.
So when Luminet created his image of a black hole, he used equations to predict how the light itself would be affected as it passed close to the black hole. His result showed a small ring of light around an otherwise completely black circle. He then discovered how the orbit of the space dust around the black hole could affect its image, what might happen if the black hole itself rotated, and other complications. And then he used a 1970s computer to print out a simulated photo.
In his paper, he suggested that this image, among other black holes, could accurately represent “the supermassive black hole whose existence has recently been suggested at the core of M87.”
In April 2017, a large-scale project led by Harvard astronomer Shep Doeleman scanned the sky around M87 using telescopes around the world. They then analyzed the data for two years and created a picture:
(Event Horizon telescope)
All in all, it’s safe to say that Luminet did a pretty good job.
Sources:
Brian Greene explains this whole general relativity thing. www.youtube.com, https://www.youtube.com/watch?v=0jjFjC30-4A. Accessed February 19, 2024.
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Event Horizon telescope. January 18, 2024, https://eventhorizontelescope.org/home.
First ever image of a black hole: a CNRS researcher had already simulated it in 1979 | CNRS. April 10, 2019, https://www.cnrs.fr/en/press/first-ever-image-black-hole-cnrs-researcher-had-simulated-it-early-1979.
First image of a black hole – NASA Science. https://science.nasa.gov/resource/first-image-of-a-black-hole/. Accessed February 19, 2024.
“How building a black hole for ‘Interstellar’ led to an astonishing scientific discovery.” Wired. www.wired.com, https://www.wired.com/2014/10/astrophysics-interstellar-black-hole/. Accessed February 19, 2024.
Imagine the universe! https://imagine.gsfc.nasa.gov/features/yba/CygX1_mass/cygX1_more.html. Accessed February 19, 2024.
Interstellar 4K HDR IMAX | In the black hole – Gargantua 1/2. www.youtube.com, https://www.youtube.com/watch?v=OA3Txp94pjs. Accessed February 19, 2024.
Luminet, JP “Image of a spherical black hole with thin accretion disk.” Astronomy and astrophysics, full. 75, May 1979, pp. 228–35. NASA ADShttps://ui.adsabs.harvard.edu/abs/1979A&A….75..228L.
Press release (April 10, 2019): Astronomers capture first image of a black hole. https://eventhorizontelescope.org/press-release-april-10-2019-astronomers-capture-first-image-black-hole. Accessed February 19, 2024.
Special Relativity: Crash Course in Physics #42. www.youtube.com, https://www.youtube.com/watch?v=AInCqm5nCzw. Accessed February 19, 2024.