Black holes are fascinating and bewildering objects. On the occasion of the fifth Black Hole Week 2024, NASA engineers invite us to plunge into the heart of one of them. A supermassive black hole like the one hiding at the center of our Milky Way. An unparalleled experience.
What would happen if you fell into a black hole? You have probably asked yourself this question before. And NASA has decided to provide you with an answer. A challenge even for astrophysicists. But a way for them, by simulating difficult to imagine processes, to practice connecting the complex mathematics of relativity to their real-world consequences.
A Supercomputer to Simulate a Supermassive Black Hole
Thanks to the capabilities of NASA’s Discover supercomputer at the Center for Climate Simulation, engineers have managed to reveal what happens at the center of a black hole. Their project generated about 10 terabytes of data over approximately 5 days. A conventional computer would have taken more than a decade. To do what exactly? To simulate a camera – but the result would be the same for a daring astronaut – crossing the event horizon of a black hole.
To make the experience more spectacular, researchers chose a supermassive black hole. 4.3 million times the mass of our Sun. A black hole similar to the one lurking at the center of the Milky Way. Smaller black holes, a few tens of solar masses, indeed produce stronger tidal forces that can tear apart objects approaching them before they even reach their event horizon. Astrophysicists refer to this as spaghettification.
The Tragic Fate of a Camera Falling into a Black Hole
The simulated black hole’s event horizon spans about 25 million kilometers. Just over 15% of the distance between Earth and the Sun. A flat, swirling cloud of hot, glowing gas.
An incandescent accretion disk surrounds and serves as a visual reference during the fall towards the black hole. The luminous structures called photon rings, which form closer to the black hole from the light that has orbited around it one or more times, have a similar role. A starry sky seen from Earth completes the scene.
The videos start as the camera is about 640 million kilometers away. As it approaches the black hole, the camera accelerates at speeds closer and closer to that of light. Similar to the sound of an approaching race car, the glow of the accretion disk and stars in the background amplifies. Everything distorts more and more, giving rise to multiple images as their light travels through increasingly warped spacetime.
In real-time, the camera takes about three hours to reach the event horizon. It completes nearly two full orbits along the way. However, to an observer from afar, the camera would never reach the event horizon. As spacetime bends, the camera’s image would slow down and appear to freeze just before. This is why astronomers initially referred to black holes as “frozen stars.”
Once the event horizon is reached, even spacetime flows inward at the speed of light. Subsequently, the camera and the spacetime in which it moves rush towards the center of the black hole—a one-dimensional point called singularity, where the known laws of physics cease to operate. The camera’s destruction by spaghettification then takes no more than 12.8 seconds. It only has 128,000 kilometers to go in the blink of an eye until the…A scenario proposed by NASA engineers suggests that if a camera narrowly misses the event horizon of a black hole, time would not flow the same way. Physicists explain that if an astronaut accompanied the camera and then returned to the mothership, which stayed safely away from the black hole, they would be 36 minutes younger than their colleagues. This is because time passes more slowly near a strong gravitational source and when traveling at speeds close to that of light. If the experiment were repeated with a rapidly spinning black hole like in the movie “Interstellar,” the bold astronaut could potentially return several years younger than those who stayed behind.