Black holes have been at the centre of rigorous scientific investigation for almost 200 years. However, the way black holes have been portrayed in science fiction has led to some strange misconceptions about how these heavenly chasms actually work. Dispelling these popular myths was the subject of “Black Holes Don’t Suck,” a talk hosted by the Graduate Astronomy Students’ Association on November 5, as part of their monthly public tour of U of T’s Department of Astronomy and Astrophysics. The talk was given by Nick Tacik, a graduate student in the department, whose current research involves simulating binary black holes using computers.
“As someone who studies black holes, it actually kind of bothers me a little how they are portrayed in popular culture — in particular in science fiction,” he said. “Whenever people put black holes into science fiction, it seems like the creators throw out all of the physics we know.”
The French mathematician and astronomer Simon-Pierre Laplace was the first to propose the idea of the black hole in 1796. Laplace wondered if there could be a star so dense that even light couldn’t escape from it. Albert Einstein then gave us the general theory of relativity, which is our current theory of gravity. Under general relativity, a mass, such as a star, curves the space around it.
“Now we can imagine a star with even more gravity than this one […] that it gets curved so much that if light was trying to escape from that gravity, well, the curvature would just be too powerful, and it would curve back on itself,” Tacik said.
The two essential components of a black hole are the event horizon and the singularity. The event horizon is an artificial boundary that delineates the point at which light cannot escape. The singularity is a point of infinite density at the centre of the black hole, which contains all of its mass. Black holes are formed when stars many times larger than our sun collapse in on themselves due to their large mass.
To illustrate bad black hole physics, Tacik played the audience a clip from Star Trek: Voyager. In the clip, the starship Voyager has entered a black hole. The crew says such absurd things as: “I do know one thing — that as we slide deeper into the singularity, the spatial distortions are increasing” and “If we find our entry point [in the event horizon], we may be able to slip out the way we came in.”
Why are these statements absurd?
“As we saw, the singularity is a single point. How can you slide deeper into a single point?” Tacik asked. Furthermore, “General relativity tells us that once something enters the event horizon, nothing can escape the event horizon. The event horizon isn’t actually some physical thing that you can rupture and go through.”
Tacik moved on to dispel some other misconceptions about black holes — the first on his list being that black holes don’t suck.
“Black holes have been referred to as cosmic vacuum cleaners. People think they suck up all the stars and gas and dust around them, and keep on growing and growing forever.”
This is not the case, since only objects entering the event horizon will be pulled in. For example, if our sun suddenly became a black hole, the Earth would not be pulled in, because it would be outside the event horizon.
Another misconception is that black holes are incredibly complicated.
“Black holes are very simple. You only need two pieces of information: the mass of the black hole and the spin of the black hole,” Tacik explained.
However, the most egregious error for Tacik was the concept of using black holes as time machines. In 2009’s Star Trek, Spock is thrown back into the past when his spaceship is pulled into a black hole he creates.
“You cannot use black holes as time machines. As we saw, the black hole is just the event horizon and the singularity. You go through the event horizon, you hit the singularity.” Tacik believed that maybe the scriptwriters were thinking of wormholes, which connect two different points of space and time. Although wormholes are allowed by general relativity, the means to create one do not exist. Even if you could create a wormhole, the bridge connecting the two points would collapse before you could go through it.
The final misconception that Tacik addressed was that the Large Hadron Collider, a particle accelerator in Switzerland, would destroy the Earth. The LHC can create mini black holes, causing some to fear that one will be created that will end our existence as we know it. However, as Tacik outlined, thanks to Hawking radiation — which causes black holes to radiate energy by pulling one part of a particle/anti-particle pair into the event horizon — these mini black holes evaporate once they are created.
“[Regular black holes] radiate very, very slowly and we’ll probably never be able to observe it. […] But if you had a very small black hole, like we might at the LHC, [which combines] two protons and makes them into a black hole, then these mini black holes evaporate very, very quickly. It’s a very short amount of time.”
Ending the evening on a light note, Tacik played the audience a clip from Futurama, in which Fry comforts a sulking Bender after his girlfriend falls into a black hole.
“Don’t cry, Bender. Nobody really knows what happens in a black hole. It’s possible she’s still alive in another dimension somewhere, right Professor?” Fry says.
“Oh, absolutely,” the Professor assures him, before turning to whisper: “Not a chance.”
Top four myths about Black holes
Black holes are vacuums
Black holes are not “cosmic vacuum cleaners” that suck up all the matter, dust, and gas around them to grow bigger and bigger. Only objects that enter the event horizon are pulled in. Everything outside the event horizon remains outside the black hole.
Black holes are time machines
Nothing can go further into the singularity once it reaches it. Spock, and anyone else that entered a black hole, would be no more.
The LHC WILL destroy the Earth
The mini black holes created by the LHC evaporate as soon as they are created. They are practically non-existent.
Black Holes Are Complicated
Black holes are actually really easy to understand and even simpler to describe than the Earth itself. There are only two pieces of information that you need: the mass and the spin.
