By: Davan Mulligan
Black holes, a prediction of Einstein’s theory of general relativity, are a region of spacetime where gravity is so strong that nothing can escape—not even light itself. As light cannot escape black holes, one cannot see them in the way we think of seeing. Thus the name ‘black hole’. They can only be studied by the effects they have on the things around them. Black holes form when a supermassive star dies. When a star so giant dies, it leaves behind a small and dense core. If the core is around three times the mass of the sun or bigger, it will collapse in on itself to form a black hole.
The Event Horizon
The event horizon is the point at which the gravitational force of the black hole becomes so strong that light cannot escape it. Past this point, we cannot see what happens. The event horizon is the “point of no return,” because to escape it, one would have to travel faster than the speed of light. Imagine you were watching someone fall into a black hole. When they reached the event horizon, you would not see them fall further into the black hole; they would simply fade away and disappear.
In the centre of a black hole, there is a gravitational singularity. The gravitational singularity is where gravity is so intense it curves spacetime itself. It is a one-dimensional, infinitely small point that contains great mass. In this point, gravity and density become infinite and spacetime curves forever. It is at this point that the laws of physics as we know it dissipate.
Over 50 million light-years away lies Messier 87 (M87), a galaxy in the constellation Virgo that contains a colossal black hole. In 2019, scientists took the first-ever image of a black hole, the M87 black hole. M87 has a mass 6.5 billion times the mass of the sun, yet is only 40 billion kilometres wide. That’s about four times the diameter of Neptune’s solar orbit. As one cannot actually see a black hole, the image is of its “shadow,” the matter around it. Taking this “shadow” image involved eight radio telescopes on the ground around the globe, working together as if they were one single telescope the size of the Earth.