In the past few years, black holes have often made headlines in many science and technology pages. In 2019, the appropriate event horizon telescope (EHT) successfully photographed a black hole for the first time. In may2022, eht took a picture of Sagittarius a* which is a supermassive black hole in the center of the Milky Way galaxy.
Due to the endless stream of science fiction and film works, most people think of these black holes as the bullies of the galaxy, wandering in the universe and devouring anything that hinders them. But black holes are invisible. When you approach a black hole, they slow down time and obviously don't work like a vacuum cleaner, sucking away everything it thinks is space dust.
The reason is very simple. Like the earth and other masses in the universe, black holes also have their own gravity. Planets can orbit black holes, just as the earth orbit the sun and the moon orbit the earth. In fact, Dr Christina Smith, who holds a Ph.D. in Astrophysics from the University of Manchester, points out that if the sun suddenly disappears and a black hole (with exactly the same mass) replaces its position, the earth page will not be sucked in; It will continue to run around it as if nothing had happened.
Furthermore, if the earth is replaced by a black hole with the same mass, the black hole will not fill the same volume. It can only create a space volume occupying only two centimeters in diameter, that is, a black ball called the event horizon. The event horizon is a theoretical point of no return around the black hole, where absolutely nothing -- including light -- can break away. The black hole is the most dense object known in the whole universe. However, the "curvature of space" around the black hole will be the same, so objects passing through the earth may miss the black hole. More importantly, objects that originally hit our planet may avoid the black hole completely in this case, because they must cross the small two centimeter event horizon to be trapped.
Mass is the key to this phenomenon. At the center of each black hole, there is a singularity -- a tiny region with an infinite mass concentration. We know that the gravity of an object increases exponentially according to the mass of the object. As long as an object remains outside the event horizon, it may escape the huge gravity of the black hole, but the closer it gets, the faster it needs to move away. Once it crosses the event horizon The story has no good ending.