On Halloween, ghosts, goblins and ghouls haunt, but nothing in the universe is more terrifying than a black hole.
Black holes—a region of space whose gravity is so strong that they cannot escape—have become a hot topic in today’s news. Half of the 2020 Nobel Prize in Physics is awarded to Roger Penrose, because his mathematical work shows that black holes are an inevitable result of Einstein’s theory of gravity. Andrea Ghez and Reinhard Genzel shared a photo of the other half, which shows that there is a huge black hole in the center of his Milky Way.
Black holes are terrible for three reasons. If you fall into the black hole left by the death of a star, you will be shattered. Similarly, the huge black holes seen in the centers of all galaxies have an inexhaustible appetite. A black hole is where the laws of physics are eliminated.
I have been studying black holes for more than 30 years. In particular, I focus on the supermassive black hole lurking in the center of the galaxy. In most cases, they are inactive, but when they are active and eat stars and gas, the area near the black hole will be dazzling than the entire galaxy that houses them. Galaxies with active black holes are called quasars. In the past few decades, we have learned all about black holes, but there are still many mysteries to be solved.
Black hole death
When a huge star dies, a black hole is expected to form. After a star’s nuclear fuel is exhausted, its core collapses to the densest state of matter imaginable, with a density one hundred times that of an atomic nucleus. So dense, protons, neutrons and electrons are no longer discrete particles. Since black holes are dark, they will be discovered when they orbit normal stars. The properties of normal stars allow astronomers to infer the properties of their dark companion stars (black holes).
The first black hole to be confirmed is Cygnus X-1, which is the brightest X-ray source in the constellation Cygnus. Since then, about 50 black holes have been discovered in systems where normal stars orbit black holes. They are about 10 million closest examples, and are expected to spread through the Milky Way.
A black hole is a tomb of matter. Nothing can escape them, not even light. The fate of those who fall into the black hole will be a painful “Italization,” which is a popular idea by Stephen Hawking in his “A Brief History of Time.” In the process of spaghettiization, the huge gravity of the black hole will pull you apart, separating your bones, muscles, bones and even molecules. Just as the poet Dante said in his poem “The Divine Comedy” at the gate of hell: Give up hope, all those who enter here.
There are hungry beasts in every galaxy
In the past 30 years, observations with the Hubble Space Telescope have shown that all galaxies have black holes in their centers. Larger galaxies have larger black holes.
Nature knows how to create black holes in huge mass ranges, from stellar corpses with masses several times the mass of the sun to monsters with masses tens of billions of times. Just like the difference between the Apple and the Great Pyramid of Giza.
Just last year, astronomers released the first ever photo of a black hole and its active horizon, a beast with a mass of 7 billion solar masses at the center of the M87 elliptical galaxy.
It is a thousand times larger than the black hole in our Milky Way, whose discoverer won this year’s Nobel Prize. These black holes are dark most of the time, but when their gravity attracts nearby stars and gas, they explode into violent activity and emit a lot of radiation. There are two dangers to a large number of black holes. If the distance is too close, the huge gravity will attract you. If they are in an active quasar phase, they will be destroyed by high-energy radiation.
How bright are quasars? Imagine hovering over a big city like Los Angeles at night. Approximately 100 million lights from cars, houses and streets in cities correspond to the stars in the Milky Way. By analogy, an active black hole is like a 1-inch-diameter light source in downtown Los Angeles, whose brightness is hundreds or thousands of times higher than that of the city. Quasars are the brightest objects in the universe.
Supermassive black holes are strange
The mass of the largest black hole discovered so far is 40 billion times the mass of the sun and 20 times the volume of the solar system. The outer planets in the solar system rotate every 250 years, while the more massive objects rotate every three months. Its outer edge moves at half the speed of light. Like all black holes, huge black holes are obscured by events. At their center is a singularity, a point in space with infinite density. We cannot understand the inside of a black hole because the laws of physics are broken. Time freezes in the event horizon, and gravity becomes infinite at the singularity.
The good news about huge black holes is that you can fall into a black hole. Despite their strong gravity, their stretching force is weaker than that with a small black hole, and will not kill you. The bad news is that the scope of the event marks the edge of the abyss. Nothing can escape from the inside of the event horizon, so you cannot escape or report your experience.[[[[There is deep knowledge every day. Subscribe to the “Talk” newsletter. ]
According to Stephen Hawking, black holes are slowly evaporating. In the distant future of the universe, with the accelerated expansion of the universe, after all stars die and the Milky Way is turned a blind eye, black holes will be the last surviving objects.
It takes years for the largest black hole to evaporate, and it is estimated to be 10 to 100 powers, or 100 zeros after 10. The most terrifying objects in the universe are almost eternal.
This article is republished from The Conversation, a non-profit news site dedicated to sharing the ideas of academic experts. Written by: Chris Impey, University of Arizona.
Chris Impey will not work for any company or organization benefiting from this article, advise it, own its shares or obtain any funds from it, and does not disclose any affiliates other than his academic appointment.