Today, most people have heard of black holes. But many enthusiasts don’t know exactly what these strange objects are and what they are capable of. Part of the reason is that his name is a bit inaccurate. A black hole is not just an empty hole in space, but an entity in the universe with a very large mass. (Mass is a measure of the amount of matter in an object.) A black hole has a hole or tunnel structure; but it is not empty, it has physical properties, things that can be measured with human instruments.
For example, the large mass of a black hole creates a vast gravitational field that scientists can detect. Gravity is the force of all matter that brings objects together. For small objects such as molecules, pebbles, people, houses, and even all four, gravity is too weak for human senses to perceive or instruments to measure; Only on planets or larger is gravity clear and measurable. For example, the Earth’s gravity keeps the Moon orbiting around it, and the gravity of the Sun, the star at the center of our solar system, keeps Earth and the other planets orbiting around it. Similarly, a black hole exerts a gravitational pull that pulls objects toward it when they get too close. “In fact,” writes astronomer Thomas T. Arny,
The gravitational field produced by a black hole is no different from that of other objects of the same mass. For example, if the Sun suddenly turns into a black hole with the mass it has [điều này không thể xảy ra]the Earth will still revolve around it as it does now.6
“Creation of attraction”
Black holes not only create enormous gravitational pull, but they also have a process that uses gravity to compress a large amount of matter into a very small space. This makes them extremely heavy or extremely dense objects. Extremely massive and massive objects have a much larger mass than ordinary planets and stars, which have smaller masses. In fact, a black hole’s gravitational pull is so great that it can trap even light, nature’s fastest-moving matter. This is why black holes are black: no light escapes for the human eye or telescope to see their shape.
Based on the relationship between black holes and gravity, black holes can be called “gravity creatures”. Because it is impossible to study black holes without knowing how gravity works, especially in such extreme cases. In fact, it took many years of careful study of how gravity works for scientists to first determine the existence of black holes, even though at the time they weren’t called black holes and there is not a single piece of evidence to prove their existence. .
Discovery of the gravity of the universe
The first theory of gravity appeared in 1666. Before that date, scientists believed that the force that held people, houses, trees, and mountains firmly to the Earth and the force that kept the Earth moving around the Sun were distinct forces. Then a brilliant Englishman named Isaac Newton pointed out that was not true; at the same time, it explains how gravity works.
According to Newton, he first got the idea of gravity when he saw an apple falling from a tree. He was of course not surprised that the apple fell and hit the ground, because he had known for a long time that there was a mysterious force that always pulled everything towards the center of the Earth. What piqued his interest was the relationship between distance and this mysterious force. He had the idea that even if he stood on the highest mountain in the world and threw an apple, it would definitely fall like from a tree branch. This means that this mysterious force is powerful enough to pull an object ten thousand feet high. This force can attract even more distant objects.
This led Newton to think of the Moon, which is hundreds of thousands of miles away from us. Maybe, he thought, the same force that makes the apple fall is pulling on the Moon. In this case, the Moon “falls” to Earth and the only reason these celestial bodies do not collide is because the Moon is constantly moving away, into space, has escaped, or is in balance. equal, this mysterious force of gravity. From this logical (and correct) point of view, it is no exaggeration to assume that the same force also causes the movement of the Earth and the other planets around the Sun. Newton concluded that this mysterious force, which he called gravity, existed throughout the universe, and was even the universe. To be appropriate, he named his new theory the law of universal gravitation.
Using a beautiful equation, Newton showed that the gravitational force between two objects depends on two factors: the mass of the objects and the distance between them. A small object with a small mass, he points out, exerts a very small force of attraction on another; A very large object with very large mass, such as the planets, will exert a measurable gravitational force on other objects. At the same time, distance also comes into play. The farther away objects are, Newton said, the weaker the gravitational pull. And the opposite is also true: the closer the objects are, the stronger the attraction. This explains why the Sun easily exerts its gravitational force on the Earth, because it is located close to this star, but the Sun’s gravitational force has no significance on other stars, because they exist at a distance of thousands of times greater than the distance from the Earth to the Sun.
Newton’s law of gravitation revolutionized physics, especially for physicists and astronomers. Science writer John Gribbin wrote:
Newton actually explained the reason why the apple falls and the motion of the Moon with one law. By this action he solved the mystery of the laws of motion of celestial bodies and opened the eyes of true scientists to the laws of planets and stars – the laws of the entire universe – which can be explained by a law of physical. a law which, from research to the laboratory, applies directly on Earth.7
Escape Velocity and Invisible Stars
One of the problems with Newton’s law of gravitation is that it inevitably leads to the fundamental concept of what we today call a black hole. While researching gravity, some of his immediate successes highlighted the conditions for escaping gravity. Newton’s equation shows why the Earth moves around the Sun without falling into it; More precisely, the planet is moving away from the Sun, but only with enough speed to balance this strong gravitational force. But what if the Earth suddenly accelerated, some scientists wondered? Logically, it would free itself from the gravity of the Sun and free itself from the attachment of the star.
The speed an object needs to escape the gravitational pull of another object is called escape velocity. Earth’s escape velocity, for example, is about seven miles per second, meaning a rocket or spacecraft would have to reach that speed to escape Earth’s gravity. In contrast, a rocket flying at seven miles per second on Jupiter would not be able to escape the planet. The reason is that Jupiter is much heavier than Earth and therefore its gravity is much greater. “The escape speeds of different worlds are different,” explains the famous science writer Issac Amov.
A world lighter than Earth… has a lower surface escape velocity…. On the other hand, worlds heavier than Earth will have higher escape velocities. It is not surprising that in the planetary system Jupiter has the highest escape velocity… On the surface of Jupiter, the escape velocity is 5.4 times higher than the escape velocity on the surface of the Earth.8
During the 1700s, several scientists thought extensively about the idea that objects with greater mass would have greater escape velocity. One of these researchers was the British astronomer John Michell, who carefully studied the properties of stars. Apparently there are many stars in the sky that are more massive than the Sun. Michell doesn’t know if there is an upper limit to the size of stars. But at least in theory, he proposes, there are stars with enormous masses, and as such their gravitational pull would be enormous. In addition, the escape speed of such massive stars will therefore be very high.