Black Hole
A Black Hole is a mass so dense, so heavy and with such gravitational force that anything attracted to it can't escape, including light.
To imagine a Black Hole in the mind's-eye, it helps to visualize the structure of an atom. The simplest atom is common hydrogen. Hydrogen has one relatively large proton in the center (nucleus), and one electron revolving at incredible speed around the nucleus. The electron is extremely small, about 1/1836th the size of the proton. Think of a working model as looking like the Earth and it's moon. The moon represents the electron and the Earth represents the proton and the vast relative distance between the electron and the proton is similar. However, the relative sizes of the electron and proton of the model should be visualized differently: the "moon" should be visualized as the size of a basketball compared to the size of the Earth.
Said another way:
1. The protons (and neutrons) are crowded into the nucleus, an exceedingly tiny region at the center of the atom. If a hydrogen atom were up scaled to about 4 miles in diameter, its nucleus would be no larger than a tennis ball and its electron would 1836 times smaller than a tennis ball. The rest of an atom outside the nucleus is mostly empty space. The electrons whirl through this space, completing billions of trips around the nucleus each millionth of a second. The fantastic speed of the electrons makes atoms behave as if they are solid, much as the fast-moving blades of a fan prevent a pencil from being pushed through.
2. Atoms are often compared to the solar system, with the nucleus corresponding to the sun and the electrons corresponding to the planets that orbit the sun. This comparison is not completely accurate, however because unlike planets, electrons do not follow regular, orderly paths. In addition, the protons and neutrons constantly move about at random within the nucleus area.
3. The nucleus makes up nearly all the mass of an atom. Mass is the quantity of matter in an atom. Each proton has a mass roughly equal to that of 1,836 electrons. Also, it would take 1,839 electrons to equal a neutron's mass.
Considering such vast relative distances between the revolving electron and the atom's nucleus, it becomes easier to see what would happen if the electrons were stripped away. The nucleus of atoms would fit much closer together, resulting in a more compact mass without the natural separation caused by the fantastic speeds and distances of the revolving electrons.
That's what happens to create Black Holes. The enormous nuclear energy released by exploding stars forces electrons to separate from the nucleus of atoms and the weighty nuclei, attracted to each other by their own gravity, collapse onto themselves. The result is that stars become the physical size of small asteroids. (If it happened to our Sun, it would end up about 2-3 miles in diameter). Without electrons, atom remnants would no longer have the natural separation from other atom remnants. However, most of the weight remains (because almost all of the weight is in the nucleus) and so does the gravitational force. The consequence is that the nucleus blob will attract other masses that stray too near. In fact, Black Holes and galaxies, occupying the same area of the cosmos, constantly tug at one another. That's how Astronomers detect Black Holes (they can't see them because light can't escape).
Note that the gravitational force of a new black hole is no greater than the gravitational force of the star before it collapsed. The mass just becomes more compact. If our Sun collapsed and became a black hole (2-3 miles in diameter) it would still have the gravitational force necessary to hold the planets of our Solar System in their present orbits although, in reality, the gigantic explosion would destroy the planets or spin them off into outer space.
There is, however, a Critical Mass required to create and sustain the phenomenon of Black Holes just as there are Critical Masses necessary to create nuclear explosions. A collapsed dead star, large enough to create a Black Hole, would have enough gravity to pull in everything that strayed too near, including light. (Our Sun is too small to create a Black Hole. The Critical Mass needed is about ten times greater. When old Sol burns out, it will collapse as a large rock and probably eventually be sucked into a Black Hole.) Black Holes suck in everything and the crashing together of such masses results in other gigantic nuclear explosions. Most of the debris from such explosions gets sucked in causing the mass to grow even bigger and stronger. Some scientist think that eventually some black holes will grow large enough to create Little Bangs.
However, other scientist think that the whole expansion process will continue for several billion more years until the force from the Big Bang ebbs away. Then, everything will fall back together into another single blob. Then, another Big Bang will occur. Others believe that the cosmos is expanding and will continue to expand forever. We'll just have to wait and see who is right.
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