The universe is in motion, and "turning" is one of the most common ways of moving in the universe.
Our solar system is rotating, and the core factor that causes the solar system to rotate is the sun. The Sun's ability to dominate the motion of the Solar System is a matter of course, as the Sun accounts for 99.86 percent of the solar system's total material, meaning that eight planets, including Earth, the moons of 173 planets, including the Moon, a large number of dwarf planets, tens of thousands of asteroids, and other celestial bodies together account for only 0.14 percent of the solar system's total mass. In contrast, the sun's power is too strong, so it can naturally dominate the rotation of these tens of thousands of celestial bodies. However, the sun is not the center of the universe, the sun is just one of hundreds of billions of stars in the Milky Way, it is also in motion, it leads all the celestial bodies in the solar system to orbit the center of the Milky Way at a speed of 220 kilometers per second.
Why does the solar system orbit the center of the Milky Way? Or why does the Milky Way rotate?
The Milky Way is a huge galaxy with hundreds of billions of stars, and does such a huge galaxy center also have a celestial body with absolute mass advantage? There is indeed a powerful celestial body in the center of the Milky Way, but "having an absolute mass advantage" is not. As early as February 1974, astronomers discovered the existence of a massive object at the center of the Milky Way through light change observations and named it "Sagittarius A*," a black hole, a galaxy-level black hole. A black hole is the most powerful known object in the universe, and theoretically has a singularity of infinite density and infinite small size at the center of a black hole.
Although the size of the singularity is infinitely small, the size of the black hole is large and small.
This is because the greater the mass of the black hole, the greater the gravitational pull, so the larger the Schwarzschild radius. Within the Schwarzschild radius, the escape velocity exceeds the speed of light because gravity is too strong, so it is completely invisible within this area. So what is the Schwarzschild radius of Sagittarius a*? Its diameter reached 48 million kilometers. 48 million kilometers, how did this data come about? Of course, it is calculated based on the mass of the black hole. So how is the mass of a black hole known? Of course, it is impossible to weigh it, but we can use the close relationship between gravity and mass to extrapolate by observing the speed of stars around the black hole. According to scientists, the mass of Sagittarius a* is equivalent to about 4.3 million suns.
4.3 million suns is indeed not small, but the Milky Way has hundreds of billions of stars, so the mass of Sagittarius a* is only about 0.0005% of the total mass of the Milky Way, of course, this is not an accurate number, because the total mass of the Milky Way can not be completely determined.
In any case, sagittarius a* this mass can not drive the entire milky way, so how did the milky way turn? Sagittarius a* does not move the entire Milky Way, but it can drive the dense group of stars around it to rotate. Through astronomical observations, scientists have discovered that at the center of the Milky Way is a bright and prominent spherical-like region with a diameter of about 20,000 light-years. There are a lot of stars in this region, and no one knows how many stars there are here, but they are obviously very dense.
The high-speed motion of these dense stars creates a gravitational core, which we now call the "silver core," and with the strong gravitational pull of the silver core, the massive Milky Way rotates.
Is the milky way spinning entirely because of the action of the silver heart? There is still controversy about this issue, because some scientists believe that the gravitational pull of the silver center, although strong, is not enough to support the entire Milky Way, you know, this is a huge galaxy with a diameter of 160,000 light years, such a huge galaxy can not be firmly held by a silver core, so they think that there may be something we can't see to provide additional gravitational action, and this invisible thing is "dark matter".
Dark matter does not belong to any kind of known matter, it is an invisible matter that exists in the universe, and may even be the main component of cosmic matter, of course, all this is only a hypothesis, a pure theory.
At present, human beings cannot determine whether dark matter really exists, but scientists hope that it exists, because the existence of dark matter will make many problems simpler and make human understanding of the laws of the universe further, but if dark matter does not exist, then many problems need to be re-recognized, such as in the absence of dark matter, why can the Milky Way be so stable, especially why is the edge of the Galaxy not out of constraints? Of course, scientists are not simply hypocritical that the stable operation of the Milky Way is related to the additional gravitational pull provided by dark matter, because the stars on the outer reaches of the Milky Way are indeed moving much faster than the theoretical values.