In our daily work and life, we are often asked, "Where are you from?" How should we answer? Which province, which city, which county, which district? We are Chinese and Asian! If you look at the problem from another angle, then you will say "I am from the earth".
The Milky Way is our home with 400 billion stars. On a clear night, people can see the dense belt of stars stretching across the sky, giving the Milky Way its name. From an observation point with a good viewing angle, we can look up at the Milky Way, but if we step out of the Milky Way, we can see its entirety. From that perspective, the Milky Way looks like an island surrounded by endless darkness.
Milky Way Nebula
From our perspective, the Milky Way seems to be an isolated island in the universe, because the nearest galaxy to the Milky Way is 2 million light-years away from us. So we seem to be floating alone in a sea of endless darkness. The Milky Way is extremely huge to us, so in reality humans do not yet have realistic and feasible technology to allow us to leave this huge island.
How was the Milky Way born? How did it evolve into the galaxy we are now in? How will it end in the future? We play our role in the Milky Way. The Earth we live on is located within the Milky Way. The Earth orbits a small star called the Sun.
In reality, we cannot leave the Milky Way to observe this world. But science allows us to leave the Milky Way in our imagination and observe the Milky Way from a different perspective of time and space. Ideal scenes like this are often used in our modern science fiction films.
The European Space Agency launched a space probe named "Gaia" (named after the ancient Greek goddess Gaia, which means the ancestor of life on earth) in December 2013. Its mission is to map the Milky Way. Star map of billions of stars. It is launched and entered into an orbit 1.5 million kilometers away from the earth. It can scan the entire Milky Way. It calculates the speed and direction of each star and accurately locates the position of each star with an accuracy of one hundred thousandth of an arc second. . It scans more than 1.5 million stars every hour, and it has scanned about 2 billion stars in total, which is an unprecedented achievement.
The Gaia space probe measured the speed and position of stars. In this way, their trajectory can be known to predict the future of the Milky Way. In addition, Gaia can calculate their past positions and the past appearance of the Milky Way. The history of each star can be traced by calculating its proper motion. The Gaia probe pioneered a new science - galactic archeology. (Origin of the Milky Way)
The Milky Way taken by Gaia
The earliest galaxies appeared hundreds of millions of years after the Big Bang. Large spaces formed between gaseous nebulae. The first generation of stars was born at the junction of filamentous dark matter , where the gas density is extremely high and will eventually collapse under its own gravity, triggering fusion and igniting stars. In that space, billions of new stars gather close to each other, including the still-gestating Milky Way.
1 When the Milky Way was formed in the universe 2 billion years ago, there were dozens of galaxies distributed near the Milky Way. Together with the Milky Way, they formed the Starlight Islands. Six billion years before Earth was formed, some stars in the Milky Way already had their own planets.
Over time, interstellar gas increased the rate at which new stars were produced in the Milky Way. Long before the sun was born. An era in which the galaxy Gaia-Enceladus collided with the Milky Way has come to an end. What contributed to the formation of the sun?
At the edge of the distant Milky Way, the Gaia detector investigated an extremely large celestial structure. This is a stream of stars rotating around the Milky Way. It is extremely huge. Whenever we look up at the sky at night, the stars visible to the naked eye are roughly within a few thousand light-years. Imagine that the light we see now is from those distant stars that were emitted from the Shang Dynasty, and it took thousands of years to reach us.
When the Sagittarius dwarf elliptical galaxy passed through the Milky Way, it brought new gas and new energy. The galactic collision sent ripples through the Milky Way's interior. It ushered in a magnificent era of star birth. In the outer reaches of the Milky Way, the Sun was born at this moment, and soon the Earth appeared in the Solar System. Together they embarked on a journey across the galaxy. (The sun is not stationary, but we don’t notice it moving.) Solar system objects were born in the Milky Way, and their birth benefited from an intergalactic collision. After the collision, the remnants of the Sagittarius dwarf elliptical galaxy are still orbiting outside the Milky Way. In five billion years, this galaxy has passed through the orbit of the Milky Way twice. Each encounter between galaxies will trigger the emergence of a new batch of stars.
In fact, no galaxy is a real island. The history of the Milky Way can be traced back to 13 billion years ago, and it may even be a galaxy that appeared not long after the Big Bang. The Milky Way is a history of collisions and interactions between galaxies. Flows of large and small stars stir the void, which also triggers the formation of planetary worlds like the Earth. The origins of each of us can be traced back to the collision between galaxies. We may be small, but we are all the product of major events in the universe.
The planet we live on orbits a star, and extraordinary events have occurred here. The Milky Way has shaped us but does not exist because of us. We are merely accidental by-products of unexpected events in the course of the Milky Way's history.
