The Milky Way is the galaxy in which we live, one of the numerous stars and dust in the universe. This is a common sense that most people know, and everyone learned it when they were in elementary school.
But 100 years ago, the nature of the galaxy, and the universe itself, was still a subject of much debate. On April 26, 1920, the National Academy of Sciences of the United States held a world-famous “Astronomy Debate of the Century”. Both sides of the debate are famous: one is Herb Curtis, who believes that the “Andromeda Nebula” is located outside the Milky Way, and the other is Harlow Shapley, who believes that the Nebula is located in the Milky Way.
It was Edwin Hubble who ended this argument and revealed the mystery of the Vortex Nebula. With the help of a telescope, Hubble took pictures of a number of vortex nebulae, which can help people establish a “measurement ruler” between the Milky Way and the galaxy beyond the galactic, and calculated that the distance between the two nebulae and the Earth is 900,000 light years. At the time, the known Milky Way galaxy was only 100,000 light years in diameter, which undoubtedly shattered Shapley’s view of the universe.
This discovery was announced at a meeting jointly convened by the American Astronomical Society and the American Association for the Advancement of Science in 1925.
For many years, the size of the Milky Way has been relatively easy to remember: the thickness is about 1,000 light-years and the width is 100,000 light-years. But a 2015 study showed that our Milky Way may actually be at least 150,000 light-years wide. This vast area has approximately 680 billion times the mass of the sun.
The Milky Way has 100 to 400 billion stars, and each star may be accompanied by more than one planet on average, which means that we may have more than 400 billion exoplanet neighbors.
The Milky Way has a history of 13 billion years. It is one of the 50 galaxies in a local galaxy cluster, and the local galaxy cluster itself is a part of the local supercluster. Only the Triangulum and Andromeda galaxies are close to our galaxies; the rest are much smaller dwarf galaxies. After about 4 billion years, the Milky Way will become larger. This is because Andromeda, 2.5 million light years away, is colliding with us. These two galaxies will merge to form the so-called Milky Way Andromeda.
Looking up at the starry sky on a clear night without light pollution, the Milky Way is like a hazy belt of light. The ancient Greeks believed that this phenomenon was caused by the sacred milk splash. In Greek mythology, the milk of the queen Hera has magical powers and can live forever after eating. One day, while Hera was asleep, Zeus hugged Hera Kles, born of his union with a mortal, to Hera’s side and let him suck Hera’s milk. Unexpectedly, Hera Klers awakened Hera when she sucked too hard. Hera jerked the child away, but the milk splashed into the sky and formed the Milky Way. In English, people also use the “Milk Road” to mean the Milky Way.
Side of the Milky Way
Imagination of the collision between the Milky Way and Andromeda
It is not easy for astronomers on Earth to figure out what the Milky Way looks like from the outside. But scientists have drawn a very reasonable picture by plotting the distribution of stars in a galaxy and comparing these data with the shapes of other galaxies.
Central spiral bar: Some spiral galaxies, like our galaxies, have a thick spiral bar covered with stars and dust running through the center; it is usually a sign of an older galaxy.
Galactic Center: Like most galaxies, there is a supermassive black hole in the center of the Milky Way. It is named Sagittarius A, and its weight is equal to 4 million suns.
Arms: protruding arms. Our galaxy has two—Perseus and Sagittarius, as well as some weaker arms, which are mainly caused by the uneven distribution of stars.
Us: Our solar system is located on the arms of Orion, and the distance to the center of the Milky Way is about 26,000 light years.
Disk: Most of the stars, gas, and dust in the Milky Way are on this plane. Protruding part: The protruding part in the center of the silver plate that is approximately spherical is called the core ball. There is a small dense area in the center of the nuclear ball, called the silver core.
Silver halo: There is a huge collection of spherical hot gas around the flat disk surrounding our galaxy, which rotates in the same direction as the arm of the galaxy.