This book explains how stars are born, describes the different types of stars and their color and brightness, and traces their evolution into giants, white dwarfs, neutron stars, and black holes. The color of a star is related to its surface temperature, which can be used to estimate its condition and age. Humanity’s dreams of space and how the study of stars can lead to future space exploration are also discussed.
It’s hard to see them nowadays, but when you leave the city and look at the sky at night in the mountains or in the countryside, the shining stars are very beautiful. You’ve probably thought about them at least once while looking at such a landscape. What are stars? Few people know how stars are born, and even fewer know what they’re talking about, so I thought I’d take this opportunity to explain the birth of stars, the types of stars, their brightness and colors, and more.
First, the birth of a star. Stars are born in a dense region of interstellar matter called the nebula, which is 98% hydrogen and helium gas and 2% dust. This dense nebula slowly contracts under its own gravity, which increases the density and temperature of the center of the nebula. When it starts to glow on its own, it’s called a proto-star. When the temperature of the core of the proto-star reaches 10 million K, hydrogen fusion reactions begin to take place there, at which point the gravitational contraction of the star stops and we call it a ‘star’. Stars of this age are called main sequence stars. The main sequence is the stage of a star’s life, and our familiar Sun is an example of a main sequence star.
So what are the different types of stars? Unlike planets, stars are celestial objects that produce their own light, and the stars we usually think of are “sidereals” like the Sun. This sidereal includes only the Sun in our solar system, but there are many sidereals throughout the universe. There are several types of stars: protostars, main sequence stars, giants, and white dwarfs.
We’ve already covered protostars and main sequence stars, now let’s talk about giants. A giant star evolves past the main sequence stage when the main sequence star finishes its hydrogen fusion reactions. If the star’s mass was less than 0.4 times the mass of the Sun when it was a main sequence star, it will be a red giant. If it is more, it will evolve into a yellow or blue giant. However, some stars with an initial mass less than 0.25 times that of the Sun never reach the giant stage and evolve directly into a white dwarf. A white dwarf is the final stage that most stars reach. If a white dwarf exceeds 1.4 times the mass of the Sun, it becomes a neutron star, and if it is more than three times as massive, it forms a black hole. However, white dwarfs are typically about half the mass of the Sun, so many stars end up in the white dwarf state without evolving further.
White dwarfs stop fusing when hydrogen fusion is complete, helium fusion is complete, and nuclear fusion stops because they can no longer reach high temperatures. This leaves only a core of carbon and oxygen, making it a cold star that no longer produces energy. White dwarfs are the most common type of star we can see in the sky, which makes them the easiest objects to find in the universe.
Stars undergo a variety of changes from birth to death, and their evolution is an important topic of astronomical research. The birth and evolution of stars is essential to our understanding of the universe, and the various elements they produce eventually contribute to the formation of planets and life.
Now let’s talk about the brightness and color of stars. The brightness of a star is divided into two categories: apparent magnitude and absolute magnitude. Apparent magnitude literally means the brightness of the star as seen by our eyes, which is how bright the star appears when observed from Earth. The absolute magnitude, on the other hand, is the brightness of the star when it is 10 parsecs (32.6 light-years) away from Earth, and is used to compare the actual brightness of the star itself. This allows us to determine the true brightness of a star by comparing its apparent and absolute magnitudes.
The brightness of stars is categorized into magnitudes, starting with magnitude 1 and getting dimmer as the number increases. Interestingly, magnitude 1 is not the brightest. In fact, there are zero and negative magnitudes as well, and these magnitude differences give a clearer picture of the difference in brightness of a star. For example, stars of magnitude 1 and 2 have a brightness difference of 2.512 times, and a magnitude 5 difference is about 100 times brighter. Comparing the brightness of stars in this way is an important way for astronomers to understand the physical properties of stars.
Next is the color of the star. A star’s color is an indication of its surface temperature, which can be determined from the spectrum of light it emits. The color of a star depends on its surface temperature, with hotter stars being bluer and cooler stars being redder. The colors of stars are divided into seven categories: O, B, A, F, G, K, and M. The Sun is a type G star, a yellow star with a surface temperature of about 5,500°C. This allows us to understand the color and temperature of a star, as well as the stage of its evolution.
For example, a blue-colored O-type star has a very high surface temperature and is likely a young star. Conversely, a reddish M-type star has a lower surface temperature and is more likely to be in a later stage of evolution. In this way, the color of a star is not just a decorative element, but an important clue to its state and evolution.
So far, we’ve covered the birth of stars, types of stars, and their brightness and color. To recap, stars are born in nebulae, become protostars, and then main sequence stars. Then, depending on its mass, it evolves into a giant star or a white dwarf, and at the end of its evolution, it forms a neutron star or a black hole. The brightness of stars is divided into apparent and absolute magnitudes, and their color varies depending on their surface temperature. The closer to blue, the hotter the temperature, and the closer to red, the colder.
We looked at the stars and dreamed dreams, and those dreams led humanity into space. The study of stars is far from over, and their fascination still captivates us. As we continue to study them, our understanding of the universe will deepen. And in the not-too-distant future, we may even be able to travel freely through space. The universe offers us endless mysteries, and in the process of unraveling them, we will gain a greater understanding of the wider world.
