Modern Physics

Star life cycle

The life cycle of stars begins with the gathering of gases in the nebulae and lasts as long as there is fuel to be consumed in the nuclear fusion process.

 The stars are charming celestial bodies that, since antiquity, arouse people’s curiosity. But what many don’t know is that, just like us, they are born, grow and die.

The birth of a star occurs in nebulae, which are immense clouds of gas composed of Helium and Hydrogen. Due to the gravitational force, the molecules are attracted to each other, getting very close, which causes the nebula to have a reduction in size, that is, to contract. The contraction of the gases causes an increase in temperature, which increases more and more. When the temperature is high enough, this huge ball of gas starts to emit light and the hydrogen starts to burn. This process is called nuclear fusion and it releases a lot of energy. This sequence of phenomena characterizes the beginning of a star’s life.

During nuclear fusion, hydrogen atoms fuse to form helium. The burning of Helium gives rise to Lithium and so on, each time giving rise to heavier elements.

As the fuel is consumed, the temperature increases and the star expands. At this stage, she is called the Red Giant. After this stage, the gravitational force takes over and the star begins to shrink. Inside the stars, the temperature is very high. The core of the Sun, for example, reaches 15 million degrees Celsius.

How long a star will live will depend on its mass. The greater the mass, the more heat and light it will release. Its death happens when all the fuel has been burned. As this burning generates heavier elements, it ends only when it starts producing iron, which is a process that consumes energy. From then on, it cools down and drastically decreases in size, turning completely into iron.

With this contraction, the particles that were on the surface of the star go at very high speeds towards the center, when they collide with the nucleus and are ejected into space, giving rise to elements heavier than iron. The gases that are released into space give rise to a new nebula, from which new stars can emerge.

If the star’s mass is considered small, about a third of that of the Sun, it will become a neutron star. If the mass is greater, it will turn into a black hole.

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