How do stars form

how do stars form in the universe

Throughout the universe we see all the stars that form the celestial vault. However, not many people know well How do stars form. You have to know that these stars have an origin and an end. Each type of star has a different formation and has characteristics according to that formation.

In this article we are going to tell you how stars are formed, what their characteristics are and their importance for the universe.

What are the stars

How do stars form

A star is an astronomical object made up of gas (mainly hydrogen and helium) and is found in equilibrium due to gravity tending to compress it and gas pressure expanding it. In the process, a star produces a lot of energy from its core, which houses a fusion reactor that can synthesize helium and other elements from hydrogen.

In these fusion reactions, mass is not completely conserved, but a small fraction is converted to energy. Since the mass of a star is huge, even the smallest, so is the amount of energy it releases every second.

Key features

star formation

The main characteristics of the stars are:

  • Mass: Highly variable, from a fraction of the mass of the Sun to supermassive stars with masses several times the mass of the Sun.
  • Temperature: is also a variable. In the photosphere, the luminous surface of a star, the temperature is in the range of 50.000-3.000 K. And in its center, the temperature reaches millions of Kelvin.
  • Color: closely related to temperature and quality. The hotter a star, the bluer its color, and conversely, the cooler it is, the redder it is.
  • Brightness: it depends on the power of the stellar radiation, normally non-uniform. The hottest and largest stars are the brightest.
  • Amplitude: its apparent brightness as seen from Earth.
  • Movement: stars have relative motion with respect to their field, as well as rotational motion.
  • Age: A star can be the age of the universe (about 13 billion years) or as young as a billion years.

How do stars form


Stars are formed by the gravitational collapse of giant clouds of gas and cosmic dust, whose densities constantly fluctuate. The main materials in these clouds are molecular hydrogen and helium, and small amounts of all the elements known on Earth.

The movement of the particles that make up the mass of mass dispersed in space is random. But sometimes the density increases slightly at a certain point, creating compression.

The pressure of the gas tends to remove this compression, but the gravitational pull that binds the molecules together is stronger because the particles are closer together, which counteracts the effect. Also, gravity will further increase the mass. When this happens, the temperature gradually increases.

Now imagine this massive condensation process with all the time available. Gravity is radial, so the resulting cloud of matter will have spherical symmetry. It's called a protostar. Also, this cloud of matter is not stationary, but rather rotates rapidly as the matter contracts.

Over time, a core will form at extremely high temperatures and enormous pressures, which will become the star's fusion reactor. This requires a critical mass, but when it does, the star reaches equilibrium and begins, so to speak, its adult life.

Stellar mass and subsequent evolution

The types of reactions that can occur in the core will depend on its initial mass and the subsequent evolution of the star. For masses less than 0,08 times the mass of the sun (about 2 x 10 30 kg), no stars will form because the core will not ignite. The object thus formed would gradually cool and condensation cease, producing a brown dwarf.

On the other hand, if the protostar is too massive, it will also not be able to reach the equilibrium necessary to become a star, so it will collapse violently.

The theory of gravitational collapse to form stars is attributed to the British astronomer and cosmologist James Jeans (1877-1946), who also developed the steady state theory of the universe. Today, this theory that matter is constantly being created has been abandoned in favor of the Big Bang theory.

star life cycle

Stars are formed thanks to the condensation process of nebulae composed of gas and cosmic dust. This process takes time. It is estimated that it occurred between 10 and 15 million years before the star reached final stability. Once the pressure of the expanding gas and the compressive force of gravity balance out, the star enters what is known as the main sequence.

Depending on its mass, the star sits on one of the lines of the Hertzplan-Russell diagram, or HR diagram for short. Here is a diagram showing various lines of stellar evolution, all of which are determined by the mass of the star.

Stellar evolution line

The main series is a roughly diagonally shaped area running through the center of the chart. There, at some point, newly formed stars enter according to their mass. The hottest, brightest, most massive stars are at the top left, while the coolest and smallest are at the bottom right.

Mass is the parameter that controls the evolution of stars, as has been said many times. In fact, very massive stars run out of fuel quickly, while small, cool stars, like red dwarfs, handle it more carefully.

To humans, red dwarfs are nearly eternal, and no known red dwarfs have died. Adjacent to main sequence stars are stars that have moved to other galaxies as a result of their evolution. In this way, giant and supergiant stars are at the top and white dwarfs at the bottom.

I hope that with this information you can learn more about how stars are formed, what their characteristics are and much more.

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