How Do Stars Form?

Stars come from humble beginnings. They form due to a build up of gas and dust in the galaxy.

Gravity causes this build up to collapse and a star to form. Star formation can take millions of years from when the gas cloud begins to collapse.

Stars, just like the sun, have not always been there. They are born and then die across millions of years. Stars are born when large areas of gas and dust in space collapse as a result of gravity. These conditions can be referred to as star nurseries.

Star Nurseries

Huge areas of dust and gas are present in spaces between stars. These spaces are called interstellar mediums.  The accumulations of gas and dust are referred to as molecular clouds, which are located inside interstellar mediums.

Molecular clouds are formed from an accumulation of dust, atoms, molecules. Atoms are the building blocks of every object, and molecules are two or more atoms bonded together. Molecular hydrogen (H2) is the main molecule present in molecular clouds, but more complex molecules, such as methanol and water can also be present. 

Dust is made from large chunks of matter and can be a few millimetres in size, compared to the tiny measurements of atoms and molecules. Molecular clouds which are present in the interstellar medium are huge; thousands of times heavier than our Sun. Molecular clouds are highly varied in volume and can even be much bigger than our solar system.

Molecular clouds have turbulent motion; which means that the dust and gas move around in many directions, causing the molecules and atoms to be distributed across areas of the molecular cloud in an uneven manner. Once the dust and gas reach a high level in one area, the area begins to collapse due to its own gravity. 

The Molecular Cloud Collapse

Molecular clouds are extremely cold; a few degrees higher than absolute zero (the lowest temperature possible). However, once an area of the molecular cloud begins to collapse, the temperature rises. In physics, when matter is squashed together tightly, it’s density increases and it begins to heat up.

The inside of the collapsing area will have its temperature rise to about room temperature. Once the collapsing area of the molecular cloud has grown to a certain size, it is referred to as a pre-stellar core.

Pre-Stellar Cores

A pre-stellar core is the beginning of a star being born. The pre-stellar core is exceptionally dense, and will eventually become the interior core of the developing star.

Over many thousands of years (around 50,000) the pre-stellar core will start to contract, and the density will continue to increase while the diameter decreases to a tenth of the size of the collapsing area at the start of the collapse.

50,000 years on, the area will have created a disk around the interior core, and any leftover materials will be pushed out into space from the poles of the star.

Turbulent motion of the dust and gas alongside the area’s contraction around the core will begin a rotation of the entire area. This process creates the disk that forms around the core. The area is now a proto-star, which means it is slowly turning into a real star.


The flat disk which surrounds the pre-stellar core is very important for the proto-star to begin forming a real star. The disk is mainly gas, which rotates alongside  the disk and approaches the proto-star’s surface.

As the gas gets nearer to the proto-star, it causes a process called accretion, where mass is accumulated from another object. This is because gravity causes the gas from the disk to fall onto the surface of the proto-star, which makes the star grow larger.

As around 1000 years pass, the proto-star continues to gather more mass from the disk until a nuclear reaction is initiated, causing the star to shine. When the star shines, it can be referred to as a T-tauri star. 

T-Tauri Stars

The T-tauri star is the first time a developing star can be observed visually during it’s growth. Once the star has finished taking matter from the disk, the disk is no longer required to grow the star. The disk is now a circular mass of materials which clump together and orbit the star. 

The Formation Of Solar Systems

The small clumps of material will later form new planets, which points to the fact that our solar system contains planets formed through the leftover materials created during our Sun’s formation.

A solar system has been created once all of the material from the disk has been used up and all the planets have been created. The next 10 billion years will see the new-born star burn through the nuclear fuel from its core in order to emit energy as sunlight radiation. 

How Can We Find Out If A Star Is Being Born?

Molecular clouds that create stars are dark areas in the sky which are impossible for humans to see, even with a telescope. This is because the dust particles which are all over the cloud absorb light from the stars around the area, which prevents light from reaching the Earth. This is why molecular clouds just look like big, dark areas in the night sky.

However, molecular clouds are transparent to radio waves, because they are not absorbed by dust particles. This means that they can reach us on Earth. Astronomers can therefore use radio telescopes to receive signals from molecular clouds.

When a star is being formed in a molecular cloud, the molecular clouds will send out distinct radio waves which are different from when no star is being formed; allowing astronomers to detect whether a new star is being born. 

Final Thoughts 

There are still many mysteries surrounding the stars and our universe. Although astronomers already know that stars about six times greater in mass then our own Sun are formed in the same way the article describes, even larger stars exist which are born of a different process.

Hopefully, future astronomy endeavours will shed some light on the many great mysteries of star formation and the wonders of space as a whole.

Gordon Watts