More help, more resources, more learning.

KidsAstronomy.com will be joining the Education.com family!

We're so excited to continue to grow and support the parents and teachers championing children's education.
Read press release
KidsKnowIt Network is now part of Education.com!

Star Formation (Star Birth)

Star formation is a simple but long process. It depends almost entirely on one thing: gravity. In outer space, things are always coming together because of gravity. As objects group-up, their gravity gets even stronger. If there’s enough matter around, it all might cluster up into a small area, creating what’s known as a protostar. This young star will then keep growing until it reaches the main sequence.

An image of Orion's nebula, where a lot of star formation takes place.

The Orion Nebula. This nebula is a site of active star formation.

The Stages of Star Formation


Cloud Collapse

Throughout the Universe, there’s a lot of well-spread out matter. Massive clouds, called nebulae, contain enormous amounts of gas. This gas, though very diffuse, is the basic material which allows for star formation. It just has to be compressed into one spot.

Several things can cause it to do so, generating a strong center of gravity. Often times, a supernova will throw matter into a nebula, pushing things together. Or, perhaps, two nebulae might come together to form a very dense cloud.

An image of a beautiful nebula. This is one of the places stars form.

Stars form within nebulae. I was wondering what was going on in there!

In any case, nebular gas begins to cluster together. As the cluster grows, its gravity gets even stronger. Eventually, it will become so dense that a ‘collapse’ happens. This is when its gravity becomes so powerful that a huge amount of gas rushes towards it all at once.
Then, something unexpected happens…A massive explosion!

Protostar Formatio

In one giant blast, most of the collapsing gas gets thrown back outwards. In the center of the blast is a newly formed protostar! What’d happened was that some of the gas got so dense, it formed this new star. Then, like any star would, it pushed back on any leftover gas trying to crush it.

An image of an apple core, with the seeds exposed.

Let’s hope the only similarity between stars and apples is having a core. I really don’t want stars falling from trees.

That said, this new protostar isn’t really a true star yet. Fully grown stars carry out a process called fusion which is how they generate energy. Protostars do not, which makes them pretty weak. As a result, the stuff around them will keep trying to collapse. Each time the young star prevents a collapse, it grows a little bigger. That’s because some of the infalling gas remains with it.
Importantly, this growth also makes the protostar’s core hotter. In general, a star’s core heats up as it’s compressed. This matters a lot because a special transformation takes place when a protostar’s core reaches 10,000 degrees Kelvin.

Protostar to Main Sequence Star

That said, a protostar’s growth and related heating take a very long time. They start out at about 2000 degrees Kelvin, and the climb to 10,000 Kelvin can take them over 1 million years! But, once they get there, their core transforms. The protostar is then able to carry out nuclear fusion.

Even so, we still can’t call them real stars. They’re very unstable and continue to undergo rapid change as they get ready for the main sequence. So instead, we call them pre-main-sequence stars. It’s only once a pre-main-sequence star settles down that we finally have a fully grown star.

A digital image of a star.

Recipe for a star: Add matter and time, collapse gradually. Ready in about a million years.

The Possibility of Planets Forming

At this point, we’ve got a star. And stars are nice, but what about their planets? Interestingly, they form in much the same way as stars do and often right afterward. Most solar systems begin to take shape in the aftermath of star birth.

It’s important to note that much of the cloud which built up a star will remain around it after formation. What’s more, stars tend to attract large bodies of metal or rock. All of this matter can start to clump together in the same way that a protostar does. Rock and metals will build-up strong, dense planets (like Earth) while remaining gases will contribute to gas giants (like Jupiter).

An image of the planet Jupiter.

Some people call Jupiter a failed star. It’s a giant ball of gas, but not one dense enough to evolve into anything.

Other Great Resources:

The ESA on Star Birth: https://www.esa.int/esaKIDSen/SEMY06WJD1E_OurUniverse_0.html

More Facts on Star Formation: https://www.ouruniverseforkids.com/how-stars-are-born/

Cosmos4Kids on the Development of Stars: http://www.cosmos4kids.com/files/stars_develop.html

(Video) A Star is Born: https://www.youtube.com/watch?v=mkktE_fs4NA


Written by: Noah Louis-Ferdinand