Star formation

Star formation is the amazing way new stars are born. It happens in special places in space called molecular clouds. These clouds are found in interstellar space. They have dense areas that collapse under their own gravity. As they collapse, they form hot, glowing balls of gas that become stars.

This process is a big part of astronomy, the science that studies space and everything in it. Scientists look at the interstellar medium—the thin gas and dust between stars—and giant clouds of molecules called giant molecular clouds. These clouds are where new stars start. As the clouds collapse, they make early stars called protostars and young stellar objects.

Star formation is also linked to how planets form, because the same clouds that make stars can also create planets around them. This is known as planet formation. Most stars do not form alone; they usually come in groups called star clusters or stellar associations. Learning about star formation helps us understand the whole universe and how everything in it began.

First stars

Star formation is grouped into three types called "Populations." Population III stars were the very first stars, forming from simple hydrogen after the Big Bang. Scientists think these stars were made only of hydrogen and helium.

Later, Population II stars formed from the remains of these first stars, and they created heavier chemical elements. Finally, Population I stars are younger stars, rich in metals (elements besides hydrogen and helium), like our Sun. These stars began forming when hydrogen in areas with more gravity, called dark matter halos, came together and collapsed to create new stars.

Stellar nurseries

Spiral galaxies like the Milky Way contain stars, old stars that have ended their lives, and a thin fog of gas and dust called the interstellar medium. In this fog, denser areas form clouds where stars are born. These clouds are mostly hydrogen and helium, with tiny amounts of heavier elements made inside older stars.

Inside these clouds, especially the colder ones, new stars begin to form. The Orion Nebula is a famous place where big stars are being created, while the ρ Ophiuchi cloud complex is a site for smaller stars. Very dense, dark clouds called Bok globules can also hide newborn stars. When these clouds become heavy enough, they collapse under their own gravity, forming many stars at once.

Protostar

Main article: Protostar

Stars start as tiny clouds of gas and dust in space. These clouds slowly come together because of gravity. As they get closer, they get warmer and start to spin. The middle becomes so squeezed that it makes a hot ball called a protostar.

The protostar keeps getting bigger as more stuff falls onto it. Finally, it gets hot enough for something called nuclear fusion to start, changing hydrogen into helium. This gives the star its own light and heat, and it becomes a real star. Little stars take longer to form, but bigger stars form faster.

Observations

We learn about how stars are born by looking at light that our eyes cannot see. The first steps of a star’s life happen inside clouds of gas and dust. These clouds often look like dark spots against brighter gas around them. Special light called infrared can pass through this dust, helping us see the hidden stars. Space telescopes like the Wide-field Infrared Survey Explorer have found many young stars and groups of stars, such as FSR 1184 and Majaess 98.

Scientists also study young stars using a type of light called X-ray. Young stars shine very brightly in X-rays, which helps us count them in areas where new stars are being born. We can watch stars form right here in our own Milky Way Galaxy. In galaxies far away, we find new stars by looking at their special light patterns. Recent discoveries have found a galaxy very far away that is making stars quickly and clues about the first stars in the universe.

Low mass and high mass star formation

Stars of different sizes form in slightly different ways. Small stars form when clouds of gas and dust in space come together because of gravity. As the cloud comes together, it spins and makes a flat disk around the new star. This disk helps the star collect more material.

Larger stars are harder to form because their bright light can push away the material they need. Scientists think that jets shooting out from these young stars help let the light escape, so the star can keep growing. We can see that many big stars have these disks and sometimes grow very fast. Some ideas say that big stars might form when smaller stars join together.

Filamentary nature of star formation

Simulations show that long, thin structures called filaments often form when a fast shockwave moves through a cloud of gas. This can happen when a supernova explodes or a H II region expands.

Filaments help gather gas and dust together, which can eventually lead to the birth of new stars.

Filaments act like pathways that collect material. Most early star-forming cores are found close to these filaments, showing that filaments help create the conditions needed for new stars to form.