Star formation

Star formation is the amazing process where new stars are born. It happens in special places in space called molecular clouds, which are found in interstellar space. These clouds, sometimes called "stellar nurseries," 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 study the interstellar medium—the thin gas and dust that fills the space between stars—and giant clouds of molecules called giant molecular clouds. These clouds are the starting points for new stars. As the clouds collapse, they create early stars known as 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 orbiting around them, a field also known as planet formation. Most stars don't form alone; they usually come in groups called star clusters or stellar associations. Understanding how stars form helps us learn about the whole universe and how everything in it came to be.

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, and not much else.

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 under their own pull to create new stars.

Stellar nurseries

Spiral galaxies like the Milky Way contain stars, old stellar remnants, 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 massive 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 begin as small clouds of gas and dust in space. These clouds slowly pull themselves together because of gravity. As they collapse, they heat up and spin. The center becomes so dense that it forms a hot ball called a protostar.

The protostar keeps growing as more material falls onto it. Eventually, it gets hot enough for nuclear fusion to start, turning hydrogen into helium. This gives the star its own energy, and it becomes a true star. Smaller stars take longer to form, while bigger stars form more quickly.

Observations

Star formation is best studied using light beyond what our eyes can see. The early stages of a star’s life are hidden within clouds of gas and dust, often seen as dark spots called Bok globules against bright surrounding gas. Infrared light can pass through this dust more easily, allowing us to observe these hidden stars. Space telescopes like the Wide-field Infrared Survey Explorer have helped discover many young stars and star clusters, such as FSR 1184 and Majaess 98.

Scientists also use X-ray light to study young stars, as they shine much brighter in X-rays than older stars. This helps researchers count stars in regions where new stars are forming. We can directly observe star formation in our own Milky Way Galaxy, while in faraway galaxies we detect it using its unique spectral signature. Recent discoveries include a very distant galaxy forming stars at an incredible rate and signs of the earliest stars formed 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 collapse under gravity. As the cloud collapses, it spins and forms a flat disk around the new star, which helps gather more material.

Larger stars are trickier because their strong light can push away the material needed to form them. Scientists think that jets shooting out from these young stars help clear a path for the light to escape, allowing the star to keep growing. Observations show that many big stars also have these disks and go through bursts of growth. Some theories suggest that big stars might form when smaller stars merge 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. These filaments help gather gas and dust together, which can eventually lead to the birth of new stars.

Filaments play an important role in star formation by acting like pathways that collect material. Most early star-forming cores are found close to these filaments, supporting the idea that filaments help create the conditions needed for new stars to form.