How are Stars Formed — Reading Comprehension

Star formation in the universe begins inside vast clouds of gas and dust known as nebulae. These enormous regions, sometimes called stellar nurseries, contain the raw materials for creating new stars. The Orion Nebula is one of the brightest and most studied examples, observable even with the naked eye from Earth. Understanding how stars are born in these nurseries helps scientists explain the life cycle of stars, the origins of planets, and the evolution of galaxies.

Gravity and the Birth of Stars
Within a nebula, certain areas become denser than others due to small disturbances or the death of previous stars. The force of gravity pulls the gas and dust in these dense regions closer together. As the material collapses, it spins faster because of the conservation of angular momentum, a physical principle that keeps spinning objects rotating as they shrink. The spinning causes the cloud to flatten into a disk with a bulging center. The central region, known as a protostar, heats up as the material compresses. Temperatures rise dramatically, sometimes reaching millions of degrees Kelvin. During this phase, the protostar glows from internal heat but does not yet create energy by nuclear fusion.

From Protostar to Main Sequence Star
The next key stage is the T Tauri phase, when the young star is still gathering mass and is very active. When the core temperature of the protostar approaches about 10 million Kelvin, a process called nuclear fusion begins. Here, hydrogen atoms in the core fuse to form helium, releasing vast amounts of energy as light and heat. This nuclear reaction creates an outward pressure that balances the inward pull of gravity. At this moment, the star becomes a main sequence star—like our Sun—and is considered truly "born." The leftover material in the disk can clump together, forming planets, asteroids, and comets in a structure called a protoplanetary disk.

Variety in Star Formation and Its Importance
The timeline for star formation depends on the mass of the collapsing region. For stars similar to our Sun, it takes about 50 million years to reach the main sequence. More massive stars form much faster, while smaller stars can take hundreds of millions of years. Astronomers use telescopes to observe nebulae and protostars at various stages, confirming theories about star birth through direct evidence and computer models. Understanding star formation also reveals how elements are distributed across the universe and how planetary systems, including our own solar system, come into existence.

Studying stellar nurseries shows how interconnected the universe is—each star formed enriches space with new elements, paving the way for future generations of stars and planets. The birth of stars is a key process in galactic evolution and helps explain the diversity of worlds we observe.

Interesting Fact: The Orion Nebula is about 1,344 light-years from Earth and contains thousands of young stars forming right now!

What is a nebula?

What causes the material in a nebula to start collapsing?

Which stage comes right before a star becomes a main sequence star?

What is the main process that powers a main sequence star?

What does the term 'stellar nurseries' mean in the passage?

What happens to leftover material in the protoplanetary disk?

Which of the following best explains why the collapsing gas spins faster?

True or False: All stars take the same amount of time to form.

True or False: The Orion Nebula can be seen without a telescope from Earth.

Why is studying stellar nurseries important to science?