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How Are Stars Formed?

Using Slooh’s Online Telescope and integrated NGSS aligned Quest learning activities, you can capture your own images of stars at different points in the stellar life cycle and make an infographic like the one above. Stars Like Ours is one of 60+ curriculum-aligned STEM Quest learning activities on Slooh for students 4th grade to college.

Slooh’s Online Telescope:

If you are an educator looking for fun, interactive ways to teach NGSS: HS-ESS1-1, HS-PS1-8, and HS-ESS1-3, as well as other standard curriculum codes related to astronomy, keep reading to the end for more information on the Stars Like Ours Quest and ways to easily integrate Slooh into your classroom.


How Are Stars Formed?

The formation of stars begins with the gravitational collapse of a giant molecular cloud, which are typically 15 to 600 light-years across, containing 10 thousand to 10 million solar masses of matter (one solar mass is equal to the mass of the Sun). Giant molecular clouds are very cold, with temperatures of only 10 or 20 Kelvin. These temperatures allow gas to become molecular. The clouds are mainly made up of molecular hydrogen, but they also contain dust and other atoms and molecules. When these clouds become massive enough, they begin to collapse in on themselves because of the force of their own gravity, a force that pulls all matter together.

The collapse occurs at different rates within the cloud, with rarefied regions collapsing slowly and dense regions collapsing faster. In the dense areas, hot balls of gas begin to form. These are called protostars, and their formation takes around 10 million years to complete.

Within a single protostar, the collapse of the cloud increases the internal pressure and temperature. Normally, this increase in pressure and temperature would result in the cloud expanding, but the extreme temperatures instead cause the hydrogen molecules to break apart into individual atoms, a cooling mechanism that allows the cloud to condense even further. A cooling mechanism is a way for an object or system to eliminate excess heat.

When a protostar accumulates enough mass and is compressed by gravity so that its temperature reaches at least 10 million Kelvin, the hydrogen in its core begins to fuse naturally, converting hydrogen into helium. When thermonuclear fusion begins, the protostar becomes a star.

But what exactly is fusion? Nuclear fusion is a process where two light atomic nuclei combine or fuse and create a heavier nucleus with some excess energy. A protostar primarily contains hydrogen atoms, which lack electrons at the high temperatures within the protostar, making them simply hydrogen nuclei, or protons. Usually, when two protons come near one another, their positive electric charges cause them to repel each other. However, when the temperature in the protostar reaches 10 million Kelvin, they are moving so quickly that they can actually run into each other, allowing fusion to begin.

Hydrogen fusion creates a massive amount of energy that pushes outward. This outward push balances the inward pull of gravity, and the newly formed star reaches a state of hydrostatic equilibrium in which it is no longer collapsing or expanding. This stable part of the star’s life is the Main Sequence phase, the phase in which the star will spend most of its life.

Star-forming region of Eagle Nebula

Large and Small

When massive protostars form, their stronger gravity causes them to contract rapidly and reach high temperatures in their core relatively quickly. The cores of these stars reach approximately 50 million Kelvin, which causes their rate of nuclear fusion to rise rapidly. These reactions generate the very large luminosities (the amount of energy emitted from the star’s surface) we see in massive stars. Because these high-mass stars perform nuclear fusion at higher rates, they also run out of hydrogen more quickly, making their lifespans shorter.

On the other hand, if a protostar is too small to reach a temperature of 10 million Kelvin, it becomes a brown dwarf. Brown dwarfs produce enough heat to appear to be cool, dim stars for a few million years, but they eventually fade away without being able to perform thermonuclear fusion. While brown dwarfs are not true stars, they are not planets either. Like stars, they produce their own heat, which planets do not do (we can only see planets because they reflect the light of nearby stars). So, because these bodies don’t fit into either category, they qualify for their very own classification!

How Often Are New Stars Formed?

Although it can be hard to observe new star formation in the Milky Way because of gas and dust obscuring our view, there are probably only around three or four new stars formed every year. However, some galaxies are like star factories, churning out hundreds of new stars every year! These are known as starburst galaxies.

Planet Formation

The formation of planets is directly related to the formation of stars. As a star is beginning its life, there is a leftover debris disk surrounding it made up of all the gas and dust that did not become a part of it. The microscopic grains of dust in this disk sometimes collide with each other and, on occasion, stick together. Over the next tens of millions of years, these clumps continue to gently collide with other material until they eventually become planets!


More About Slooh's Stars Like Ours Quest

In this quest, you will use Slooh's telescopes to capture images of low-mass stars at different points in their life cycle in order to explore the life and death of stars like the Sun. This quest will culminate with the construction of a model of the lifespan of a star like our Sun using your images and text explanations.

Learning Objectives

By the end of this Quest, students will be able to answer the following questions:

  • How do stars of similar mass to the Sun form?

  • What is fusion, and what happens when this takes place in main sequence stars and giant stars?

  • How do stars of similar mass to the Sun end their lives? What happens to the remnant star?

Vocabulary Words

Standards Addressed

NGSS Performance Expectations

HS-PS1-8, HS-ESS1-1, HS-ESS1-3


RST.9-10.1, RST.9-10.2, RST.9-10.3, RST.9-10.4, RST.9-10.7, RST.9-10.9, RST.9-10.10, WHST.9-10.2.B, WHST.9-10.2.C, WHST.9-10.2.D, WHST.9-10.2.E, WHST.9-10.2.F

Related Slooh Quests

  1. Our Radiant Star

  2. Out With a Bang

  3. There Goes the Sun

More About Slooh’s Astronomy NGSS Aligned Learning Activities

Slooh’s Online Telescope is a learning platform designed to support any educator in teaching astronomy to meet NGSS requirements by collecting and analyzing real-world phenomena. No previous experience with telescopes is necessary to quickly learn how to use Slooh to explore space with your students.

You can join today to access Slooh's Online Telescope and all 60+ Quest learning activities if you are able to make astronomy a core subject of study for the semester or year. If you only have a few weeks to study astronomy, we also have a curriculum designed to fit your busy academic schedule and budgetary limitations. To learn more about our offers, click here.

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