Big Bang Series Part 2 - How Stars Form

You may not realize it, but stars are the engines that drive the universe – they always have been. From 100-200 million years after the Big Bang occurred, during the Matter Era of our universe, tiny hydrogen and helium atoms combined to form massive stars. Here I will give you an overview of how stars were born from these minuscule atoms. It is a fascinating and wondrous process.  

 Step 1: Giant gas clouds 

In the early stages of our universe, hydrogen and helium atoms began to clump together into small molecules. As time passed, some of these molecules cooled, reaching temperatures lower than 100 degrees above absolute 0 (so less than -170 °C).  This allowed these molecules to clump together into small gas clouds. Because of gravity, gas clouds began to combine, forming larger gas clouds. Eventually, giant ones called interstellar clouds were formed and floated around the universe. These were light years across in length! 

Step 2: Cooling and heating 

In some pockets of these interstellar clouds, temperatures reached to around 10 degrees above absolute 0 (around -260 °C).  When these pockets cooled, gravity caused them to collapse on themselves.  During this collapsing, gas rapidly accelerated into a small area, causing immense amount of heat (when objects move, they generate energy in the form of heat).  These collapsing pockets reached temperatures of 15 million °C !  

Step 3: Fusion 

When the gas pockets reached 15 million °C , interesting things happened. First, hydrogen atoms, moving at such high speeds, fused to other hydrogen atoms creating helium. When this happened, massive amounts of energy was released in the form of more heat, which escaped outward in the form of light. This is the light we see from stars! So, if you were to go inside a star, towards its center would be fusing hydrogen atoms releasing tons of energy. The outer layers of a star are these energies being released as heat and light.  

Step 4: Death 

Stars last anywhere from a few million years to over ten billion years. It all depends on how big the star is. Remember, a star’s energy – its heat and light – comes from fusing hydrogen atoms. The more hydrogen atoms that initially come together, the more energy a star will generate, and the bigger it will be.  Bigger stars burn through their hydrogen fuel faster than smaller stars. When a typical star runs out of fuel, it dies, expanding and contracting over billions of years. During this expanding and contracting, helium is fused into new elements in the core of the star. Eventually, the dying star eventually releases all its gas and many of the elements it formed in a nebula. Over the billions of years of our universe, nebula have allowed other stars to be formed, creating even more elements..  

Step 5: Elements 

The elements that stars have created and eventually released into nebulae are the materials that make up all planets, moons, and asteroids. If you take a look at a periodic table, most of the elements you’ll see came from stars! 

Picture Source: cfa.harvard.edu