History #7: Star Formation

This post continues an ongoing series about big history. It follows the structure of the college-level course developed by historian David Christian.

In the last post, we explored how about 13.7 billion years ago, an unimaginable inflation of space, time, matter, and energy occurred know as the Big Bang. In those earliest microseconds of existence, the universe was so hot that matter and energy blended together in a kind of plasma soup. After a few hundred thousand years, the universe had cooled enough for protons and electrons to combine into simple atoms. The most abundant of these atoms being hydrogen and helium. Vast clouds of these atoms slowly populated the universe. If the story ended here, our universe would have remained dark, cold, and boring. The story didn’t end here.

Lighting up the darkness

The tiny variations in the density of matter throughout the universe allowed gravity to do its work. The vast clouds of hydrogen and helium began to clump together in ever denser regions. The denser they became, the more pressure and heat was produced. Temperatures eventually reached a point where the protons and electrons split apart into a plasma once again. At about 10 million degrees Celsius, hydrogen atoms began to fuse into helium atoms. This process of nuclear fusion released a huge amount of energy that prevented the cloud from collapsing further.

About 100 million years after the Big Bang, or 36 days on our 13 year time scale, the first stars began to light up. About 1 year after the Big Bang on our 13 year time scale, the universe began to look like what we would imagine, lightly sprinkled with galaxies containing hundreds of billions of stars.

The engines of complexity

Stars continued fusing hydrogen into helium until they ran out of hydrogen. At this point, there was nothing keeping the cloud from collapsing in on itself and gravity won out. The helium atoms collapsed into a region even denser than before and temperatures reached a level that allowed for the fusing of helium into carbon. Depending on the size of the initial cloud, this process repeated and created all the elements up until iron.

Elements heavier than iron cannot be created in stars. There just isn’t enough energy. But when giant stars exhaust their fuel and collapse, a huge explosion occurs known as a supernova. The energy released from a supernova is equivalent to that of a billion stars, and allowed for the creation of all the elements in the periodic table.

The ashes of these exploding stars fertilized the universe with elements that would go on to form complex molecules and compounds. Everything is made of star stuff.


Tiny differences in the density of matter in the early universe allowed for the formation of complex stars. Stars allowed for the formation of complex elements. Elements allowed for the formation of complex molecules and compounds. Molecules and compounds allowed for the formation of complex life. We will see how in future posts.



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