The First Generation Stars

12 Billion Years Ago.

HeliumS_1THIS PLAQUE REPRESENTS ATOMS OF HELIUM in the gas cloud of the early universe. After a time, gravity made the cloud lumpy. The biggest lumps became stars. Stars are formed when gravity becomes so strong that small atoms are squeezed together to form bigger ones, giving off huge amounts of energy.

The first generation stars eventually burned themselves out and imploded, scattering atoms into space. Our sun and the planets of our solar system were formed from these scattered remains. The creation of the solar system, 9.4 billion years after the first stars, is the subject of the next station.

 

IN ITS EARLY STAGES, the universe is thought to have existed as an expanding cloud of only the two lightest elements, hydrogen and helium. Very minor differences in the density of the cloud caused the gas to condense through gravity. This formed dense masses, squeezed so tightly by gravity that atoms of hydrogen, which have a single proton in the nucleus, fused to form helium, which has two.  This nuclear fusion is what powers the stars, radiating energy across the universe.

The first stars ignited about 12 billion years ago. As they developed, they began to fuse larger atoms at the core. First helium fused to beryllium, then to carbon and oxygen, each level of fusion giving out further energy.

Eventually the stars developed a series of layers like an onion, with heavier and heavier elements being fused in each successive layer until a mass of iron formed at the core.

After billions of years, the iron in the core of the first generation stars built up to point where it stifled further nuclear fusion. Unsupported by the energy of nuclear fusion, the cores collapsed under the immense pressure of their own gravity.

The shock wave of this implosion causes the rest of the star to explode as a supernova, spewing atoms forged in the nuclear furnace out into space.

Our own solar system, the sun and all the planets, was formed from this debris, 9.4 billion years after the formation of the first generation stars. That will be the subject of the next station.