Famed astrophysicist Carl Sagan once remarked, “We are made of star stuff,” meaning that everything material we know is composed of chemical elements whose origins lie in the cosmos.
Nucleosynthesis is the term for the processes underlying these origins. Some forms of nucleosynthesis occurred eons ago, but others continue today. How does nucleosynthesis work?
One form occurred shortly after the Big Bang that birthed the universe. At this time, the universe was a roiling plasma of quantum particles, seething at an infernal two trillion degrees (Kelvin). Over the next twenty minutes, the plasma cooled enough to congeal into the first elements, hydrogen and helium. These became the most abundant elements in the cosmos, comprising 98% of all observable matter today. They also became the building blocks of stars, as the universe cooled further over the next few billion years.
Other forms of nucleosynthesis lie within stars themselves. Stars are held together by gravity. At their cores, the pressure is sufficiently intense to fuse hydrogen and helium atoms into heavier elements. Some elements, like oxygen, gradually percolate to the star’s surface over time, to be radiated into space. Others remain trapped until the star’s demise. Low-mass stars expel their outer layers as they die, forming planetary nebulae containing carbon, nitrogen, and xenon. Heavier stars die more explosively, as dramatic novae or cataclysmic supernovae, producing heavier elements like iron, nickel, and zinc.
Some supernovae leave behind neutron stars, objects so incredibly compressed that their atoms are crushed into neutrons. Occasionally, neutron stars collide with such colossal force that the neutrons are recombined into very heavy elements, like iridium, lead, and plutonium. The force also briefly warps space itself, as gravitational waves. Astronomers spotted such an event, 130 million light-years away, in August 2017. The spectacle, dubbed GW170817, generated an estimated ten Earth masses' worth of gold and platinum!
Elements in interstellar space accrete into dust clouds that eventually condense to form stars and planets. On at least one planet we know and love, such star stuff gave rise to life.
So never let anyone tell you that you are not a star. Everyone is a star, or at least of the stars. We are all equal on the cosmic scale.
Western Slopes Skies is produced by members of the Black Canyon Astronomical Society. This episode was written by Michael T. Williams and voiced by Art Trevena.
Web links of interest:
Where Your Elements Came From