(This is an excerpt from "Evolution of a 1.25 Solar Mass Star" by Michelle Babcock, Copyright 2018)
“The Cosmos is rich beyond measure: the total number of stars in the universe is greater than all the grains of sand on all the beaches of the planet Earth.” —Astrophysicist Dr. Carl Sagan
Look up at the sky on a clear night, and you may see dozens or hundreds of stars with the naked eye, depending on the amount of ambient light in your area. If you’re lucky enough to visit a dark sky area with little or no light pollution at some point in your life, you may see thousands of stars, along with our Milky Way galaxy.
From planet Earth, our edge-on view of the Milky Way galaxy appears as if a giant paint brush of light were dragged from one horizon to the other. This streak of milky light in our dark sky is made up of hundreds of billions of stars — somewhere between 100 and 400 billion — an unimaginable number.
Each star, in a cosmic sense, is born, lives, and dies, over a timescale of billions of years. Around those stars, an estimated 160 billion planets orbit other suns. In such a vastness of space and immensity of time, it can be difficult to grasp how these massive objects with astronomical timelines relate to us humans, who live for a relatively short time on one small planet, orbiting an average star.
“We are star stuff harvesting sunlight.” —Sagan
On closer inspection, it’s easy to find how we are profoundly connected to the stars in more ways than one. We depend on the sun for light, for energy, for life. Without it, all plant and animal life on our planet would cease to exist. It gives us warmth, and is crucial to the environment in which our planet’s plants and animals thrive. Not only is our star one of the reasons life here on earth is so hospitable, we are also connected chemically to the story of stars.
“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of star stuff.” —Sagan
Our sun is a precious commodity to life on earth, and because of this and its close proximity to us, it’s the star we know most about. In fact, when astronomers study other stars in our galaxy and universe, they use our sun as a way to measure the mass of other stars: this is called “solar mass”. Our sun is one solar mass, or “1.00𝓜☉”.
In the following pages, we will explore the evolution of a 1.25𝓜☉ star, at some points comparing it to a 1.00𝓜☉ star similar to the sun. We will follow the journey of this 1.25𝓜☉ star from what astronomers liken to its conception and birth in stellar nurseries called nebulae into the protostar stages, all the way to its death.
Depending on the initial mass of a star, whether it’s large or small, it may die in one of a few ways. Low mass stars, between 0.5𝓜☉ and 8𝓜☉, end up ejecting a planetary nebula and leaving behind their naked, dense core, called a white dwarf. High mass stars, with greater than 8𝓜☉, will experience an astronomically violent explosion called a supernova, and will end up as either a neutron star or black hole.
Evolution of Stars, Courtesy of ROOTS Magazine (https://www.casopisroots.cz/pozorovani-nocni-oblohy-duben/)
Our 1.25𝓜☉ star will end its life as a white dwarf after ejecting a planetary nebula, much like the eventual death of our own 1.00𝓜☉ sun. In the following pages, we will follow the path of this star’s evolution, gaining an intimate understanding of its birth, life, and death. We’ll use our imagination to visualize each stage, alongside physics and mathematics to present an accurate analysis of such stages.
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