Paul Levesque Popular Astronomy Club
Our sun, which rises and sets each day and determines the course of the Earth's seasons, is just one of more than 100 billion stars found in the Milky Way galaxy in which our Solar System resides.
The Milky Way, in turn, is just one of the more than 200 billion galaxies believed to exist in the known universe, and these galaxies also contain billions of stars.
Given these incomprehensible numbers, it's no surprise that there are many different types of stars, ranging widely in size and temperature, and in appearance as seen from Earth. Still, every one of the stars out there -- the ones we see, the ones we don't see and the one our planet rotates around -- all share basically the same origin story.
Just like us, stars are born and have a limited lifespan. And just as you'll find newborn babies in a hospital nursery, you'll find newborn stars in areas of the Milky Way and other galaxies that astronomers refer to as "stellar nurseries."
Stellar nurseries are clouds of gas and dust, mostly made up of hydrogen, that cover vast regions of a galaxy. Most stretch at least 150 light-years from end to end; keep in mind that a light-year is a measure of distance based on how far a beam of light travels in one Earth year (one light-year is equal to approximately 6 trillion miles).
The law of gravity applies in stellar nurseries, just as it does on Earth. So, over time, gravitational attraction causes some of the gas and dust particles within a stellar nursery to come together and coalesce.
Eventually, a core can be formed out of the coalescing particles, made up mostly of hydrogen atoms. As these atoms converge and collapse inward, pressure and temperature increase.
Temperature is based on the kinetic energy of atoms; the faster the atoms are vibrating, the higher the temperature. So as the atoms of a gestating star press inward, the temperature rises along with the pressure.
The nucleus of a hydrogen atom consists of just one proton with a positive charge. Since the core of a star being formed is made up largely of hydrogen atoms, these atoms should repel one another, as like-charged particles normally do.
However, the temperature within a birthing star can rise to millions of degrees Fahrenheit as its core continues to collapse. At these extreme temperatures, the protons within hydrogen atoms vibrate at a very fast rate. This provides enough energy to overcome the natural repulsion of like charges and causes the protons to stick together as they bump into one another.
This process is known as fusion, a word describing the fusing together that happens as a star is formed. Through fusion, hydrogen atoms merge and create helium atoms, which have two protons at their core.
As the fusion process continues, a tremendous amount of energy is released in the form of radiation. This radiation creates a pressure of its own as it tries to escape the core of the protostar. The radiation pressure is balanced by the gravity collapsing the particles of the protostar into its core.
When the core of the protostar ignites, "a star is born," shining bright and radiating heat because of the release of fusion energy. Stars are really just enormous thermonuclear reactors that convert hydrogen in their cores to helium.
The balancing act between gravity trying to contract the star and radiation pressure streaming out from the star's core, continues throughout the lifetime of a star. What was once just an amorphous cloud of gas has contracted into an object we can identify as a star, which can shine for millions or billions of years as its hydrogen is fused into helium.
As the star ages, the hydrogen fuel is consumed, and helium "ash" builds up in the core. This reduces the amount of hydrogen fusion and decreases radiation pressure.
As less energy is released, gravity takes over and collapses the star inward, creating higher temperatures and pressures at the core. The higher temperature now allows fusion of the helium ash and remaining hydrogen into more complex elements like oxygen and carbon, on up to iron, which contains 26 protons.
Fusing heavier elements such as iron consumes energy and causes a further decrease in the number of hydrogen and helium atoms. Stars undergoing this process can eventually explode, releasing back into space what's left of the elements produced over the star's lifetime.
The remnants of a star can find their way into stellar nurseries where new stars can be formed, and these new stars can contain heavier elements that find their way onto planets such as Earth.
This means, as Carl Sagan once famously said, that we are all made of "star stuff" -- of elements formed within the cores of distant stars that are now gone. Because these stars were born many billions of years ago, we too were born, much more recently of course.
Stellar nurseries, the birthplaces of stars yet to be formed, can be seen from Earth in the form of nebulas, seen through a telescope as fuzzy patches of the night sky that look similar to clouds. No surprise, then, that "nebula" comes from the Latin word for cloud.
Earthly clouds can obstruct our view of nebulas; when we do observe a nebula, though, let us be mindful that all we are and all we can see came from a place like this.
You can view nebulas and other celestial objects at the monthly public observing session held by the Popular Astronomy Club at Niabi Zoo. The next one, which is also the next-to-last for the year, is scheduled for Saturday, Oct. 19, beginning at sunset.
You can find out more about PAC by checking us out on Facebook or visiting our website at https://www.popularastronomyclub.org/.
These photos of stellar nurseries were taken by members of the Popular Astronomy Club. Note that long time exposures were used to take these photos through a telescope with the naked eye, these nebulas would look like fuzzy patches.