The Lives, Times, And Deaths Of Stars

Who among us doesn’t covertly read tabloid headlines when we pass by them? OK, you don’t. But the rest of us, yeah we probably do. But if you’re really looking for a dramatic story, instead of looking to Hollywood, turn you face to the sky and check out the real stars (do not look directly into the sun). From birth to death, the burning spheres of gas that light the night sky and the one that powers our daytime lives experience the most extreme conditions our cosmos has to offer.

All stars are born in clouds of dust and gas like the Pillars of Creation in the Eagle nebula (pictured below). In these stellar nurseries, clumps of gas form, pulling in more and more mass as time passes. As they grow, these clumps start to spin and heat up. Once they get heavy and hot enough (somewhere in the realm of 27 million degrees Fahrenheit or 15 million degrees Celsius), nuclear fusion starts in their cores. This process occurs when protons, the nuclei of hydrogen atoms, squish together to form helium nuclei. This releases a LOT of energy, which heats the star and pushes against the force of gravity. And with this violent reaction, a star is born.

Credit: NASA, ESA and the Hubble Heritage Team (STScl/AURA)

From that point on, a stars lifecycle depends on how much mass they have. Scientists typically divide stars into three categories: low-mass, high-mass and the lesser used intermediate-mass. We’ll discuss the first two for simplicity’s sake.

Low-mass Stars: These stars have a mass about eight times that of our Sun’s or less and can burn steadily for billions of years. As it reaches the end of its life, its core runs out of hydrogen to convert into helium. Because the energy produced by fusion is the only force fighting gravity’s tendency to pull matter together, the core begins to collapse. But squeezing the core also increases its temperature and pressure, so much so that its helium starts to fuse into carbon, which also releases energy. The core rebounds a little, but the star’s atmosphere expands a lot. This eventually causes the star to turn into a red giant star and destroy any nearby planets. Our sun will also go through this process but it’s a few billion years away so we don’t have to worry about it just yet.

Red giants are unstable and begin pulsating, periodically inflating and ejecting some of their atmospheres. Eventually, all of the star’s out layers blow away, creating an expanding cloud of dust and gas misleadingly called a planetary nebula (there are no planets involved save for the ones that were orbiting the star and were already destroyed).

Credit: NASA, ESA and the Hubble Heritage Team (STScl/AURA)

All that’s left of the star is its core, now called a white dwarf. This star is a roughly Earth-sized stellar cinder that gradually cools over billions of years. If you could scoop up a teaspoon of its material, it would weigh more than a pickup truck. (Scientists recently found a potential planet closely orbiting a white dwarf. It somehow managed to survive the star’s chaotic, destructive history!)

High-mass Stars: These stars have a mass eight times the sun’s or more and may only live for millions of years. (Rigel, a blue super-giant in the constellation Orion, pictured below, is eighteen times the Sun’s mass.)

Credit: Rogelio Bernal Andreo

A high-mass star starts out doing the same things as a low-mass star, but it doesn’t stop at fusing helium into carbon. When the core runs out of helium in a high-mass star, it shrinks, heats up and starts converting its carbon into neon, which releases energy. Later, the core fuses the neon it produced into oxygen. Then, as the neon runs out, it fuses the oxygen into silicon. Finally, the silicon is fused into iron. All of these processes produce energy that keeps the core from collapsing, but each new fuel buys it less and less time. By the point silicon fuses into iron, the star runs out of fuel in a matter of days. The next step would be fusing iron into some heavier element, but doing so requires energy instead of releasing it.

The stars iron core collapses until forces between the nuclei push the brakes, and then it rebounds back to its original size. This change creates a shock way that travels through the star’s outer layers. The result is a huge explosion called a supernova.

What’s left behind depends on the star’s initial mass. Remember, a high-mass star is any star with a mass more than eight times that of our sun. That’s a HUGE range! A star on the lower end of this spectrum leaves behind a city-sized, super-dense neutron star. (Some of these weird objects can spin faster than blender blades and have powerful magnetic fields. A teaspoon of their material would weigh as much as a mountain!!)

At even higher masses, the star’s core turns into a black hole, one of the most bizarre cosmic objects out there. Black holes have such strong gravity that light can’t escape them. If you tried to get a teaspoon of material to weigh, you wouldn’t get it back once you crossed the event horizon — unless it could travel faster than the speed of light and we don’t know of anything that can!

The explosion also leaves behind a cloud of debris called a supernova remnant. These and planetary nebulae from low-mass stars are the sources of many of the elements we find on Earth. Their dust and gas will eventually one day become a part of other stars starting the whole process over again. So the next time you feel incredibly lost or alone, remember that we’re all connected by the star stuff we’re made from!

That’s a very brief summary of the lives, times and deaths of stars.

Article Credit: NASA Universe