A star is born ... and then what? A journey through the life cycle of a star

Soon after the sun sets on winter nights, if you live in the northern hemisphere you can look into the sky and find the Orion constellation near the eastern horizon.

In Greek mythology, Orion is a legendary hunter. One myth says he was banished to the sky for boasting about how many animals he could kill. He and his two hunting dogs eternally chase Taurus the bull and the Pleiades sisters as punishment — never able to catch them. Another myth says the goddess Artemis was tricked into killing Orion with her arrow and set his image in the stars.

If you look up at the sky tonight, you might recognize Orion by the three stars that line up to make the hunter's belt.

Astrophysicist Sarafina El-Badry Nance was drawn to one star in Orion in particular: Betelgeuse, a red supergiant on the hunter's left shoulder. El-Badry Nance says this star is nearing the end of its life, when it will explode as a supernova.

But what stages of life did Betelgeuse — or any star — go through before it reached this moment?

A star is born

Stars are born within clouds of dust scattered throughout galaxies.

"They're regions of gas and dust that clump together because of gravity," El-Badry-Nance says. "And as the density of these regions pulls more and more gas and dust towards it, that pressure can cause them to collapse under their own weight and create what we call a protostar, which is sort of the nascent star."

Over time, these protostars begin fusing hydrogen into helium in their cores. The energy from this process keeps stars from collapsing under their own weight.

"Their energy is released in the form of light that sort of shines through the star and that we see as star light or, in the case of our sun, sunlight," El-Badry Nance says.

Stars spend the majority of their lifetimes in middle age, as it's the most stable part of their life cycle. Take the sun. It's a middle-aged star and scientists estimate it will continue to burn hydrogen for about another five billion years.

A star dies

When a star runs out of hydrogen fuel for nuclear fusion, its core begins to collapse.

It enters the final stage of its life.

At that point, the outer layers of the star expand and cool, turning it into a swollen, bloated star. Betelgeuse is an example of a star at the end of its life, and El-Badry Nance says that since it's so big, it's going to have a dramatic death.

"Betelgeuse will not just fall back in on itself, but then it'll explode as a supernova," she says.

Scientists don't know exactly when the star will explode, but when it does, it will be visible to us on Earth for a long time.

Across the life and inevitable death of these beloved stars, El-Badry Nance says there are important life lessons to learn.

"First and foremost: Everything changes. Right? There's nothing static in the universe, really — even though it might feel that way because those timescales are so much longer than our own," she says. "We all sort of undergo these periods of turbulence and chaos and out of that can come something really beautiful."

Curious about the night sky? Email us at shortwave@npr.org — we'd love to hear from you!

Listen to Short Wave on Spotify, Apple Podcasts and Google Podcasts.

Today's episode was produced by Rachel Carlson. It was edited by Rebecca Ramirez. Brit Hanson checked the facts. Ko Takasugi-Czernowin was the audio engineers.

ncG1vNJzZmivp6x7r7zRZ6arn19nfXN%2FjmppaGhmZH5yhZdyZ3FvaW18rbXFnmScsZOhsm67xWaYZquklr9uv9Oeo6WZomKyt7vLrquip55ivLO1zqdkm52kmrmosdSsnA%3D%3D