Short Wave - A Star Is Born ... And Then What? Journey Through The Life Cycle of a star

Episode Date: December 6, 2023

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. Astrophysicist Sarafina El-Badry Nance has always been drawn to a particular star in Orion: Betelgeuse, a red supergiant nearing the end of it's life on the hunter's left shoulder. But what stages of life did Betelgeuse — or any star — go through before it reached this moment? Regina G. Barber talks to Sarafina about three winter constellations, and journey through the life cycle of a star. Curious about the night sky? Email us at [e-mail] — we'd love to hear from you!See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

Okay, when was the first time you remember finding Orion in the sky? Oh, that's a great question. Thank you. I wrote it. You're listening to Shortwave from NPR. As a kid, one of the first constellations I learned about is Orion. One of the most recognizable constellations in the sky. And soon after the sunsets, if you live in the northern hemisphere, you can find Orion near the eastern horizon on winter nights.

In Greek mythology, Orion is a lot of the ocean. is a legendary hunter. One myth says he was banished to the sky for boasting about how many animals he could kill, and that he and his hunting dogs eternally chased Taurus the Bull and the Pleity Sisters. Another says that the goddess Artemis was tricked into killing Orion with her arrow,

setting his image in the stars. When we peer into the sky now, we can see the over a dozen stars that form his constellation. The easiest to see are the three that line up to make his belt. You know, I had seen it before, but I didn't know what I was looking at. And I started studying the star Beetlejuice as a freshman.

And so my gaze was drawn upwards to that red star in Orion. That's Serafina El Badri Nance, an astrophysicist and an expert in Beetlejuice, another star in Orion. It's the upper left shoulder of Orion. It is a red super giant, so it literally looks red. to the naked eye, which makes it really easily found when you're looking for the star. And it's particularly interesting because it is very close and it is nearing the end of its life

when it will explode as a supernova. If you're looking up at Beetlejuice, coming to the end of its life, you might wonder, how did it get there? What stages of life does a star go through before it dies? The life cycle of a star is primarily determined by the mass of the star. So low-mass stars have very different fates than high-mass stars do. A low-mass star, stars smaller than our sun, will live longer than high-mass stars, like Beetlejuice. It's kind of like dogs.

Smaller dogs tend to live longer than big ones. And these really massive stars explode at the end of their lives. But don't worry. Our sun is not massive enough to explode at the end of its life. Instead, it will sort of get really big as a red giant, and then we'll fizzle out into what we call a white dwarf. So today on the show, it's a star party. Serafina and I walk you through three winter constellations and journey through the life of a star. I'm Regina Barber, and you're listening to Shortwave, the science podcast from NPR.

Okay, Serafina, let's start with the beginning of a star's life. How are stars born? So basically, stars are born in these stellar nurseries that we call giant molecular clouds. And they're sort of like the cradles of newborn stars. And basically, there are regions of gas and dust that clump together because of gravity. 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 proto star, which is sort of the nascent star. And then over the course of, you know, millions of years, the proto stars will sort of settle down and ignore,

fusion in their cores, which sort of sets the star on its life cycle as a real main sequence star or hydrogen burning star. Right. So in order for something to even be a star at all, like nuclear fusion has to happen, right, turning hydrogen into helium in its core. Right, exactly. Once it ignites hydrogen, the star becomes quote unquote alive. nuclear fusion is the lifeblood of a star. And basically what happens in the cores of stars is that elements and molecules collide with each other and create heavier and heavier elements as they do so. And their energy is released in the form of light that sort of shines through the star and that we see as starlight or in the case of our sun, sunlight. So that new, Nuclear fusion basically sets the tone of the star, and that nuclear fusion ignites once the star transitions from a protostar to a main sequence star.

Once stars start to fuse those elements in their core, they wink into existence. And this doesn't usually happen in isolation. Groups of stars are born from the same molecular cloud. And if you zoom back out to the larger scene of these constellations and look to the right of Orion, you will see Taurus. the bull. And within that constellation, you can catch a glimpse of the Pleiades sisters running from Orion and his dogs. It's an area with baby stars. So the stellar nursery in the Pleiades has basically hundreds of new stars, and they're blue because of the size and the temperature that they're born at. These baby stars and Pleiades, they're blue because they're born very hot. This makes sense if you think, about fire. Like a campfire is really red, maybe yellow, but it's not as hot as the blue flame

that comes out of a blowtorch. So blue stars are hotter than red stars, and new forming stars are sort of at the hottest parts of their existence, so they look very blue. And as the Pleiades or any stars form and move around, some stars will split off from their siblings. But those that stick together, they can form binary or even triinary systems. It's really dependent on what region of the giant molecular cloud that it's formed from, like, how close that nearest dense region is. So if two dense regions sort of form close together, then you, you know, more easily form a binary star.

Like Sirius, the star in the chest of Orion's largest hunting dog, Canis Major. With a quick look, you can probably see Sirius A, the brightest star. in the sky, but it's part of a binary system with a second much smaller star, Sirius B. Okay, so, Serafina, why is Sirius A so bright? Sirius is at the very beginning. It's a very young star compared to, you know, sort of the evolution of stars. So it's one of the closest stars to Earth. I think it's something like eight or nine light years away. Yeah, okay, let's compare Sirius to some older stars in Orion. Right? So what process is happening in the core of these middle-aged stars?

So nuclear fusion sets the sort of life stage of the star. Middle-aged stars, like the sun, have hydrogen fusing into helium in their cores. And they'll do that until the hydrogen in the center of the star runs out. Our sun is middle-aged star. It's fusing hydrogen to helium. And as a byproduct of that fusion, it emits. sunlight or starlight that we sort of experience every day. And yeah, middle-aged stars are relatively stable. Okay, so like middle-aged stars are fusing that hydrogen into helium in a very non-chaotic way, right? Yeah, exactly. And they stay there for a while. How long are stars

technically middle-aged of their lifetime? The majority of a star's lifetime is during its middle-age. So something like 90% of a star's life is spent in middle-aged. And then the last 10% is sort of this violent upheaval at the end. So our son is fusing hydrogen to helium for something like 10 billion years. So it's a very long, stable part of a star's life. Yeah. Just like me. Just 90% of my life is in middle age.

Yep. But one day I will be in that final 10%, right? Like Beetlejuice, sadly. And that sits in Orion's shoulder, right? Yeah, exactly. I would call Beetlejuice a star that is nearing explosion and is sort of an elderly star that will explode any time now, astronomically speaking. Okay. And we know that because of what's happening in its core, right?

Like, what is changing? So a dying star has reached the point beyond which it can no longer fuse heavy elements in its core. It cannot get hot enough to fuse any heavier elements. But there are still shells of the lighter elements that are undergoing fusion surrounding the core of the star. And there's more to learn about the end of a star from Beetlejuice. Because it's so big, it's going to have this dramatic death. So it's a very bloated star. And basically it has swollen as it gets older.

Beetlejuice will not just fall back in on itself, but then it'll explode as a supernova. And when is the estimate that Beetlejuice is going to explode? There have been lots of discussions around when that might happen. Some people anticipate it could be tomorrow night. And some people, you know, think more conservatively, I think studies are sort of pointing at 100,000 years or so, which might seem like a very long time. But astronomically speaking, that's, you know, quite quick. And, you know, I think we're all just sort of crossing our fingers and hoping that it goes off within our lifetimes. But who knows?

We actually have an example of something like this in 1054 AD. A star exploded. And what was left over was so bright you could see it in the daytime for about a month. And as it dimmed, you can see the debris from the explosion at night for almost two years. So can you tell us about Beetlejuice and what that might look like if it explodes? Yeah, when Beetlejuice explodes, it'll be visible during the day and the night for about a month and will continuously be visible throughout the next, I think, year. So it'll be something that won't harm us here on Earth.

The explosion is far enough away that we won't actually feel any sort of physical ramifications, but it'll be a beautiful light show that we'll be able to see for quite some time. What kind of life lessons can we learn from stars? 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. But change and even violent change, I think, in a star, you know, as it nears the ends of its life, it sort of experiences these crazy rapid mass loss, violent winds.

It can burp things. It can eject things. And it might seem as though that is, you know, very chaotic and that can have a negative connotation. But I think actually it's very normal, right? We all sort of undergo these periods of turbulence and chaos. And out of that can come something really beautiful. So I find a lot of comfort in knowing that. even these enormous stars experience something that we all experience at some points in our lives. Serafina, thank you so much for being a guide to the stars with me. Thank you so much for undergoing this journey with me. Before we head out, I want to take a minute to say thank you so much to our shortwave plus supporters and anyone listening who donates to public media. After all, public media means that you, the public, supports it. Everything you hear from the NPR network really does depend.

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explore NPR plus at plus.npr.org. This episode was produced by Rachel Carlson, edited by a showrunner, Rebecca Ramirez, and fact-checked by Brett Hansen. I'm Regina Barber. You're listening to Sherwave from NPR.