Short Wave - Some Stars Explode As They Die. We Look At Their Life Cycle

Episode Date: June 25, 2024

This summer, scientists have their eyes and telescopes trained on the small constellation system T Coronae Borealis. They think it will explode as part of a periodic nova — a once-in-a-lifetime event according to NASA scientists. And so, with the help of astrophysicist Sarafina El-Badry Nance, we continue our journey farther and deeper into spacetime with a look at the stars: How they're born and how they die. Sarafina has always been drawn to one particular star: Betelgeuse, a red supergiant in the shoulder of the constellation Orion that is nearing the end of its life. What stages of life did Betelgeuse — or any star — go through before it reached this moment? This episode is part of our series Space Camp — all abut the weird, wonderful phenomena in our universe. Check it out here: https://npr.org/spacecampCurious 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

You're listening to Shortwave from NPR. Hey, J.R. Waivers, it's Regina Barber, your resident astrophysicist, here with the next installment of Space Camp, all about the life and death of stars. And this summer in particular is a very exciting time to keep your eyes on the stars. That's because T. Corona Borealis, a star that's usually invisible to the naked eye, is set to experience a Nova event anytime between now and September. Up close, it's a thermal nuclear explosion, kind of like a hydrogen bomb. But here on Earth, it'll look like a bright new star appearing out of nowhere. T-Corona Borealis is a recurrent nova, which means it flare is up repeatedly, but doesn't completely destroy itself in the process.

The last time we saw it flare up was almost 80 years ago, in 1946. But humans have been watching other stars explode for much, much longer. So humans have seen stars exploding with the naked eye for centuries, and there are records of these explosions. Some of them are literally etched into cave drawings. Some of them are on, you know, old records. It's, I mean, it's remarkable to see how civilizations, even at that point, have a record of exploding stars. That's Serafina El-Baudrean. She's an astrophysicist and an expert.

in supernovas, the final destroying explosion of massive stars. And she studies one star in particular, Beetlejuice. 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 constellations as we 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 protostars will sort of settle down and ignite 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 nuclear fusion basically sets the tone of the star, and that nuclear fusion ignites once the star transitions from a proto star 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. 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 trinary systems, like T. Corona Borealis, which we mentioned earlier. 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? Serious 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-caotic 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, like, violent upheaval at the end. So our sun 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 be. It 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, 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. We'll be back tomorrow with our regular shortwave, and back Tuesday with our next installment of the Space Camp series. And it's going to feature the closest stars to Earth now that we've had this explainer on the life cycle of stars. Here's a sneak peek from one of our experts. Hey, Gina. It's Mike Wong, your science officer, back on Earth. I hope you're safely traveling all the way between our solar system and Alpha Centauri. Just to give you a heads up for what you'll find when you get there, Alpha Centauri, is a

a three-star system with Alpha Sanari A, B, and C. C is sometimes called Proxima Centauri, because it's technically the closest star to Earth, and it's a dim, red dwarf with an Earth-sized planet going around it in its Goldilocks zone. Please send pictures home. Thanks. Bye. The Space Camp version of this episode was produced and fact-checked by Hannah Chin. It was engineered by Valentina Rodriguez-Sah. The original episode was produced by Rachel Carlson, edited by our showrunner Rebecca Ramirez, and fact-checked by Britt Hansen. Special thanks to our friends at the U.S. Space and Rocket Center.

I'm Regina Barber, and you're listening to Shortwave from NPR.