Brainstorm: What stars can tell us about the universe

Neya Thanikachalam, Interactives Editor

When you look up at the night sky, do you ever wonder where all those stars came from? Brainstorm’s Neya Thanikachalam spoke to the experts to find out.

JEFF ANDREWS: Then when you look at a telescope, when you look at the sky, you see these sort of clusters of stars that look roughly like circles on the sky, where you just have a lot of stars together.

NEYA THANIKACHALAM: That was Jeff Andrews, a Northwestern University astrophysicist. He’s doing research on star formation and star motion. But recently he hasn’t been studying those star clusters. Because that tiny little slice of space and those clusters of stars that you’re seeing through the telescope? They don’t really show us the whole picture.

NEYA THANIKACHALAM: Hi everyone, thanks for tuning in! I’m Neya Thanikachalam, and this is Brainstorm, a podcast about all things health, science and tech. Today, we are looking at something out of this world. That’s right, this is an episode about stars. So let’s start with the basics: Where do stars come from? How are they formed? Does the universe have a standard recipe for them?

CULINARY EXPERT AKA CHEF (BENNETT PETERSEN): Combine a heaping cup of hydrogen and a pinch of helium. Then, use the force of gravity to-

NEYA THANIKACHALAM: Wait, no. That doesn’t seem right. Let’s check in with Jeff.

JEFF ANDREWS: When you have enough gas – really it’s mostly hydrogen, but also some helium and other things, but mostly hydrogen gas together — if you have enough of it close enough together it’ll actually what we call self gravitate, which means the gravity of the gas pulls itself together closer and in doing so, you actually start to form a ball right, it becomes a sphere and the very center of that sphere gets hotter and more dense and has a higher pressure and a higher temperature and so it all collapses and at some point you essentially get a spark at the very center. It’s like a flash point where conditions exist, such that you start fusion, and that’s how stars are formed, really.

NEYA THANIKACHALAM: So Jeff just gave us an overview of star formation, but let’s dive a little deeper. Like he said, there are all these conditions that need to be just right for a star to form, and that happens when a cloud of mostly hydrogen gas collapses and gets hotter and creates pressure to start the process of fusion. During fusion, two hydrogen atoms collide into each other to make a helium atom. This process releases a lot of energy and powers stars. In fact, our sun uses this process to produce energy. But, let’s zoom out.

Before, we were only looking at a single star, but scientists think that most stars form in groups. And when we think of groups of stars, we usually picture these spherical, perfect, clusters of stars. Which, in theory, makes sense.

MARCEL AGÜEROS: Well, I should wind up with balls of stars. I start out with a big ball of gas, then I should wind up with balls of stars.

NEYA THANIKACHALAM: That’s Prof. Marcel Agüeros, an associate professor of astronomy at Columbia University. And this explanation of star formation, that ends up with a bunch of perfect, glowing balls in the sky, well, it’s not completely right.

CHEF (BENNETT PETERSEN): You call these stars!? This recipe is bland! Boring! Add more spice! More pizazz!

NEYA THANIKACHALAM: Umm… maybe not that.

EMMA EDMUND: When a mommy star and a daddy star love each other very much…

CHEF: No no no! That is the wrong technique.

NEYA THANIKACHALAM: OK, neither of those were right. But the process of star formation is a little complicated and messy. Marcel and Jeff worked together with other researchers from Columbia University, Pontificia Universidad Católica, the University of Tampa and Western Washington University, and found a different pattern of stars in the sky.

MARCEL AGÜEROS: You start out with the sphere, but then, what happens is that instead of getting these balls that are forming nice spherical grouping[s] of stars you actually wind up with these string-like structures, like filaments, and the star formation takes place sort of in clumps along a string.

NEYA THANIKACHALAM: The researchers looked at a specific stream of stars, called Theia 456. They used three different ways of looking at data to gather information about this stellar stream.

MARCEL AGÜEROS: Ultimately, the really nice thing about this project is that it included these three very different data sets and approaches to build this picture for this structure that was consistent.

NEYA THANIKACHALAM: Researchers used large datasets and the help of AI to pinpoint the stellar stream, and then they used information about the chemical composition of the stars and their brightness to learn more about why these stars were all a part of this one stream. Putting together all this information required a lot of collaboration.

MARCEL AGÜEROS: The fun part about a project like this is really bringing in different people who I know [in] different ways and with whom I like to work to carve out this project that sort of draws on our collective expertise.

NEYA THANIKACHALAM: By combining these different datasets, they learned that all 468 stars in Theia 456 formed together and are moving in the same direction. But, Jeff said there are still a lot more questions that need to be answered.

JEFF ANDREWS: One of the fundamental questions we’re trying to answer is “Were stars born that way? Were they born in long strings and that’s what we see today?” or “Were they all born in sort of these clusters, these spheres, and then they were just sort of shredded over time, they just sort of disperse into streams later.”

NEYA THANIKACHALAM: This is really important to look into because understanding the way that stars form can unlock a lot more information about our galaxy and the universe.

JEFF ANDREWS: If you really want to know what the origin of our sun, our solar system, our planet is, you really want to answer these questions about how our stars formed in the universe.

NEYA THANIKACHALAM: Wow. Those scientists sure are *stars* but now we’re going to rewind. Back to the star formation process. So you know, all this gas and dust is collapsing, and the star is about to form…

But then it doesn’t. That fusion process we talked about, where hydrogen atoms combine? That never happened because something’s a little off with the recipe.

CHEF: I told you to add a cup of hydrogen! This is too little! You’ve ruined the dish!

NEYA THANIKACHALAM: That’s right! Even though gas and dust collapsed to start the process, it wasn’t dense enough to start hydrogen fusion. Instead, what you end up with is called a brown dwarf. But we still don’t completely understand why matter collapses into a brown dwarf instead of getting dense enough to just become a star.

DANIELLA BARDALEZ GAGLIUFFI: I don’t think that we can claim that we’re forming a brown dwarf until it is done. So in that way, I think the formation pathways are the same.

NEYA THANIKACHALAM: That’s Daniella Bardalez Gagliuffi, a Postdoctoral Research Fellow at the American Museum of Natural History. Essentially, a brown dwarf is an almost-star. It’s not massive enough to start burning hydrogen through the process of fusion to release energy, which is what stars are supposed to do. So really, a brown dwarf is in a category of its own.

DANIELLA BARDALEZ GAGLIUFFI: And because brown dwarfs are formed with less mass than required in order to fuse hydrogen in a sustainable fashion, then all they’re releasing is not light that they are making, but is is this leftover energy from the original gravitational collapse. So they will get cooler over time.

NEYA THANIKACHALAM: So brown dwarfs aren’t letting off a lot of light, which means they’re pretty hard for scientists to find. In fact, the light they emit can only be picked up by an infrared telescope. That means we can’t see them if we look up at the sky.

DANIELLA BARDALEZ GAGLIUFFI: With our eyes, we cannot see any brown dwarfs, unfortunately. It’s a very different sky. The infrared sky looks so different from the optical sky.

We use infrared spectra to classify them because they’re brightest in the infrared, as opposed to stars that are brightest in our optical wavelengths, and the spectra changes dramatically from younger brown dwarfs to older brown dwarfs.

NEYA THANIKACHALAM: Daniella studies binary systems, or two objects that were formed together and evolve together, to look into how brown dwarfs are formed.

DANIELLA BARDALEZ GAGLIUFFI: The idea is that binary systems, their system and orbital parameters, like the separation between the two objects or their mass ratio or the eccentricity of their orbit, and also the atmosphere, the composition of the brown dwarfs, mostly, these are all sort of like pieces of a puzzle that together can paint this picture of how they form.

And we’re interested in understanding how brown dwarfs form in general, because nowadays we’re finding a lot of objects that are isolated that are cold enough, but we don’t know if they are very low-mass brown dwarfs or if they are planets that have been ejected from their systems. Because of this, we don’t understand the origin of a lot of these isolated objects. It’s a really interesting question to try to figure out how they form, and understanding how they form also leads to understanding planet formation and brown dwarf formation. How are those processes different? Do they look different in different environments? In the past? In the future, will they look different?

NEYA THANIKACHALAM: Understanding what’s out there in space is complicated, to say the least. And so many different scientists are working on research that tells us more about our universe.

DANIELLA BARDALEZ GAGLIUFFI: The tiny bit of research that I do is a smaller piece in a giant puzzle of trying to understand how our whole universe was formed and in the end, astronomy is that, you know? It’s asking the big questions like “Where do we come from?” and “Is there life there somewhere else?”

NEYA THANIKACHALAM: That’s all for today folks. Thanks for listening. This episode was reported and produced by me, Neya Thanikachalam. Ruby Gibson provided the vocals for the covers of “Twinkle, twinkle little star,” “When you wish upon a star” and “Counting stars.” Thank you Bennett Petersen for voicing our Chef and Emma Edmund for providing additional audio. The audio editor of The Daily Northwestern is Alex Chun, the digital managing editors are Molly Lubbers and Olivia Yarvis, and the editor in chief is Sneha Dey.

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Twitter: @neyachalam