Asteroseismology allows scientists to explore stars with sound. It can help them figure out what a star is burning and even help pin down the age of stars!
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Sources:
https://www.scientificamerican.com/article/making-sound-waves/
https://www.ucl.ac.uk/EarthSci/people/lidunka/GEOL2014/Geophysics4%20-%20Seismic%20waves/SEISMOLOGY%20.htm
https://exoplanets.nasa.gov/news/1516/symphony-of-stars-the-science-of-stellar-sound-waves/
https://arxiv.org/abs/0811.2908
https://arxiv.org/abs/1103.5805
https://www.scientificamerican.com/article/how-do-scientists-determi/
http://www.ucolick.org/~bolte/AY4_00/week7/cluster_ages.html
https://arxiv.org/abs/1708.00259
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https://www.nasa.gov/feature/goddard/2017/esa-nasa-s-soho-reveals-rapidly-rotating-solar-core
Images:
https://hubblesite.org/contents/media/images/2020/15/4667-Image?page=5&filterUUID=4c394bbb-b21e-43ab-a160-2a4521d70243
https://svs.gsfc.nasa.gov/12729
https://en.wikipedia.org/wiki/File:Structure_of_Stars_(artist%E2%80%99s_impression).jpg
https://exoplanets.nasa.gov/resources/2206/life-and-death-of-a-planetary-system/
https://svs.gsfc.nasa.gov/12292
https://exoplanets.nasa.gov/resources/1002/kepler-beauty-shot/
https://hubblesite.org/contents/media/images/2021/08/4805-Image
https://hubblesite.org/contents/media/images/2020/56/4762-Image?page=3&filterUUID=4c394bbb-b21e-43ab-a160-2a4521d70243
https://svs.gsfc.nasa.gov/13648
Thumbnail: https://svs.gsfc.nasa.gov/13011
In a sense, stars are the fundamental building blocks of the universe. I mean, galaxies are made of stars, planetary systems form around stars, and virtually every atom that isn’t hydrogen or helium was born inside a star. Given all that, it’s not surprising that astronomers
00:19:want to know as much as possible about these objects. But that is easier said than done. There’s only one star scientists can study in detail: our Sun. And, even then, we can only look at it from the outside. Fortunately, astronomers have devised a clever way
01:34:to peek inside stars without actually going there. It’s called asteroseismology, and it takes advantage of the last sense you might expect: sound. Now we often think of sound as something that is heard. But audible sound is just a special case of a more general phenomenon: vibration.
01:51:So, a birdsong isn’t that different from something like an earthquake. One makes vibrations in the air, the other in the earth under our feet. But, in both cases, we can get information about something we cannot see.
01:03:Like, we might know a singing bird is outside the window, even if the curtains are closed. And, while earthquakes happen deep underground, we can feel those effects on the surface. Scientists have taken that one step further with the field of seismology.
01:17:By measuring how earthquake vibrations bounce around inside the planet, they’ve been able to figure out the Earth’s internal structure without ever actually seeing it. Which sounds exactly like what astronomers are looking for in studying stars!
02:30:There’s only one catch, uh, in space, no one can hear you scream, or, you know, hear anything at all. Because space is a vacuum, and there’s no medium for sound waves or any other vibrational waves to travel through. Fortunately, stars make it possible to almost “see” the sound inside them,
02:49:because movement on a star’s surface reflects what’s going on inside it. A key process here is convection, where pockets of material inside a star heat up, become less dense, and rise. When they reach the surface, they lose their heat to space in the form of light.
02:05:Then, as they cool and get denser, they sink down again, making way for the next pocket of rising gas in an endless cycle. This circular motion creates vibrations that ripple across the surface of the star, or, as we might call it, sound.
02:18:And these sound waves cause tiny changes in how the surface emits light, creating little flickers that astronomers can observe. One way researchers have put asteroseismology to work is figuring out what a star is burning. For most of their life, stars fuse hydrogen into helium in their core.
03:36:Then, after that hydrogen is exhausted, they puff up to become red giants. During the red giant phase, they create energy in two ways. First, they burn hydrogen in a shell outside the core. Then, they burn the helium that’s built up inside the core.
03:50:Distinguishing the hydrogen-burning and helium-burning phases from the outside has generally been really difficult, because if you just look at the stars, there’s not much of an obvious difference. But here’s the thing: The helium core is much denser than the shell of hydrogen
03:04:around it. And density has a huge effect on vibrations. So, if the red giant hasn’t started burning its helium core yet, we’ll see different vibrations on the star’s surface. In a 2011 paper, researchers were able to use NASA’s Kepler Space Telescope
03:18:to identify those different seismic waves in around 400 nearby stars, and classify them as either helium-burning or hydrogen-burning. And so now, being able to separate these phases of a star’s life will help astronomers understand what other properties are different in the two groups,
04:34:and what else changes in a red giant over the course of its life. Beyond that, asteroseismology is also helping pin down the age of stars in general. Knowing a random, individual star’s age can answer all kinds of questions,
04:47:like knowing whether it’s been around long enough to have habitable planets. But traditionally, it’s been almost impossible to do. You can usually date a cluster of stars by plotting out their masses and temperatures, and comparing those to other star clusters and models.
04:01:But that doesn’t work for a single, lone star. There’s just not enough data, and although there are some trends, a star looks about the same for virtually its entire life. Except in 2008, a pair of astronomers proposed a way scientists might one day be able to overcome that.
04:17:See, as they age, stars undergo changes in size, density, temperature, and composition, depending on what elements they’re burning, fusing together, and also some other stuff. Those changes can affect a star’s internal structure, which, in turn, affects the way vibrations travel through the star.
05:34:So, if astronomers could study the seismology of a group of stars whose ages they do know, such as those in a star cluster, they could calibrate a model linking seismic activity and age. Then, they could use that model to study some random star, and calculate its age to within 10-20%;
05:52:a huge improvement over the 35-40% margin we have now. That would open the door to all kinds of studies, including how star systems have evolved, how stars change as they age, and of course, whether they could have any exoplanets that could support life.
05:07:Asteroseismology illustrates how clever astronomers have to get when they can’t reach out and touch what they want to study. It’s a good reminder that, in science, even seemingly-random details like the bubbling of a star’s surface
05:20:can be the gateway to a deeper understanding of what’s really going on. Thanks for watching this episode of SciShow Space! If you want to learn more about stars, we recommend watching this episode about how the first stars changed the universe, and not just because they were bright.
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