When we think of astronomy, we tend to think of light, but sounds can be equally important. Vibrations and waves are key to several astrophysical phenomena and researchers have now constructed a catalog of possible stellar vibrations, or starquakes, which they hope to use to work out what’s going on inside stars.
Graduate researcher Jacqueline Goldstein, together with professors Rich Townsend and Ellen Zweibel of the University of Wisconsin-Madison, developed a software that simulates diverse massive stars and their internal vibrations. Researchers have been able to study these vibrations by looking at small changes in the star's brightness. This field, asteroseismology, has been used to estimate stellar properties but the more we learn about the effect of starquakes, the better we can understand the internal structure of stars.
“A cello sounds like a cello because of its size and shape,” Goldstein said in a statement. “The vibrations of stars also depend on their size and structure.”
The software is called GYRE and plugs into the star-simulating program MESA, both of which are open source. Using this software, Goldstein constructed virtual massive stars (the kind that would end in a supernova) and saw how internal pulsations shake them. She then compared her findings to real observations.
“Since I made my stars, I know what I put inside of them," Goldstein explained. "So when I compare my predicted vibration patterns against observed vibration patterns, if they’re the same, then great, the inside of my stars are like the insides of those real stars. If they’re different, which is usually the case, that gives us information that we need to improve our simulations and test again.”
Asteroseismology is not just about stars. Brightness fluctuations are also caused by an exoplanet passing in front of its star. Many astronomers are keeping an eye on stars to find planets, but they might also find stellar pulsations. Last year, NASA sent its latest planet-hunting telescope TESS to space where it is looking at the closest, brightest 200,000 stars. A key resource to study starquakes.
“What TESS is doing is looking at the entire sky,” added Goldstein. “So we’re going to be able to say for all the stars we can see in our neighborhood whether or not they’re pulsating. If they are, we’ll be able to study their pulsations to learn about what’s happening beneath the surface.”
Goldstein is now adapting the software to work with TESS and use its treasure trove of data to reconstruct the notes in this cosmic symphony.