In a seventeenth-century poem, John Donne muses on the “trepidation of the spheres.” In this line, “trepidation” means vibrations, while “spheres” references celestial bodies. In England in the 1600s, many people believed that the cosmos produced divine, musical vibrations, like the hum of violin strings. Four hundred years later, modern astronomy shows that this old poetry isn’t far off the mark.
Stars, in fact, do vibrate like the strings of a violin as they produce sound waves. They also create gravity waves, like water waves in the ocean. Similar to how seismologists measure earthquakes, astronomers use the science of “asteroseismology” to measure the different waves of a star.
Can you hear such ethereal music? Well, I hate to disappoint those seventeenth-century poets, but the answer is no, since sound doesn’t move through empty space. Instead, the various waves make the star’s surface pulse, which causes the star to dim and brighten. Powerful telescopes observe the change in brightness over time. Lots of observation and fancy math reveal the unique patterns of a star’s waves. Since the waves behave predictably when moving through different layers of a star, astronomers can figure out what a star is made of, from its turbulent surface through the bubbling middle and down to a dense core. The waves also reveal information like a star’s mass, age, temperature, and size.Four-hundred years ago, writers like John Donne couldn’t have known that their poetry would parallel modern astronomy. Humanity, though, has always contemplated the heavens, and whether we look with the gaze of a poet, or an astronomer, we always find much at which to marvel.