![]() ![]() The waves cause the star to vibrate and brighten in ways that are too subtle to see with the eye, but which can be detected with telescopes such as NASA’s TESS Space Telescope. Some waves propagate only around top layer of a star, while others travel right through the center. This artist’s concept shows how a few individual waves travel through a hypothetical star. You can’t hear them, but sound waves propagate through stars all the time in thousands of different ways. By studying stars of various ages, scientists learn about what will happen to our own Sun as it gets older. Red giants, which are dozens of times as big as the Sun, have lower-frequency waves that can propagate for weeks to months. Any given wave lasts a few days in Sun-like stars, but because new waves crop up all the time, stars are always vibrating. In the Sun, a typical wave completes one cycle in five minutes. The bigger the star, the longer it takes sound waves to travel in its interior. Some waves ripple around the entire circumference of the star, while others dart right through the star’s core. Sunspots form in areas where the Sun’s magnetic field lines weaken the amount of energy brought to the surface, and represent temporarily cooler regions on the surface of the star. These are distinct from the dark spots we know as sunspots on our Sun. In close-up images of our own Sun, we see the effects of waves as localized areas of brightening and dimming. So many waves propagate at once that the overall stellar surface jostles around like Jell-O, but so subtly that the motion would not be visible to the eye. But unlike on these planetary bodies, stellar sound waves are generated continuously by turbulence in the near-surface layers of stars.Ĭonvection-driven waves cause the whole star to expand and contract, in effect ringing the star like a bell. And NASA’s InSight is delving into the interior of Mars by measuring seismic waves there. The Moon also has quakes, measured by instruments that NASA’s Apollo astronauts delivered. Convection, this movement of heat rising and falling, creates waves that bounce around in the star in different ways.Ī similar process happens on Earth: seismic waves, caused by convection, make plates on the planet’s surface move and bump up against one another, eventually leading to earthquakes. Hot gas moves upward to the star’s surface, where it cools off and falls back down - though far more violently and turbulently than in your kitchen. They begin in the star’s convection zone, which is the upper 30 percent of a star’s volume if it is similar to the Sun. Like bubbles rising in a pot of boiling water, sound waves move through a star’s interior because of temperature changes. "We are using seismology to provide an exquisite characterization of the host stars - and hence the planets - we’ve discovered," said W]illiam Chaplin, professor of astrophysics at the University of Birmingham, United Kingdom, who leads the Kepler’s asteroseismology effort for Sun-like stars. And, the more we know about stars, the more we know about planets that orbit them. While both Kepler and TESS are most famous for hunting for planets beyond our solar system (exoplanets), they are also powerful, sensitive tools for detecting stellar vibrations. NASA’s Transiting Exoplanet Survey Satellite (TESS), which launched in April 2018, may observe sound waves in up to one million red giants - the massive, evolved stars that represent what our Sun will look like in about 5 billion years. NASA’s Kepler space telescope, now retired, was a key player in that revolution, delivering observations of waves in tens of thousands of stars after its 2009 launch. Just as earthquakes (or Earth’s seismic waves) tell us about the inside of Earth, stellar waves - resulting in vibrations or "star quakes" - reveal the secret inner workings of stars. The technique is called asteroseismology. By "listening" for stellar sound waves with telescopes, scientists can figure out what stars are made of, how old they are, how big they are and how they contribute to the evolution of our Milky Way galaxy as a whole. Understanding these stellar harmonies represents a revolution in astronomy. These virtuosos don’t just play one "note" at a time, either - our own Sun has thousands of different sound waves bouncing around inside it at any given moment. Small stars have high-pitched voices, like celestial flutes. The biggest stars make the lowest, deepest sounds, like tubas and double basses. We can’t hear it with our ears, but the stars in the sky are performing a concert, one that never stops. ![]()
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