TESS Tunes into an All-sky ‘Symphony’ of Red Giants

  • Released Wednesday, August 4, 2021
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This visualization shows the new sample of oscillating red giant stars (colored dots) discovered by NASA’s Transiting Exoplanet Survey Satellite. The colors map to each 24-by-96-degree swath of the sky observed during the mission's first two years. The view then changes to show the positions of these stars within our galaxy, based on distances determined by ESA’s (the European Space Agency’s) Gaia mission. The scale shows distances in kiloparsecs, each equal to 3,260 light-years, and extends nearly 20,000 light-years from the Sun.

Credit: Kristin Riebe, Leibniz Institute for Astrophysics Potsdam

Using observations from NASA’s Transiting Exoplanet Survey Satellite (TESS), astronomers have identified an unprecedented all-sky collection of pulsating red giant stars that will aid in mapping the structure of our galaxy.

Sound waves traveling through any object – a guitar string, an organ pipe, or the interiors of Earth and the Sun – can reflect and interact, reinforcing some waves and canceling out others. This can result in orderly motion called standing waves, which create the tones in musical instruments.

Just below the surfaces of stars like the Sun, hot gas rises, cools, and then sinks, where it heats up again, much like a pan of boiling water on a hot stove. This motion produces waves of changing pressure – sound waves. Their interaction drives stable oscillations with periods of a few minutes that produce subtle brightness changes. For the Sun, these variations amount to a few parts per million. Giant stars with masses similar to the Sun’s pulsate much more slowly, and the corresponding brightness changes can be hundreds of times greater.

The physical differences between a cello and a violin produce their distinctive voices. Similarly, the stellar oscillations astronomers observe depend on each star’s interior structure, mass, and size. Studying them can help determine fundamental properties for large numbers of stars with accuracies not achievable in any other way.

Using TESS data for some 24 million stars, a team of astronomers led by Marc Hon at the University of Hawaii developed an AI system to identify 158,505 pulsating giants across the sky.

Listen to the rhythms of three red giants in the constellation Draco, as determined by brightness measurements from NASA’s Transiting Exoplanet Survey Satellite. To produce audible tones, astronomers multiplied the oscillation frequencies of the stars by 3 million times. It’s clear that larger stars produce longer, deeper pulsations than smaller ones.

Credit: NASA/MIT/TESS and Ethan Kruse (USRA), M. Hon et al., 2021

The bright red giant Edasich in the constellation Draco is about 12 times larger and 1.8 times the mass of our Sun. Edasich oscillates three times a day, brightening and fading slightly as it does. For comparison, the Sun pulsates about every five minutes. Left: The star’s changing brightness as measured by NASA’s Transiting Exoplanet Survey Satellite. Right: An illustration of the star and its varying brightness.

Credit: NASA’s Goddard Space Flight Center/Chris Smith (KBRwyle)

NASA’s Transiting Exoplanet Survey Satellite (TESS) imaged about 75% of the sky during its two-year-long primary mission. This plot dissolves between the TESS sky map and a “mass map” constructed by combining TESS measurements of 158,000 oscillating red giant stars with their distances, established by ESA’s (the European Space Agency’s) Gaia mission. The prominent band in both images is the Milky Way, which marks the central plane of our galaxy. In the mass map, green, yellow, orange, and red show where giant stars average more than 1.4 times the Sun’s mass. Such stars evolve faster than the Sun, becoming giants at younger ages. The close correspondence of higher-mass giants with the plane of the Milky Way, which contains our galaxy's spiral arms, demonstrates that it contains many young stars. Credit: NASA/MIT/TESS and Ethan Kruse (USRA), M. Hon et al., 2021

NASA’s Transiting Exoplanet Survey Satellite (TESS) imaged about 75% of the sky during its two-year-long primary mission. This plot dissolves between the TESS sky map and a “mass map” constructed by combining TESS measurements of 158,000 oscillating red giant stars with their distances, established by ESA’s (the European Space Agency’s) Gaia mission. The prominent band in both images is the Milky Way, which marks the central plane of our galaxy. In the mass map, green, yellow, orange, and red show where giant stars average more than 1.4 times the Sun’s mass. Such stars evolve faster than the Sun, becoming giants at younger ages. The close correspondence of higher-mass giants with the plane of the Milky Way, which contains our galaxy's spiral arms, demonstrates that it contains many young stars.

Credit: NASA/MIT/TESS and Ethan Kruse (USRA), M. Hon et al., 2021

Red giant stars near and far sweep across the sky in this illustration. Measurements from NASA’s Transiting Exoplanet Survey Satellite have identified more than 158,000 pulsating red giants across nearly the entire sky. Such discoveries hold great potential for exploring the detailed structure of our home galaxy. Credit: NASA’s Goddard Space Flight Center/Chris Smith (KBRwyle)

Red giant stars near and far sweep across the sky in this illustration. Measurements from NASA’s Transiting Exoplanet Survey Satellite have identified more than 158,000 pulsating red giants across nearly the entire sky. Such discoveries hold great potential for exploring the detailed structure of our home galaxy.

Credit: NASA’s Goddard Space Flight Center/Chris Smith (KBRwyle)

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This page was originally published on Wednesday, August 4, 2021.
This page was last updated on Wednesday, May 3, 2023 at 1:44 PM EDT.