NASA’s Transiting Exoplanet Survey Satellite hunts for exoplanets, but its sensitive measurements of stellar brightness make it ideal for studying stellar oscillations, an area of research called asteroseismology.
Just below the surfaces of Sun-like stars, 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 — that interact, ultimately driving stable oscillations with periods of a few minutes that produce subtle brightness changes.
Giant stars with masses similar to the Sun’s pulsate much more slowly, and the corresponding brightness changes can be hundreds of times greater.
Oscillations in the Sun were first observed in the 1960s.
Solar-like oscillations were detected in thousands of stars by the Convection, Rotation and planetary Transits (CoRoT) space telescope, which operated from 2006 to 2013.
NASA’s Kepler and K2 missions, which surveyed the sky from 2009 to 2018, found tens of thousands of oscillating giants.
Now NASA’s Transiting Exoplanet Survey Satellite (TESS) extends this number by another 10 times.
“With a sample this large, giants that might occur only 1% of the time become pretty common,” said Dr. Jamie Tayar, an astronomer at the University of Hawaii.
“Now we can start thinking about finding even rarer examples.”
In the new research, the astronomers applied machine learning towards long-cadence TESS photometry data to automatically detect the presence of red giant oscillations in stellar spectra.
They were able to identify a total of 158,505 pulsating red giants.
Next, they found distances for each giant using data from ESA’s Gaia mission, and plotted the masses of these stars across the sky.
Stars more massive than the Sun evolve faster, becoming giants at younger ages.
A fundamental prediction in Galactic astronomy is that younger, higher-mass stars should lie closer to the plane of our Milky Way Galaxy, which is marked by the high density of stars that create the glowing band of the Milky Way in the night sky.
“Our map demonstrates for the first time empirically that this is indeed the case across nearly the whole sky,” said Dr. Daniel Huber, also from the University of Hawaii.
“With the help of Gaia, TESS has now given us tickets to a red giant concert in the sky.”
“Our initial result, using stellar measurements across TESS’ first two years, shows that we can determine the masses and sizes of these oscillating giants with precision that will only improve as TESS goes on,” said Dr. Marc Hon, also from the University of Hawaii.
“What’s really unparalleled here is that TESS’ broad coverage allows us to make these measurements uniformly across almost the entire sky.”
Marc Hon et al. 2021. A ‘Quick Look’ at All-Sky Galactic Archeology with TESS: 158,000 Oscillating Red Giants from the MIT Quick-Look Pipeline. ApJ, in press; arXiv: 2108.01241