A team of astronomers has made a once-in-a-lifetime discovery that will help address long-standing mysteries about the development of stars. Keivan Stassun, a member of the Evolutionary Studies Initiative and a Stevenson Professor of Physics and Astronomy, leads the group.
 |
| Artist concept of TESS observing an M dwarf star with orbiting planets. : NASA’s Goddard Space Flight Center |
In 2017, Stassun's team developed a new model that significantly improved the way stars are assessed.
“Being able to combine all of the different types of measurements into one coherent analysis was certainly key to being able to decipher the various unusual characteristics of this star system,” Stassun stated.
The model aids in the prediction of the sorts of planets known as exoplanets that orbit distant stars. It has been used to determine the features of over 100 stars discovered by the TESS satellite telescope, as well as thousands of more. But nothing could have prepared the researchers for what this new binary star system – literally two stars circling each other – may reveal about our cosmos.
According to Stassun, “This type of star is so extremely unusual that, frankly, we would not have thought to go looking for it – nobody has seen one before!”
Stassun described how many key ingredients combine to make this binary star system very rare. Binary star systems are not rare in the universe, but one incredibly rare characteristic of this one is its orientation. The stars eclipse each other when observed from Earth. This enables astronomers to more readily compute essential properties of the two stars, such as mass and brightness.
In addition, stars may change size and brightness in a phenomenon known as pulsing, and studies of these pulsations allow astronomers to investigate the inner workings of stars in the same way that Earth scientists use earthquake vibrations to examine the Earth's underlying structure. There are two forms of unusual stellar pulsing, each of which gives a unique and complementary perspective into star interiors. One of the stars in this binary star system discovered by Stassun's team is a hybrid of both.
“Stars exhibiting either of those pulsating behaviours are quite rare; a star exhibiting hybrid pulsating behavior is even more so,” Stassun said.
Next, this one-of-a-kind star has a high magnetic field, which is unusual for a hybrid pulsating star and might be a critical missing piece in existing models for understanding the early phases of star formation.
“This type of star is so extremely unusual that, frankly, we would not have
thought to go looking for it – nobody has seen one before!”
Finally, according to Stassun, “this is the first time that one of these rare magnetic hybrid pulsating stars has been found that is part of a star cluster and that is moreover a part of an eclipsing binary system. It seems quite unlikely that TESS will discover another star that has all of these attributes together.”
Dax Feliz, a graduate student, also played an important part in this research. He became a fellow in the lab through the Fisk-Vanderbilt Masters-to-PhD Bridge Program.
According to Feliz, “the discovery of this rare eclipsing binary star system provides a fantastic test bed for understanding how stellar binaries evolve over time. As the TESS mission continues observing large patches of sky, star systems like HD 149834 which are located in star clusters can help us further our understanding of stellar evolution.”