UNIVERSITY PARK, Pa. – A new type of pulsating star has been discovered.
Penn State says its researchers were part of an international team that found the star, which has a brightness that oscillates largely over one of its hemispheres.
Researchers say the star is located in a binary star system and its unusual single-sided pulsation is caused by the gravitational pull of its close companion star, distorting the oscillations.
The two companion stars are so close together that they orbit each other every two days. This proximity causes the stars to be distorted into a tear-drop shape by the gravitational pull.
Zhao Guo, a postdoctoral researcher in astronomy and astrophysics at Penn, says stars that pulsate have been known in astronomy for a long time, but this star is special.
“The rhythmic pulsations of the stellar surface occur in young and in old stars, can have long or short periods, a wide range of strengths, and different causes. There is however one thing that, until now, all of these stars had in common: The oscillations were always visible on all sides of the star.”
Penn State says the initial discovery of the unusual behavior of the star was made by citizen scientists who painstakingly inspect the enormous amounts of data that NASA’s Transiting Exoplanet Survey Satellite (TESS) regularly supplies.
After being alerted to the unusual behavior of the pulsating star, the research team observed that the strength of the pulsations depended very strongly on the angle at which the star was observed, and the corresponding orientation of the star within the binary. In addition, the pulsation strength varied with the same periodicity as that of the binary.
"Stars in close binaries can have a teardrop-like shape, so we see different cross-sections of the star at different times," said Guo. “This is how we could be certain that the pulsations were only found on one side of the star, with the tiny fluctuations in brightness always appearing in our observations when the same hemisphere of the star was pointed towards the telescope.”
While this is the first such star to be found where only one side is pulsating, the research team believes that there must be more such stars.
"Beyond its pulsations, there doesn't seem to be anything special about this system, so we expect to find many more hidden in the TESS data," said Saul Rappaport, emeritus professor of physics at the Massachusetts Institute of Technology.