Thirty years of dramatic temperature elevations of star SAO 244567 have been observed by an international team of astronomers. Currently, the heavenly body is cooling again which translates it into being reborn to an earlier phase of stellar evolution. The event marks the first time that a star has been monitored during the heating and cooling stages of rebirth.
According to University of Leicester's Nicole Reindl, lead author of the study, SAO 244567 is a rare example of a star that allows people to witness stellar evolution in real time. After doubling its temperature, the celestial body ionizes its previously ejected envelope, which is now known as the Stingray Nebula.
Between 1971 and 2002, the surface temperature of SAO 244567, which is 2,700 light years from earth, has surged by about 40,000 degrees Celsius. Observations with Cosmic Origins Spectrograph (COS) on the NASA/ESA Hubble Space Telescope have unveiled that the star has cooled off and expanded.
The rapid heating can be explained if the celestial body has an initial mass that is three to four times the mass of the sun. However, SAO 244567 has a similar mass with the brightest star. With such a low-classified mass, the evolution has longer timescales so the development is mysterious.
In 2014, Reindl and her team have come up with a theory which suggested that a helium-shell flash event, a brief ignition of helium outside the stellar core, has occurred. If indeed the event happened, the star returns to the previous phase of its evolution. Once the heating flash completes, the star should regress its evolution and cool down. The release of nuclear energy by the flash pushes the compact star to expand back to giant dimensions which explains the born again scenario.
The event is not the first time that a flash event occurred. FG Sagittae, which is located in the constellation Sagitta, has experienced the same type of helium flash circumstance. Reindl reasons that there is a need to refine the calculations that will explain the behavior of SAO 244567.
