At the heart of the Stingray Nebula, about 2,700 light-years from Earth, is the small aging star SAO 244567. Astronomers have been observing it for decades and most recently reported seeing a never-before-seen spectacle of stellar rebirth.
From 1971 to 2002, the surface temperature of SAO 244567 rose sharply from 20,000 degrees Celsius to nearly 60,000 degrees Celsius. At the same time, during the same time, the star, initially being four times the size of our Sun, has decreased to 1/4 of its size. Observations of this distant star with the Hubble Space Telescope showed that it began to cool and expand again. In recent years, its surface temperature has dropped to 50,000 degrees Celsius.
Nicole Reindl, an astronomer at the University of Leicester who has observed SAO 244567 for many years, believes that we are witnessing a never-before-seen phenomenon of a "helium burst" that occurs while a low-mass star is in the red giant phase. As part of this event, hydrogen burns out in the core of the star, which leads to an increase in the temperature and density of the core. This process heats up the core so much that it ignites the entire helium supply it contains. As a result of all this, an intense outbreak occurs.
“The amount of fusion energy released from the flare is so enormous that it makes the compact star expand again to gigantic proportions. In fact, there is a rebirth,”says Reindl.
This is not the first time astronomers have found such stars, but in this case, for the first time, scientists became direct witnesses of both phases - heating and cooling. Usually the process of stellar evolution takes several million, or even billions of years. The ability to trace the complete process of evolution over just a few decades only further confirms the fact how dynamically everything can develop in the Universe and how little we actually know about the forces that control these processes.
NIKOLAY KHIZHNYAK