An international team of astronomers has recently identified a new class of galactic nebulae. Their discovery offers evidence for a fully developed shell of the common shroud system (CE). CE is the common envelope phase of binary star systems.
"Towards the end of their lives, normal stars expand into red giant stars. Since most stars are in binary stars, this affects evolution at the end of their lives. In a closed binary system, the expanding outer portion of a star coalesces as a common shroud around the two stars. However, within this gaseous envelope, the cores of the two stars are practically undisturbed and follow their evolution like a single independent star," explains Stefan Kimeswenger, an astrophysicist at the University of Innsbruck.
The researchers have now published the results of their research in the journal Astronomy & Astrophysics on December 17, 2021 with the short title: YY Hya and its interstellar environment. Many star systems are known to be remnants of such an evolution. Its chemical and physical properties serve as fingerprints. Also, star systems that are just about to develop a common shroud have been discovered due to their specific and high brightness. However, the fully developed CE envelope and its release into interstellar space have so far not been observed in this form.
"These shrouds are critical to our understanding of the evolution of stars in their late phases. In addition, they help us to understand how they enrich interstellar space with heavy elements, which in turn are important for the evolution of planetary systems, such as our own." explained Kimeswenger, of the importance of the newly discovered galactic nebula.
He added an explanation as to why the probability of their discovery was low: "They are too large for the field of view of modern telescopes and at the same time they are very faint. In addition, their lifespan is rather short, at least if you consider the cosmic time scale. Only a few hundred thousand years. "
The starting point for this unique discovery was a group of German-French amateur astronomers. Through hard work they searched historical sky images for unknown objects in archives that have now been digitized and eventually found nebula fragments on photographic plates from the 1980s. The group then contacted international scientific experts, including the Department of Astro and Particle Physics at the University of Innsbruck, experienced in this field. By compiling and combining observations from the past 20 years, derived from the public archives of various telescopes and with data from four different space satellites, the researchers at Innsbruck were able to rule out their first assumption, namely the discovery of planetary nebulae caused by stellar remnants that exploded. dying. The extent of the enormous nebula finally became clear with the help of measurements made by the telescope in Chile. Scientists in the US finally completed this observation with a spectrograph.
“The diameter of the main cloud is 15.6 light-years, almost 1 million times larger than the distance from Earth to the sun and much larger than the distance from our sun to its nearest neighbour. Because the object is located slightly above the Milky Way, this nebula was able to expand largely undisturbed by other clouds in the surrounding gas," Kimeswenger said of the discovery.
By combining all this information, the researchers have succeeded in creating an object model. It consists of a close binary system of a 66,500-degree white dwarf and a normal star with a mass slightly below the Sun. Both orbit each other in just 8 hours 2 minutes and at a distance of only 2.2 solar radii. Due to the small distance, the companion star, with a temperature of only about 4,700 degrees, is heated strongly on the side facing the white dwarf, causing extreme phenomena in the star's spectrum and very regular variations in brightness. Around the two stars is a giant shroud made up of the white dwarf's outer material. With a mass greater than one solar mass, this material is heavier than white dwarfs and their companion stars, and was thrown into space about 500,000 years ago. Another piece of the puzzle related to the discovery of this new class of galactic nebulae has yet to be solved.
"It's even possible that this system is related to the nova observations made by Korean and Chinese astronomers in 1086. However, the position of the historical observations closely matches our object described here," said Kimeswenger.
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