Two new molecular structures associated with the last eruption of Eta Carina discovered


Figure: image of the Eta Carina system and the Homunculus Nebula, seen by the Hubble Space Telescope. NASA/ESA/Hubble/N.Smith (University of Arizona)/J.Morse (BoldlyGo Institute).


Researchers from the Centro de Astrobiología (CAB, CSIC-INTA) have discovered two new structures in the heart of Eta Carina, a large-mass binary system located 7500 light-years from Earth. These structures, which show an unusual chemical composition, were formed in the late nineteenth century and their discovery has been made possible by the ALMA Observatory.


Eta Carina is an evolved binary star, very luminous and about to exploit as a supernova. This star has captivated astronomers since it suffered two gigantic eruptions in the 19th century, the last of which was in 1890. During these events colossal amounts of dust and gas were expelled, more than 20 times the mass of our Sun, which resulted in the formation of a spectacular Nebula, known as the Homunculus Nebula (Little Man, in Latin). The expelled material, rich in heavy chemical elements, is the perfect environment for the appearance of organic molecules, carbon-based molecules and which are considered as the bricks of life. In this sense, recent observations in the nebula environment had found evidence of molecular gas, although without determining its specific location. Until now, only the distribution of carbon monoxide (CO) in a lumpy ring surrounding the man's waist was known.

Thanks to the ALMA (Atacama Large Millimeter/submillimeter Array) telescope, the molecular material around Eta Carina has been able to study in unprecedented detail. Researchers from the Centro de Astrobiología, using high angular resolution observations from alma archive have managed to discover two new structures in the innermost region of Eta Carina, which originated in the eruption of 1890. The results of this research are published today in the journal Monthly Notices of the Royal Astronomical Society.

Firstly, they discovered a small structure composed of gas and dust, located in the heart of the Little Man. This structure, dubbed Peanut by researchers, was created by material expelled during the eruption and moves away from the star through the turbulent region where the stellar winds of the binary system collide. Secondly, the researchers also found several compact structures that, as projectiles, were moving away at speeds of up to 60 km/s, surely ejected by the nitrogen-rich main star.

What caught the researchers' attention was the unusual chemical composition of these new structures. "In contrast to the outer ring, in Peanut we only detect the HCO+ molecule (known as catid formyl), and we find no indication of CO, which is quite disconcerting considering that carbon monoxide is one of the most abundant molecules in the universe," explains Ricardo Rizzo, researcher at the Centro de Astrobiología and co-author of the study. "This situation is difficult to explain using standard chemical models, so future observations are needed to solve this mystery," he adds. In addition, projectiles are composed only of HCN, hydrocyan acid, indicating that they are material from inside the star that has been enriched in nitrogen.

The Eta Carina system and its environment are one of the few astrophysical scenarios where you can witness the formation of molecules in near real time. "The detected molecules have formed in less than 200 years, a very brief time on the scale of cosmic processes, which can last thousands (or even millions) of years," says Rizzo.

"Studying the molecular gas associated with very massive stars allows us to know what the chemical evolution of these objects has been like, and provides clues to understand the mechanisms that trigger eruptions as violent as those of Eta Carina," says Cristóbal Bordiú, co-author of this study, which is also part of his doctoral thesis.

Massive stars control galactic evolution, altering the shape and composition of galaxies like the Milky Way. Understanding how molecules form in the environment of massive stars has important astrobiological implications, as it helps us understand the chemical enrichment of the early universe.


Fuente: UCC-CAB

Fecha: 2019-10-18


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