Compiler/Li Yan
Among the spectacular clouds of gas and dust in the Dragon’s Egg nebula are two massive stars that pose a mystery to astronomers. One of the stars has a magnetic field, like the Sun, while its companion star does not.
Astronomers have now solved the mystery and found that it’s all down to stars killing each other. In the Dragon’s Egg Nebula, a larger star apparently swallowed up a smaller sibling star, mixing the star’s material in the process to create a magnetic field. The research paper has been published in the journal Science.
According to Reuters, Abigail Frost, the first author of the study and an astronomer at the European Southern Observatory in Chile, said, “This merger may be very violent. When two stars merge, material may be thrown out , most likely producing the nebulae we see today.”
Computer simulations had previously predicted that the mixing of stellar material during mergers could generate magnetic fields in the stars born after the mergers.
“Our study is observational conclusive evidence that this is the case,” said Hugues Sana, an astronomer at the University of Leuven in Belgium and senior author of the study.
Researchers used the Very Large Telescope in Chile to conduct observations for nine years.
The Egg Nebula is located in the constellation Norma in the Milky Way, about 3,700 light-years away from Earth. “Dragon Egg” is named because it is located near a larger nebula complex called “Fighting Dragons of Ara”.
The stars in the dragon egg seem to have begun to form 4 million to 6 million years ago. It was originally a three-star system, that is, three stars were born at the same time and were bound by gravity. The two innermost members of the three-star system are a larger star (probably 25 to 30 times as massive as the Sun) and a smaller star (probably 5 to 10 times as massive as the Sun).
Researchers say the more massive star evolved faster than the other, engulfing the smaller star with its outer layers and triggering a merger that ejected the gas and dust that make up the nebula into space. Based on the expansion rate of material in the nebula, the stellar merger occurred approximately 7,500 years ago.
The second star in this binary system did not participate in the violent merger. The mass of the magnetar is about 30 times that of the sun, and the mass of the companion star is about 26.5 times that of the sun. They orbit at a distance 7 to 60 times the distance between the Earth and the Sun. ◇
