AstrophysicsA binary star performed a cosmic striptease
Scientists, notably from UNIGE, believe that Gamma Columbae was born from the merger of two stars, which caused it to lose its envelope, exposing its heart.
Although bright and visible to the naked eye, the star Gamma Columbae, in the constellation of the Dove, located about 900 light years from Earth, was of little interest to scientists. Until an international team recently noticed that its chemical composition on the surface was very different from that of stars of comparable mass. “It corresponds to what we actually expect to find in the central regions of stars three to four times more massive, where nuclear reactions modify the composition of matter”, explains Georges Meynet, full professor at the Department of Astronomy of the Faculty of Sciences of the UNIGE, which therefore sought an explanation.
With his team, supported by the Swiss National Fund, he simulated the evolution of the star by initially imagining it three times more massive than it is and removing its outer envelope. The result of this simulation matches observations, indicating that Gamma Columbae could be the exposed core of an initially more massive star. But why did she lose her envelope?
Since single star models cannot explain this loss, scientists believe that Gamma Columbae originally came from a binary system, that is, it orbited with another star around a center of common gravity. “Our hypothesis is that she swallowed her partner. The phenomenon would have caused significant reactions, and in particular the ejection of its own envelope”, explains Georges Meynet, whose study was published in the journal “Nature Astronomy”.
Explosion predicted in 1 to 2 million years
Given its current composition, Gamma Columbae would be at 90% of its lifespan, estimated at a good ten million years. He would have less than 2 million years to live before exploding. “It is in a fairly short and very rarely observed phase of evolution,” enthuses Georges Meynet, who now has a subject of study to examine in detail the history and future of binary stars.
For now, scientists do not know if these stars are rare or if their detection is not yet optimal. But the discovery of the properties of Gamma Columbae shows that a star that has long been accessible to observation hid a much more complex story than imagined, giving hope that other stars will one day reveal unsuspected properties.