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FAU Erlangen-Nürnberg: Stern loses track

A star in image Taube, about 900 light years from Earth: Gamma Columbae has had a dark past that has now been revealed by an international research team led by Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU). The astronomer Andreas Irrgang from the Astronomical Institute at the Dr. Karl Remeis Observatory Bamberg at FAU is part of an international research team that discovered that the star once formed the heart of a binary star system and lost its envelope when it engulfed its counterpart. As the Friedrich-Alexander University of Erlangen-Nuremberg explains, they recently reported on their results in the renowned journal Nature Astronomy*.

energy from nuclear fusion

It has been known since the late 1930s that stars generate their enormous radiant energy by nuclear fusion of hydrogen into helium at temperatures of many millions of degrees Celsius deep within the star. This fusion takes place in a cyclic process in which carbon, nitrogen and oxygen act as catalysts. This leads to a characteristic enrichment of nitrogen in the core of the star. Because stars are fickle with their nuclear energy supply, they only exist for a few million years before dying in a gigantic explosion known as a supernova. This nuclear evolution is not normally directly observable because the very dense stellar envelopes, a star’s surface layer, shield the hot central fusion reactor. Therefore, predictions of stellar evolution models can only be tested by numerous observations of stellar surfaces.

bare heart

For many years, FAU astronomer Dr. Andreas Irrgang and a colleague from the University of Innsbruck study massive stars by analyzing spectroscopic images of many stars with sophisticated models. Now they have made a unique discovery: the massive star Gamma Columbae in the southern constellation Pigeon has shown deviations in the chemical composition of its surface – unlike what is expected for stars with a similar mass. Together with a leading stellar evolution theorist from the University of Geneva, Irrgang’s scientists found the explanation.

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They concluded that Gamma Columbae, which the researchers suspect once belonged to a binary star system and orbited a common center of gravity with another star, lost its shell when it swallowed its counterpart. It is normal for binary stars to continuously approach each other and lose energy as a result. When the two stars are close to each other, the gravitational waves that cause the energy loss are strong and have a big impact – as should have been the case here. In the case of Gamma Columbae, this process exposed the core, the heart of the star, so to speak. This suggests that Gamma Columbae may be the exposed core of what was originally a much larger star in a former binary system.

Estimated explosion in one to two million years

Based on the determined composition, it can be assumed that Gamma Columbae has reached about 90 percent of its lifespan, which is estimated at a good ten million years. It should have less than two million years to live before exploding. Until then, Gamma Columbae provides a study object that scientists can use to study the past and future of binary stars in detail.

*Original publication: doi.org/10.1038/s41550-022-01809-6

The publications on the paper from the University of Geneva and the Swiss National Science Foundation can be found online.

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