Stars with a mass similar to the Sun end their lives as white dwarfs. Shortly before, they lose some of their mass. How much ? Astronomers provide an answer thanks to a unique study of a white dwarf at the center of a planetary nebula.
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There are about a thousand of what astronomers call open star clusters in our Milky Way. Each contains several thousand stars that were born at the same time but, depending on their mass, may be in different stages of their life today. That’s why researchers are so interested in it. Open star clusters represent a kind of laboratory in which they can test their theories about stellar evolution.
Stars evolve according to their mass
One of the still unanswered questions is how much mass a star loses. Especially towards the end of his life. Astronomers estimate that stars like our Sun lose about a little less than half of their mass when they evolve into white dwarfs. It’s not nothing. Although it is known that more massive stars lose even more.
However, a very young white dwarf has never been studied before. These stars form at the heart of planetary nebulae, formed from gases ejected by the dying star. But until now, these white dwarfs have been too faint and too distant for astronomers to analyze.
A view of a white dwarf at the center of a planetary nebula
However, researchers at the University of Tübingen (Germany) managed to do this thanks to one of the largest telescopes in the world, the Large Canary Islands Telescope or GranTeCan. In the journal Astronomy & Astrophysics they report how they observed and examined the spectrum of the central star of a planetary nebula in cluster M37. A star now weighs 0.85 solar masses, so it would have lost 70% of its mass over the course of its life. Astronomers also find that the star no longer had any hydrogen on its surface. Enough to take into account the occurrence of an unusual event in the recent past, such as a brief burst of nuclear fusion.