translated from Spanish: How do the stars of the Universe age?

A CONICET researcher, in collaboration with colleagues from Italy and England, was able to verify that there are some stars in the universe that age more slowly than previously believed for half a century. The findings, published yesterday in Nature Astronomy, change the understanding of what the aging of these stars is like and postulate that, in some cases, it can take about twice as long as it results from standard models.

Images of two star clusters (M3 and M13) located in the constellations of Canes Venatici and Hercules.

The vast majority of the stars in the Universe (about 98%, including our Sun) will end their lives as white dwarfs, that is, the final stage of their evolution in which they become increasingly colder and less luminous, gradually fading until dark. As the rate at which this occurs is the same for all of them, they are considered “cosmic clocks” useful for inferring ages from other objects in our galaxy and from nearby stellar populations. However, experts from the University of Bologna, the National Institute of Astrophysics – both in Italy – The John Moores University of Liverpool in England and CONICET researcher Leandro Althaus, from the Institute of Astrophysics of La Plata (IALP, CONICET-UNLP), reported that this is not always the case. Their study was based on deep observations made with the Hubble Space Telescope – a joint project of NASA and the European Space Agency (ESA) – on two globular clusters of stars, called M3 and M13, located 33,000 and 25,000 light-years from Earth, respectively, in the constellations of Canes Venatici and Hércules.Se it is a “perfect natural laboratory”, as Althaus writes, because they are “almost twin” systems: they share physical properties such as age, total mass and metal content, i.e. their general composition; and the fact that the stars that compose them were born at the same time. 

Leandro Althaus.

But, contrary to what one might expect, the observations reflected that the white dwarf population in M13 is much more numerous than in M3, even though it globally contains fewer stars, suggesting that most white dwarfs in M13 age more slowly, causing them to remain shiny and visible longer than in M3. where white dwarfs age at the expected rate. As explained by the Argentine researcher through the CONICET website, “what is traditionally accepted is that white dwarfs lack the possibility of producing energy, for example, by generating thermonuclear reactions stable over time, because when they reached that stage they already consumed all the nuclear fuel.” So, as a consequence, its aging results from a simple cooling process. In that sense, the relevance of this study is that it alters that concept and contradicts the widely accepted view: “We found evidence that there are white dwarfs that retain residual nuclear burning, that is, nuclear reactions on their surface, so they maintain an energy source similar to that used by the Sun to transform hydrogen into helium. This remnant of energy is what causes them to grow much more slowly. If in a typical white dwarf that we observe in clusters the process takes about 80 million years, in these it can last up to about 150 million years.” What’s more, the discovery has direct consequences on the methods by which astronomers measure the age of stars in the Milky Way and nearby stellar populations. According to the team, if this new scenario is considered, the estimates made based on the hitherto accepted model could be inaccurate by up to a billion years.” These objects are used as cosmic clocks to determine ages, but also as natural laboratories for the verification of different physical theories, so that our finding can change the conclusions about physical processes that go beyond stellar astrophysics,” Althaus concluded.

Original source in Spanish

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