A University of Cambridge-led team of astronomers, using chemical elements as a proxy for stellar DNA, has assembled an evolutionary family tree of stars in the solar neighborhood.

Phylogenetic tree of 22 solar twins in the solar neighborhood, created using 17 elemental abundances. Stellar populations are assigned considering the age and the dynamical properties of the stars and are indicated at the right. Branch lengths have units in dex, with the scale indicated at the left bottom. The background image shows the Carina Nebula, a region of massive star formation in the southern skies. Image credit: Jofre et al, doi: 10.1093/mnras/stx075 / ESO / T. Preibisch.

In evolution, organisms are linked together by a pattern of descent with modification as they evolve.

Stars are very different from living organisms, but they still have a history of shared descent as they are formed from gas clouds, and carry that history in their chemical structure.

By applying the same phylogenetic methods that biologists use to trace descent in plants and animals it is possible to explore the evolution of stars.

Writing in the Monthly Notices of the Royal Astronomical Society (arXiv.org preprint), University of Cambridge astronomer Paula Jofre and co-authors describe how they set about creating a phylogenetic tree of life that connects a number of solar neighborhood stars.

In 1859, Charles Darwin published his revolutionary view of life, claiming that all organic beings that have ever lived have descended from one primordial form, the astronomers explained.

One important outcome of Darwins view of descent with modification was the recognition that there is a tree of life or phylogeny that connects all forms of life.

The key assumption in applying a phylogenetic approach is that there is continuity from one generation to the next, with change occurring from ancestral to descendant forms. This assumption is also applicable to stars in galaxies, even if the mechanisms of descent are very different.

The use of algorithms to identify families of stars is a science that is constantly under development, Dr. Jofre added.

Phylogenetic trees add an extra dimension to our endeavors which is why this approach is so special. The branches of the tree serve to inform us about the stars shared history.

Dr. Jofre and her colleagues from the universities of Cambridge and Oxford picked 22 stars, including the Sun, to study.

The oldest star in the sample, HD 220507, is estimated to be 9.8 billion years old, which is twice as old as the Sun. The youngest, HD 96116, is 700 million years old.

The chemical elements were measured from data coming from ground-based high-resolution spectra taken with large telescopes located in the north of Chile.

Once the families were identified using the chemical DNA, their evolution was studied with the help of their ages and kinematical properties obtained from ESAs Hipparcos mission.

Three main stellar populations, i.e. groups of stars sharing a common ancestor, were identified, the astronomers said.

The first one, includes the following stars: the Sun, HD 2071, HD 45184, HD 146233, HD 8406, HD 92719, HD 27063, HD 96116 and HD 134664.

A second stellar population includes the stars: HD 210918, HD 45289 and HD 220507.

A third stellar population appears to be equally independent from the other two populations, and includes the stars HD 78429, HD 208704, HD 20782 and HD 38277.

Finally, six stars HD 28471, HD 96423, HD 71334, HD 222582, HD 88084 and HD 183658 can not be assigned to any population with enough statistical confidence.

We wanted to show that it is possible to apply phylogenetic analyses and tree thinking in the field of Galactic archaeology, the scientists said.

In biology it is commonly said that to study evolution, one essentially analyses trees. Galactic archaeology should be no different, especially now, during its golden ages.

The difference between stars and animals is immense, but they share the property of changing over time, and so both can be analyzed by building trees of their history, added University of Cambridge Professor Robert Foley, co-author of the study.

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Paula Jofr et al. 2017. Cosmic phylogeny: reconstructing the chemical history of the solar neighbourhood with an evolutionary tree. Mon Not R Astron Soc 467 (1): 1140-1153; doi: 10.1093/mnras/stx075

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Astronomers Reconstruct History of Solar Neighborhood with Evolutionary Tree - Sci-News.com