Spinstars: the first polluters of the Universe?


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Simulation of the formation of the first stars showing fast rotation (Image credits: A. Stacy, University of Texas; figure from Stacy et al, 2011, MNRAS)

Simulation of the formation of the first stars showing fast rotation (Image credit: A. Stacy, University of Texas; figure from Stacy et al, 2011, MNRAS)

Posted on 27 April 2011

Spinstars: the first polluters of the Universe?

Astrophysicists find imprints of fast rotating massive stars in the bulge of our galaxy

From the analysis of the chemical composition of some of the oldest stars in our Galaxy, an international team of astronomers, including Dr Raphael Hirschi of Keele University, presents new clues on the nature of the first stellar generations in our Universe.

The findings will be published in Nature on April 28, 2011.

Soon after the Big Bang, the composition of the Universe was much simpler than at present as it was made of essentially only hydrogen and helium. The chemical enrichment of the Universe with other elements had to wait around 300 million years until the fireworks started with the death of the first generations of massive stars, polluting the primordial gas with new chemical elements, which were later incorporated in the next generations of stars.

Dr Hirschi, of Keele’s Astrophysics group, said: “Massive stars live fast and furious, and hence the first generations of massive stars in the Universe are already dead. However, their chemical imprints, like fingerprints, can be still found today in the oldest stars in our Galaxy.”

These fossil records are thus the witnesses of the nature of the first stellar generations to pollute our Universe.

Using data from the European South Observatory’s Very Large Telescope (VLT), the astronomers reanalysed spectra of a group of very old stars in the Galactic Bulge. These stars are so old that only very massive, short-living stars with masses larger than around ten times the mass of our Sun should have had time to die and to pollute the gas from which these fossil records then formed. As expected, the chemical composition of the observed stars showed elements typical for enrichment by massive stars. However, the new analysis unexpectedly also revealed elements usually thought to be produced only by stars of smaller masses. Fast-rotating massive stars on the other hand would succeed in manufacturing these elements themselves.

“We think that the first generations of massive stars were very fast rotators – that’s why we called them spinstars,” said Dr Cristina Chiappini, of Germany’s Leibniz-Institut für Astrophysik Potsdam, who led the study.

Team member Urs Frischknecht, a PhD student at Basel University co-supervised by Dr Hirschi, is already working on extending the stellar simulations in order to further test the proposed scenario.

The impact of having had an early generation of spinstars in the Universe is manifold. Fast rotation also affects other properties of a star, such as its colour, its lifetime and its luminosity. The existence of spinstars would therefore also have strongly influenced the properties and appearance of the first galaxies which were formed in the Universe. The existence of spinstars is now also supported by recent hydrodynamic simulations of the formation of the first stars by an independent research group.

ENDS

High resolution image available from http://www.aip.de/en/press-and-public-outreach/figure-pr-chiappini/view: Simulation of the formation of the first stars showing fast rotation (Image credits: A. Stacy, University of Texas; figure from Stacy et al, 2011, MNRAS)

Further information: Original publication: Chiappini et al., Imprints of fast-rotating massive stars in the Galactic Bulge, to be published in Nature, 2011. (DOI: 10.1038/nature10000, publication date: April 28, 2011)

Scientific Contact:

Dr Raphael Hirschi, Keele University – 01782 733324 or r.hirschi@epsam.keele.ac.uk

Press Contact:

Hannah Hiles, Media and Communications Officer, Keele University – 01782 733857 or h.e.hiles@kfm.keele.ac.uk


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