Our galaxy may have formed 'inside-out'

In a major breakthrough, astronomers have figured out that our galaxy - the Milky Way - grew from the inside-out.

Research suggests that stars in the inner regions of the Galactic disc - the vast collection of giant gas clouds and billions of stars that give our galaxy its 'flying saucer' shape - were the first to form.

Using data from the Gaia-ESO project - a public spectroscopic survey - astronomers determined how rapidly different parts of the Milky Way were formedm, said a press release from University of Cambridge.

Massive stars, which have short lives and die as 'core-collapse supernovae', produce huge amounts of magnesium during their explosive death throes.

"This catastrophic event can form a neutron star or a black hole, and even trigger the formation of new stars," said professor Gerry Gilmore, lead investigator on the Gaia-ESO Project.

The team found that older, 'metal-poor' stars inside the Solar Circle - the orbit of our sun around the centre of the Milky Way - are far more likely to have high levels of magnesium.

The higher level of the element inside the Solar Circle suggests this area contained more stars that 'lived fast and die young' in the past, said the study published online at the astronomical database Astro-ph.

The stars that lie in the outer regions of the Galactic disc - outside the Solar Circle - are predominantly younger, both 'metal-rich' and 'metal-poor', and have surprisingly low magnesium levels compared to their metallicity, it added.

"We have been able to shed new light on the timescale of chemical enrichment across the Milky Way disc, showing that outer regions of the disc take a much longer time to form," said Maria Bergemann from Cambridge's Institute of Astronomy.

"This supports theoretical models for the formation of disc galaxies in the context of Cold Dark Matter cosmology, which predict that galaxy discs grow inside-out," Bergemann added.