Our Milky Way Galaxy formed by expanding out from the center, possibly having formed inside - out ; suggests analysis of first data from the Gaia-ESO survey

Milky Way Galaxy May Have Formed Inside-Out, Study

Jan 21, 2014 by Sci-News.com

Our Milky Way Galaxy formed by expanding out from the center, suggests analysis of first data from the Gaia-ESO survey – the ground-based extension to the Gaia space mission, launched by the European Space Agency at the end of 2013.

Radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk. Image credit: University of Cambridge.

The astronomers involved with the Gaia-ESO project took detailed observations of stars with a wide range of ages and locations in the Galactic disc to accurately determine their ‘metallicity’: the amount of chemical elements in a star other than hydrogen and helium, the two elements most stars are made from.
Immediately after the Big Bang, the Universe consisted almost entirely of hydrogen and helium, with levels of “contaminant metals” growing over time. Consequently, older stars have fewer elements in their make-up – so have lower metallicity.
“The different chemical elements of which stars are made are created at different rates – some in massive stars which live fast and die young, and others in sun-like stars with more sedate multi-billion-year lifetimes,” said Prof Gerry Gilmore from the University of Cambridge, who is a co-author of the paper submitted to the journal Astronomy and Astrophysics (arXiv.org version).
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.
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