How Milky Way Was Formed: Astronomers Have Created The Most Detailed 'Age Map' Of Our Galaxy

First Posted: Sep 12, 2016 04:50 AM EDT

After identifying the ages of more than 130,000 different stars, Notre Dame Astronomers have finally created the most detailed 'age map' of the Milky Way. This map will not only help researchers understand the formation of our galaxy but also how everything in it grew through the accretion of gases and stars over 13.5 billion years.

Notre Dame Astronomers have produced the map by making use of colors to identify the approximate ages of more than 130,000 stars in the Milky Way's halo. The map was published in Nature Physics along with other findings of Astrophysicist Daniela Carollo, Timothy Beers, Notre Dame Chair, Astro-physics along with assistant professor Vinicius Placco and their colleagues.

The MAP:

The model, developed by theoreticians and astronomers over the past decades, suggests how the Milky Way was formed by merging and accretion of mini-halos. The map shows that the oldest of the Milky Way's stars are at its center and the younger stars are found at much longer distances.

"We didn't previously know much about the age of the most ancient Halo System," Carollo says. "But now we have demonstrated that ancient stars are at the center of the galaxy and the younger stars are found at much longer distances. This is yet another piece of information that we can use to understand the assembly process of the galaxy."

Using data collected from the Sloan Digital Sky Survey, of which Notre Dame is also a partner, the scientists identified more than 130,000 blue horizontal-branch stars that exhibit different colors based on their respective ages. These are the only stars whose age can be determined by studying their color alone.

The stars in the Map show a clear hierarchy, the oldest stars are mostly near the center of the galaxy, while the younger stars further away. "The colors emitted by the stars at a stage of their evolution, are directly linked to the amount of time that star has been alive, so we can study the color to estimate the age," Beers states. "Using the Map, We can visualize how our galaxy was built and can also inspect the stellar debris from the other smaller galaxies that were being destroyed by their interaction with ours during the assembly."

Initial gas clouds containing primordial matter formed the first stars whereas clouds with various masses and gas contents showed a different behaviour: the smaller clouds formed one maybe two generation of stars and merged with other clouds ending in the center of the galaxy. Larger mass clouds lead to the formation of multiple generations of the Young Stars before they had merged, Carollo explains.

At present, we can only use these techniques in our own galaxy and in the dwarf galaxies that surround it. However, the James Webb Space Telescope, that is to be launched in 2018, is expected to collect much more data from farther galaxies. Using the same aging method that Beers' Galactic Archaeology group employed, that data can be used to fill in pieces of the puzzle about our own galaxy's formation, as well as questions about the beginning of our Universe.

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