This is Scientific American 60-Second Science. I'm Christopher and Daljata.

When you look up at the Milky Way, you're gazing at the galactic equivalent of a Rome,

a metropolis of stars, with layers upon layers of history, just like the eternal city.

So says the astronomer Hans Walter Ricks.

They work glory days, they work disasters, and all of these things kind of happen in the

life of galaxies, and demicuaries just the one galaxy we can look at star by star,

and so you can kind of see individual episodes in actual detail.

Now Ricks and a colleague at the Max Planck Institute for Astronomy and Germany

have indeed gone star by star, determining the ages of nearly a quarter million stars in the Milky

Way. That work has allowed them to reconstruct some of the major life events in the galaxy's evolution

over its 13 billion years of existence. What it showed is that in the youth and child of the

Milky Way was turbulent, but actually afterwards we've lived an enormously sheltered life

compared to most other galaxies. Gas drizzled in, and the suburbs grew peacefully and sprawled.

The astronomers say that the galaxy's thick disk began to form around 13 billion years ago,

just 800 million years after the Big Bang. Then around 11 billion years ago,

a cataclysmic collision occurred. The Gaia and Cellitis satellite galaxy crashed into the Milky Way.

And just at the same time there was a huge burst of star formation or a large increase of star

formation in our own Milky Way, and that suggests, doesn't prove, that the perturbants that this

infallum satellite created caused a lot of gas that was in our Milky Way to form stars.

The details are in the journal Nature. Now, none of this is a total surprise. People have simulated

the Milky Way's formation before. So I would say really what our work has done is it just shows it

clearly a long suspected picture is coming into focus. In other words, this work lays out a more

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