The Milky Way was born 13 billion years ago

Astrophysics have just discovered the birth date of our galaxy, the Milky Way: it was born 13 billion years ago. Details from Mathilde Fontes, editor-in-chief of the magazineEpsilon.

franceinfo: In what way is this study an important discovery?

Mathilde Fontes: It’s hard to fathom what 13 billion years represent. It’s an astronomical number, literally. For comparison, the entire universe was born 13.8 billion years ago. What does the second day show? Researchers at the Max Planck Institute, Germanyis that our galaxy, the Milky Way, formed only 800 million years after the Big Bang, a very short time after the birth of the universe.

Astrophysicists were counting 3 or 4 billion years after the Big Bang: the Milky Way formed 10 billion years ago. In fact, until then, they had only orders of magnitude. We knew the big story: a cloud of gas condensed into star-forming clumps. This mass of stars is beginning to flip on itself, forming a disk, spiral arms: the galaxy. But we are just beginning to tell his story. Thanks in particular to the data from the Gaia space telescope, which the European Space Agency put into orbit in 2013. This telescope is a cartographer: it measures very precisely the position of stars in the Milky Way.

How was the age of the Milky Way found?

A total of 1.3 billion stars have already been mapped. The next delivery of data from the telescope, scheduled in two months, will reach 1.8 billion. This is the data that astrophysicists used to find the age of the Milky Way. They supplemented them with data from another ground-based telescope, Lamost. Because to determine the age of the stars – and thus the age of the galaxy – it was also necessary to make an analysis of their light by spectroscopy. With Gaia and Lamost, the researchers were finally able to date a sample of 250,000 stars scattered throughout the Milky Way. Thus describing the evolution of the galaxy from the beginning.

What does this discovery tell us in general?

It all started 13 billion years ago, a thick disk of stars formed. And after 2 billion years, a dwarf galaxy was pulled into this disk. She turned around, finally allowing herself to catch her. When it merged with the disk, all the gases mixed and released starbursts. New structures formed: a very thin, highly concentrated disk in and around stars, a halo of stars. Then, 6 billion years later: all the gas in the original cloud was used up. The star formation subsided. Our galaxy is stabilized. This is how our world is shaped. This is how we were born.

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