Astrophysicists have just discovered the date of birth of our galaxy, the Milky Way: it was born 13 billion years ago. The details of Mathilde Fontez, editor-in-chief of Epsiloon.
franceinfo: In what way is this study a major discovery?
Mathilde Fontez: It is difficult to realize what 13 billion years represent. It’s an astronomical number, literally. By way of comparison, our entire universe was born 13.8 billion years ago. What two researchers from the Max-Planck Institute in Germany are showing today is that our galaxy, the Milky Way, was formed only 800 million years after the big bang, that is- that is to say very shortly after the birth of the universe.
Astrophysicists were counting on 3 or 4 billion years after the big bang: a formation of the Milky Way 10 billion years ago. In fact, until then, they only had orders of magnitude. We knew the big story: a cloud of gas, which condensed into lumps, which formed stars. This mass of stars which began to turn on itself forming a disc, spiral arms: the galaxy. But we are only just beginning to tell its story. In particular thanks to data from the Gaia space telescope, placed in orbit by the European Space Agency in 2013. This telescope is a cartographer: it very precisely measures 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. It is this data that astrophysicists have used to find the age of the Milky Way. They supplemented them with data from another terrestrial telescope, the Lamost. Because to determine the age of the stars – and therefore the age of the galaxy – it was also necessary to have an analysis of their light, by spectroscopy. With Gaia and the Lamost, the two researchers finally managed to date a sample of 250,000 stars spread throughout the Milky Way. And therefore to describe the evolution of the galaxy, from the beginning.
What does this discovery tell us more generally?
It all started 13 billion years ago, a thick disc of stars formed. And 2 billion years later, a dwarf galaxy was pulled into this disk. She spun around, and finally, she let herself be caught. As it merged with the disc, it mixed all the gas and triggered starbursts. New structures have formed: a very fine disk, very concentrated in stars and around it, a halo of stars. Then, 6 billion years later: all the gas in the original cloud was consumed. Star formation has calmed down. And our galaxy has stabilized. This is how our world was formed. This is how we were born.