Our solar system is nestled in one arm of the Milky Way. Our galaxy, 13 billion years old, contains nearly 200 billion stars. To better represent this immense figure, there are on average 100 billion grains of sand in a cubic meter of beach.
In addition to being overpopulated, our Galaxy is huge. Light takes 52,000 years to pass from one opposite to the other. Despite our in-depth knowledge on the subject, several questions still remain unanswered. One of the most important concerns the heart of the Milky Way.
The old heart of the Galaxy was before our eyes
A new study published in “The Astrophysical Journal” claims to have found an ancient core 12.5 billion years old. This discovery is not really a discovery, in the sense that this heart of the galaxy had already been mentioned in studies in the past.
However, this is the first time that this region of our galaxy has been described with such precision. With an estimated age of around 12.5 billion years, the core of the Milky Way has evolved a lot over time. Today it is not at all the same as at the origins of the Universe.
Researchers from Germany’s Max Planck University used ESA’s Gaia satellite to make such an observation. In order to distinguish a star several billion years old from another, they use a now well-known process called metallization.
Reading the past in metals
In other words they look at the number of particles heavier than helium present in the star’s atmosphere. With this data, they are able to hang up a star at a time. If the metal content is low but rising, the star is very young and still forming.
If, on the contrary, the rate is very high, the star is at the peak of its existence. It will soon explode into a supernova. This internal destruction of the star will lead to the release of “metals” into space. The oldest stars in the galaxy therefore have a very low and constantly decreasing rate of metallization.
The “poor old heart” discovered by scientists therefore corresponds to an area of our galaxy where the stars have an extremely low level of metallization. This very ancient region was born more than 12 billion years ago.
Understand the origin of our galaxy, and our Universe
Scientists then succeeded in unraveling the thread of the history of our galaxy. During its “adolescence” 11 billion years ago, it collided with another protogalaxy. This contact, already discovered in 2018, was the last in this category.
Since then, the Milky Way has changed little in shape. The stars continue to be born in places, but most of the points that sparkle at night in our sky date back to this “adolescence”.