The Andromeda spiral galaxy was structured less than 3 billion years ago, following a major collision between two galaxies. This is in any case what reveals a recent study based on computer simulations. Our cosmic neighbor would then be younger than our planet.
Andromeda has not finished surprising us. A few days ago, a new technique for measuring the mass of galaxies, applied to our nearest galactic neighbor, revealed that it would eventually be the same size as our galaxy and not two to three times more massive. A study conducted by French and Chinese researchers today reveals that Andromeda was formed following a collision of two galaxies about 3 billion years ago. That’s 1.5 billion years later than our solar system.
Scientists have relied on data collected from previous studies. One of them, spread between 2006 and 2014, showed that Andromeda has an abundance of young blue stars on his record (less than 2 billion years old). They undergo in particular random movements on a large scale. This contrasts with the stars of the Milky Way disk, which are subject only to a simple rotation. In addition, detailed observations made between 2008 and 2014 revealed that the Andromeda halo is populated by gigantic currents of stars. Note that this area is a vast area ten times the size of the galaxy itself.
From these data, the Franco-Chinese collaboration then created a detailed numerical model of the galaxy. To do this, they used the MesoPSL of the Paris Observatory and the IDRIS-GENCI supercomputer of the CNRS, the two most powerful computers available in France.
The researchers were then able to demonstrate that these previous observations could only be explained by a recent collision. Finally, they concluded that between 7 and 10 billion years ago, Andromeda consisted of two galaxies whose trajectories would lead to an inevitable collision. After optimizing the trajectories, they determined that they collided between 1.8 and 3 billion years ago. This is how Andromeda would be born, at least as we know it today. Our solar system was formed almost 4.6 billion years ago.
The researchers were also able to calculate the mass distributions for the two galaxies that merged to form Andromeda: it turns out that the largest galaxy was four times larger than the smallest galaxy. The presence of young blue stars in his record, which has remained unexplained so far, is attributable to a period of intense star formation that took place after the collision.