Milky Way's star-forming disc boundaries identified by Maltese researcher-led study

An international team of astronomers, including researchers from University of Malta, has identified for the first time the outer limit of the Milky Way.

The study, published in Astronomy & Astrophysics, was led by Karl Fiteni, who carried out the work as part of his doctoral research at the University of Malta under the supervision of Joseph Caruana and in collaboration with Victor P. Debattista. 

Astronomers have long struggled to define where the Milky Way ends because its structure does not stop suddenly but gradually fades into space. By analysing the ages of stars, the team was able to determine that most star formation in the galaxy takes place within about 40,000 light-years from its centre.

The researchers looked at how old different stars are at various distances from the middle of the galaxy. They found that stars generally become younger further out, which fits with the idea that galaxies grow from the inside out. 

However, beyond a certain distance, this pattern changes and stars start becoming older again. This shift allowed scientists to identify the boundary where new stars are no longer forming efficiently.

The team combined observations of more than 100,000 stars with computer simulations to confirm their findings. These simulations helped show that the change in star ages marks a real drop in star formation.

The research also explains why stars can still be found beyond this boundary. Instead of forming there, these stars slowly drift outward over time from regions closer to the centre. 

The findings show how new techniques are allowing astronomers to better understand the history of the Milky Way.