Astronomy: Close encounters spawn stellar births

New stars are likely to have been born in the Milky Way as a result of recurrent encounters with neighbouring galaxy Sagittarius, according to a paper published in Nature Astronomy. Analysis of the age of nearby stars indicates that they formed in bursts shortly after a close approach of Sagittarius on at least three separate occasions.

The Sagittarius galaxy is a low-mass satellite of the Milky Way, and it occasionally passes close enough to cause gravitational effects, such as ripples in the distribution of stars.

Tomás Ruiz-Lara and colleagues traced the history of star-forming events by analysing the ages of tens of millions of stars in a 6,500 light-year radius bubble around the Sun. The authors observed that the Milky Way has been producing stars at a constant rate for the second half of its lifetime, but they identified three bursts of enhanced star-forming activity that occurred 5.9, 1.9 and 1 billion years ago. The authors compared the timing of these bursts with simulations of the orbital motion of Sagittarius. This revealed the bursts to be coincident with close approaches between the two galaxies. Galaxies are known to interact with each other gravitationally, and the authors suggest these bursts indicate that Sagittarius has an influence on star formation in the Milky Way. Analyses of the stars in Sagittarius suggest episodes of star formation that are roughly coincidental with those of the Milky Way.