What happens when 2 young stars with surrounding discs collide in star forming regions? When they encounter, one or both stars start wildly accreting disc material. This translates into spectacular (FU Orionis-type) outbursts. A sort of stellar firework!

Young stars with pre-existing circumstellar discs experience longer and more intense outbursts when subjected to flybys by other stars (compared to stars w/o discs). This is a natural outcome: the more extended and the more massive the discs, the more spectacular the encounter.

Encounters can either be prograde (if the perturber star moves in the same sense as the disc rotates) or retrograde otherwise. In retrograde flybys, both stars experience outbursts; while in prograde flybys, only the secondary star does. So, in short: orbits matter for stellar fireworks.

During outbursts, up to 100% of the accreted material comes from the disc of the other star. Also, the discs can exchange material during the flyby. In other words, the material being captured and eaten by the star is of “alien” nature.

The famous case of FU Orionis is of particular interest since we suspect a flyby occurred in that binary system. Future research will reveal the details of such a stellar encounter.

For more information check the article: Borchert, Price, Pinte & Cuello (2022b).
Paper available here via the Astrophysics Data System.