Context : Observations with modern instruments such as Herschel reveal that stars form clustered inside filamentary arms of \sim 1 pc length embedded in Giant Molecular Clouds .
On smaller scales ( \sim 1000 au ) , observations of , e.g. , IRAS 16293–2422 show signs of filamentary ‘ bridge ’ structures connecting young protostars in their birth environment .

Aims : We aim to find the origin of bridges associated with deeply embedded protostars , by characterizing their connection to the filamentary structure present on GMC scales and to the formation of protostellar multiples .

Methods : Using the magnetohydrodynamical code ramses , we carry out zoom-in simulations of low-mass star formation starting from Giant-Molecular-Cloud-scales .
We analyze the morphology and dynamics involved in the formation process of a triple system .

Results : Colliding flows of gas in the filamentary arms induce the formation of two protostellar companions at distances of \sim 1000 au from the primary .
After their birth , the stellar companions quickly ( \Delta t \sim 10 kyr ) approach and orbit the primary on eccentric orbits with separations of \sim 100 au .
The colliding flows induce transient structures lasting for up to a few 10 kyr connecting two forming protostellar objects that are kinematically quiescent along the line-of-sight .

Conclusions : Colliding flows compress the gas and trigger the formation of stellar companions via turbulent fragmentation .
Our results suggest that protostellar companions initially form with a wide separation of \sim 1000 au .
Smaller separations ( a \lesssim 100 au ) are a consequence of subsequent migration and capturing .
Associated with the formation phase of the companion , the turbulent environment induces the formation of arc- and bridge-like structures .
These bridges can become kinematically quiescent , when the velocity components of the colliding flows eliminate each other .
However , the gas in bridges still contributes to stellar accretion later .
Our results demonstrate : bridge-like structures are a transient phenomenon of stellar multiple formation .