This arrowhead structure is a classic bowshock pattern produced when high-speed material encounters a slower-speed medium. Young stellar jets were discovered 20 years ago, in part due to visible-light observations of bright patches of nebulosity (called Herbig-Haro objects), which appear to be moving away from associated protostars.

Credit: J. Hester (Arizona State University), the WFPC 2 Investigation Definition Team, and NASA/ESA