What structure surrounds a protostar and contributes energy via infalling matter?
Answer
An accretion disk
A protostar is almost always surrounded by an accretion disk—a flattened swirl of gas and dust—where material spirals inward, gaining speed before slamming into the surface and converting kinetic energy into thermal energy.

Related Questions
What is the defining process of the protostellar stage?What is the primary mechanism generating the heat and light of a protostar?What process powers mature stars like our Sun once they form?Approximately what core temperature must a Sun-like object reach for hydrogen fusion to ignite?What object results if the initial collapsing mass is too low to start hydrogen fusion?What high-velocity structures are expelled outward from the poles of a protostar?What is the main function of the bipolar outflows during star formation?How does the energy efficiency of nuclear fusion compare to gravitational contraction?What structure surrounds a protostar and contributes energy via infalling matter?Why must observations of active protostars often rely on the infrared spectrum?What event marks the precise moment an object transitions from a protostar to a main-sequence star?