During the past week, NuSTAR observed RCW 38, a gigantic star-forming region full of young massive stars, each dozens of times heavier than the Sun. These stars blast out powerful winds—streams of hot, ionized gas—at speeds of up to 2000 km/s, releasing energy over their lifetimes comparable to a supernova explosion. Where many such stars are packed together, their winds collide with each other and create powerful shocks, which can accelerate atomic particles to extremely high energies—a possible source of cosmic rays. RCW 38 is especially interesting: it is compact, young (less than a million years old), and apparently free of any supernova explosions. This makes it a rare place to study the effects of stellar winds alone, without other contaminants. Past observations detected X-rays from RCW 38, but were not able to distinguish whether they came from hot gas or accelerated particles. NuSTAR's unique ability to focus high-energy X-rays will help tell the two apart, and the first NuSTAR observation of RCW 38 may be a step toward that answer.

Author: Haruki Kuramoto (PhD Student, University of Osaka, Japan)