These relatively nearby stars appear much brighter in the sky than distant quasars, allowing us to collect detailed spectra with real-time variations that reflect the dynamical formation and propagation of structures within their radiatively driven outflows. Obtaining such information is much more difficult for quasars and other very distant, exotic objects. Their research has given astrophysicists insights into the processes that govern formation of disks of gas around rotating stars, spiral wind structures, and collisions between stellar winds. As wind parcels from opposite hemispheres collide over the equator, they form a disk of compressed gas. This WCD model provides a natural explanation for the strong disk emission lines seen from various classes of rapidly rotating hot stars.
Color indicates gas density.
These models ignored gravity darkening, which may inhibit WCDs. However, another aspect of rapid rotation complicates the situation. Colors indicate the stars' surface radiation flux. Their more recent simulations that include gravity darkening and nonradial driving forces now indicate that such additional effects can actually inhibit formation of a WCD and even cause the bright poles to drive a denser wind than the dimmer equator. But the general WCD paradigm is so compelling that it has since been invoked to understand circumstellar matter in a variety of other contexts.