*Description*: This illustration depicts one possible explanation for R Aquarii?s semi-periodic outbursts. The peculiar behavior of R. Aquarii suggests that the red giant star in the R Aquarii system may spill some of its mass onto the companion ? a common mechanism proposed for most nova-like outbursts. The mass transfer process may form an accretion disk: a swirling, flattened vortex of hot gasses that spiral down onto the hot companion. The disk may periodically erupt when the companion becomes overloaded with in-falling material. These explosions may happen only periodically when the white dwarf orbits close enough to pull in material from the star?s outer layer. Technical facts about this news release: Back to entire collection [ http://hubblesite.org/newscenter/archive/releases/index/660/ ] Next release [ http://hubblesite.org/newscenter/archive/releases/1990/13/ ] Previous release [ http://hubblesite.org/newscenter/archive/releases/1990/19/ ] *News Release Number:*: STScI-1990-15b