Stellar bubbles inside planetary nebulae

We calculate the general structures and sizes of bubbles blown by stars located inside planetary nebulae. Such bubbles are likely to be formed by very wide binary companions to the progenitors of planetary nebulae, i.e., orbital separations of ≳ 1000 au, or by passing stars in globular clusters. The bubbles are likely to appear as bright, low-ionization small (10¹⁵-10¹⁷ cm) areas in images of planetary nebulae. We show that the 'blob' of the planetary nebulae 1C4593 might, under favourable physical parameters, be a stellar bubble blown by a very wide red giant companion. We speculate that future high spatial resolution images of planetary nebulae will reveal stellar bubbles in more planetary nebulae.