  Substellar objects, like planets and brown dwarfs orbiting stars, are
by-products of the star formation process. The evolution of their host stars
may have an enourmous impact on these small companions. Vice versa a planet
might also influence stellar evolution as has recently been argued.
  Here we report the discovery of a 8-23 Jupiter-mass substellar object
orbiting the hot subdwarf HD 149382 in 2.391 days at a distance of only about
five solar radii. Obviously the companion must have survived engulfment in the
red-giant envelope. Moreover, the substellar companion has triggered envelope
ejection and enabled the sdB star to form. Hot subdwarf stars have been
identified as the sources of the unexpected ultravoilet emission in elliptical
galaxies, but the formation of these stars is not fully understood. Being the
brightest star of its class, HD 149382 offers the best conditions to detect the
substellar companion. Hence, undisclosed substellar companions offer a natural
solution for the long-standing formation problem of apparently single hot
subdwarf stars. Planets and brown dwarfs may therefore alter the evolution of
old stellar populations and may also significantly affect the UV-emission of
elliptical galaxies.
