An artist’s illustration shows a gas giant planet (lower right) closely orbiting its host star (left), with another star in the distance (upper right). The two stars are themselves in orbit with each other.

Chandra data for two of the systems where one star is orbited by a hot Jupiter (HD189733 and WASP-77) and two with neither star orbited by a hot Jupiter (HD46375 and HD109749). In the latter two systems one of the stars hosts a planet that is more distant or has a lower mass than a hot Jupiter. The stars with hot Jupiters are clearly brighter than their companion stars, including a non-detection for the companion in WASP-77. The stars without hot Jupiters have comparable brightness to their companions. This dependence of a star's X-ray brightness on the type of planet it hosts shows that hot Jupiters make their host stars act younger than they really are.