Chinese Acad Sci, Inst High Energy Phys, Key Lab Particle Astrophys, Beijing 100049, Peoples R China
; Chinese Acad Sci, Natl Astron Observ, Beijing 100012, Peoples R China
The highly disturbed hot gas in elliptical galaxies, as revealed in many Chandra X-ray images, implies a source of energy in the galactic nucleus. In some elliptical galaxies, faint X-ray "ghost" cavities appear without corresponding radio lobes. It has been suggested that ghost cavities are caused by short-lived activity with a timescale of similar to 10(3) - 10(4) yr, but this is difficult to understand within the popular paradigm of active galactic nuclei. We suggest an episode model for ghost cavities, invoking captures of red giant stars by the black hole located at the center of elliptical galaxies at a typical rate of 10(-5) yr(-1) per galaxy. The accretion of tidally disrupted red giant stars onto the black hole powers activity in a timescale of a few years. The total energy channeled into the jet/outflow during the cooling time of the hot gas is similar to 10(56) ergs, which is the typical work required to form the observed cavities. In this scenario, the faint cavities are produced by the feedback following accretion of the debris of the captured red giant stars onto the black holes. We apply the present model to several elliptical galaxies and find that it can explain the formation of the ghost cavities. This model can be tested in the future by comparisons between radio and X-ray observations.