Quasinormal modes of a black hole surrounded by quintessence

Using the third-order WKB approximation, we evaluate the quasinormal frequencies of massless scalar field perturbation around a black hole which is surrounded by static and spherically symmetric quintessence. Our result shows that due to the presence of quintessence, the scalar field damps more rapidly. Moreover, we also note that the quintessential state parameter epsilon (the ratio of pressure P-q to the energy density Pq) plays an important role for the quasinormal frequencies. As the state parameter E increases, so does the real part and the absolute value of the imaginary part decreases. This means that the scalar field decays more slowly in the larger c quintessence case.