Echoes from asymmetric wormholes and black bounce

The time evolutions of the field perturbations in certain asymmetric wormhole and black bounce backgrounds are investigated. It is found that the echo signals arise only in some wormhole cases. We examine the influences of these wormhole echoes by their mass and charge, as well as the asymmetry of spacetime. The results show that a massive wormhole with smaller charge is easier to observe echo signals. Particularly, the asymmetry of wormhole spacetime causes lower frequency echoes. Besides, analytical results show that the negative regions of effective potentials are enclosed by the black hole horizons for a class of symmetric black bounce metrics. This suggests the stability of these symmetric metrics.