In this article https://arxiv.org/pdf/0809.0907v1.pdf Author analyze energy density of wormhole equal density of string. Black holes don't have such density in event horizon - only if it minimal size black hole made entirely from strings. Maybe real black hole interior core going to have this...
Recently viewed video about wormholes that required negative energy to create it. Suppose hypothetical aliens have discovered this technology. Spaceship enters in first point and exit at second. To prevent spaceship destruction they might have technology to smooth gravitational waves on exit...