There is one portal in each system with planets. The portal requires 200 Turns to move through and will move you onto the location of the portal in the target system.
Portals can be claimed by other players for 5,000 turns. Once claimed, a player may impose a fee on those who use the portal. Fees range from 0-50%. Similar to planets, a portal can be claimed by another player when the player controlling the portal no longer has any ships in the quadrant.