Fast galactic dynamos and interstellar magnetic bubbles

Large ( > 100 pc) interstellar magnetic bubbles are necessary in the cosmic-ray-driven fast galactic dynamo, as pioneered by Parker in 1992. In a first part, a look is made at the available data on nearby (< 1000 pc) large interstellar magnetic bubbles. Here the magnetic field strengthB in a large shell of densityn around an OB association is found to be a few times greater than that outside in the general interstellar medium, varying typically likeB ~n, as expected for a shocked medium. In a second part, some tests are made of the predictions about interstellar magnetic bubbles made by the theory of a cosmic-ray driven fast galactic dynamo. The bubble tests generally support the idea of a cosmic-ray-driven fast galactic dynamo for the Milky Way.