In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

An accretion disk and one of these entities can be used to extract energy from a spinning black hole in the Blandford-Znajek mechanism. The "ballerina skirt" model was used to describe the effects of another one of these entities, whose generating body's rotation influences the shape of the Parker spiral. A star with a particularly strong one of these entities explains bursts from soft gamma repeaters; those stars are a subtype of (*) neutron stars, whose revolution rate decreases over time due to these things. The solar wind is guided by one of these entities, whose reconnection causes solar flares. For 10 points, name these entities, the one of which generated by the earth's core is explained by the dynamo model and influences the direction of compass needles.
Science