Our Milky Way's halo of hot gas is warmer to the "south" than the "north" because of an internal combustion engine-like effect that is compressing the gas like a piston, a new study has found. Computer simulations reveal that the Large Magellanic Cloud—a satellite galaxy below, or on the south side, of our own—attracts the Milky Way, causing gas in the southern half of the halo to compress and heat up.