Two extremely dense stars in an intimate dance are spinning around each other in just 5.4 minutes -- making them the fastest known stellar partners in the galaxy, astronomers have confirmed. To have such a speedy orbit, the stars must be moving at about 310 miles (500 kilometers) a second, the team calculates. The whirling duo, known as HM Cancri, also has the tightest orbit of any known "binary" star system. Both stars are white dwarfs... The stellar corpses are separated by no more than three times the width of Earth. In such tight quarters, hot gases flow between the...