(Written by Christine Pulliam, Smithsonian Astrophysical Observatory, for Science at the Smithsonian, a website featuring highlights of scientific research at the Smithsonian Institution. )
The planet Mercury orbits the Sun once every 88 days. It takes the space station 90 minutes to go around the Earth. But the award for the speediest orbit goes to two stars in the constellation Cancer the Crab, which whirl around each other once every 5.4 minutes at a speed of 400 miles per second (1.5 million mph).
A team of astronomers led by Gijs Roefols of the Harvard-Smithsonian Center for Astrophysics recently examined this pair of stars known to astronomers as RX J0806.3+1527 or, HM Cancri. The two stars are both white dwarfs—the hot cores of dead, sun-like stars. They squeeze as much mass as half our Sun into a globe the size of the Earth. A teaspoon of white dwarf material would weigh about five tons.