You measure the velocity of a star at the outer edge of the Milky Way, located a distance of 50,000 lightyears from the galactic center. You infer that the star's complete orbit around the center of the galaxy will take 430 million years. Use Kepler's third law to determine the mass of the Milky Way within 50,000 lightyears. Round your answer to the nearest order of magnitude (1 significant figure).