Celebrating the United States' 250th anniversary, NASA released a stunning Hubble portrait of Messier 3, an ancient globular cluster with more than 500,000 stars. The remarkable cluster is helping scientists unravel the Milky Way's past thanks to its rare stars and possible origins in a long ago cosmic merger. Globular clusters are tightly packed, spherical collections of stars bound together by gravity. Unlike younger star groups that continue to evolve, the stars in a globular cluster formed from the same cloud of gas at roughly the same time billions of... [3544 chars]