Recycling Cassiopeia A . ... Credit Copyright: R. Fesen ( Dartmouth ) and J. Morse ( CASA , U. Colorado), Hubble Heritage Team , NASA Explanation: For billions of years, massive stars in our Milky Way Galaxy have lived spectacular lives. ... In this gorgeous Hubble Space Telescope image of cooling filaments and knots in the Cas A remnant, light from specific elements has been color coded to help astronomers understand the recycling of our galaxy's star stuff . ... NASA Official: Jay Norris. ...