In 1572, Danish astronomer Tycho Brahe observed and studied an exploding star that would later be named after him. NASA's Chandra X-Ray Observatory shows that the Tycho's Supernova remnant is an expanding bubble of debris which is inside a larger bubble of high-energy electrons. Astronomers think that remnants like this could be a source of cosmic rays; high-energy nuclei found throughout the galaxy which constantly bombard the Earth.