In galaxies similar to our Milky Way Galaxy, a star will explode every 26 years or so.a These explosions, called supernovas, produce gas and dust that expand outward thousands of miles per second. With radio telescopes, these remnants in our galaxy should be visible for a million years. However, only about 7,000 years’ worth of supernova debris are seen.b So, the Milky Way looks young. [See Figure 35.]