Astronomers studying the famous Whirlpool Galaxy (M51) have discovered important clues which support theories of how spiral arms can last so long in a galaxy without winding themselves too tightly. M51 is seen face on, so astronomers can see the galaxy's entire structure. A group from the National Radio Astronomy Observatory analyzed clouds containing carbon monoxide molecules and found that they regularly pass through a region of higher density and temperature. This stirs up the gas and prevents it from collapsing into regions of active star formation, and allows the spiral formation of the galaxy to last longer.