Slide 4 of 49

Typical spiral galaxy. At one time, nearly all galaxies in the universe were spirals. However, now, only 5% of all galaxies are spirals. This is an important consideration for the existence of life, since life is only possible in spiral galaxies. Star formation ceases too early in elliptical galaxies, resulting in insufficient production of the heavy elements necessary for life. Likewise, star production is reduced in irregular galaxies, in addition to the problem of unstable stellar interactions, which would be hazardous to planetary orbits.