From the March 2011 issue

Why are all planetary systems and most galaxies disk-shaped?

Jaison Solomon, Trivandrum, India
By | Published: March 28, 2011 | Last updated on May 18, 2023
Face-on spiral galaxy NGC 3982. NASA/ESA/the Hubble Heritage Team (STScI/AURA)

The force of gravity makes some objects, such as the Sun, spherical. Spin plus gravity equals a rotating disk with a vertical thickness much less than its radius.