Original sentence: Typical Cepheids pulsate with a period of a few days, and their raidii change by several million kilometers in the process
Edited sentence: A few more have been identified outside the Local Group of galaxies.At this writing, there are over 700 Cepheids known in the Milky Way galaxy, several thousand in the galaxies in the Local Group.They are large, hot stars, 5 - 20 times as massive as the Sun and around 10000 times more luminous.Typical Cepheids pulsate with periods of a few days to months, and their raidii change by several million kilometers (30%) in the process