Growing Galaxies

Scientists have generally thought that the main way galaxies increased in size was by merging, or by bigger galaxies swallowing up smaller ones. A new study suggests that accounts for only a small percentage of the growth. Most of it, instead, comes from a steady accumulation of gas.

Gravity is the key. A large gravity field will tend to bring nearby gas, and other stuff, under its sway. That, in turn, adds mass to the galaxy, further strengthening the gravitational field and allowing the capture of more gas. The incoming gas is the fuel that ignites and supports star formation.

It's a less dramatic, more systematic approach to the building of the cosmos we know. In that sense, it echoes the gradualism versus catastrophism debate in geology. We know Earth has suffered catastrophes that have profoundly changed the planet, just as we know galaxies do in fact merge, but slow processes may have a greater influence on the final product.