ASK Space

GALAXIES

Can galaxies die?

It very much depends on how you define a galaxy being alive! A common definition is that a galaxy is alive if it’s forming new stars, and by that definition, galaxies can - and often do - die. Any galaxy we see that is very red in colour has mostly stopped forming stars - the blue stars that formed with the red ones die off the quickest, leaving the red ones behind.

There are many reasons a galaxy might stop forming stars - maybe it’s out of gas, needed to form new stars. Maybe the gas is there, but simply too hot to be able to cool and collapse down into a star. The end result is the same in both cases: no new stars. On the other hand, you could choose a more lenient definition: if it exists, it’s alive. To die would thus