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 the 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 be to have the galaxy disappear entirely. The closest we get is if the galaxy were to merge with another galaxy. It would then build a new galaxy with its companion, marking the end of its previous existence. Though it hasn’t disappeared, it’s had all of its pieces folded, like clay, into a new form.
“Any galaxy that is very red in colour has mostly stopped forming stars”
Dr Jillian M. Scudder, department of physics and astronomy, Oberlin College and Conservatory