how do we tell how old a galaxy is?
In: 3
There’s a lot of variables that go into those calculations. I’ll try to list the simplest ones.
We look at the distance (which is calculated with a complex formula). If a galaxy is 2 billion light-years away, it has to be at least 2 billion years old.
We look at the stars in the galaxy. Thanks to previous research, we know a lot about how stars develop. If the galaxy has stars that take a billion years to evolve, it has to be at least a billion years old.
If a galaxy is 2 billion light-years away, and it’s oldest star is (as we see it) a billion years old, the galaxy is roughly 3 billion years old.
Again, the actual calculations are far more complex, but this is the simplified basis of it.
Latest Answers