Here's why:
* Determining galaxy ages is challenging: Unlike stars, galaxies don't have a single "birth" moment. They form gradually over billions of years through mergers and accretion.
* Limited observational data: We can study the ages of stars within galaxies, but it's difficult to get a complete picture of the galaxy's formation history.
* Differences in star formation: Even if we could pinpoint the age of the oldest stars in each galaxy, it doesn't necessarily mean the whole galaxy formed at that time.
What we do know:
* Both galaxies are very old: The Milky Way and Andromeda are both thought to be around 13 billion years old, meaning they formed shortly after the Big Bang.
* Similar formation processes: While there are differences in their shapes and sizes, both galaxies likely formed through similar processes of gas cloud collapse and star formation.
In conclusion: It's more accurate to say that the Milky Way and Andromeda are about the same age, with both being ancient structures in the universe. We don't have enough evidence to confidently state which one is older.
