I have been thinking about the formation of the galaxy. I can easily understand that old, low-metallicity stars are in the halo, but I'm missing something when it comes to the disk.
If slowly-rotating gas settled into the disk, formed stars, then did the disk at one time consist of Population II stars which have since exploded?
Why did not the same processes happen in both the disk and the halo? That would mean that a lot of Population II halo stars will have exploded and formed plenty of Population I halo stars . . . but without disk dynamics perhaps not many would form. How about the missing Population II disk stars, why are they not still around like the halo clusters?