” ‘Put all of those ingredients together, and you get an age of 14.5 billion years, with a residual uncertainty’ . . . plus or minus 800 million years, which means the star could actually be 13.7 billion years old”
Later in the article:
“The Methuselah star, which is just now bloating into a red giant, was probably born in a dwarf galaxy that the nascent Milky Way gobbled up more than 12 billion years ago, researchers said. The star’s long, looping orbit is likely a residue of that dramatic act of cannibalism.”
— leaving the impression that something 13 to 14 billion years old was created roughly 12 billion years ago. Only on close reading will a layman come to the conclusion that the star somehow survived its galaxy being gobbled up (rather than being creatd as a result of that event), and had its orbit affected as a result.
The article also says “The star moves at about 800,000 mph (1.3 million km/h)” but doesn’t say relative to what.
The Milky Way and Andromeda are going to collide and during that collision, not much is going to touch one and other. Space is vast.
When a galaxy is “eaten up” by another galaxy, that means that the two merge, and more or less assume the identity of the larger galaxy. Few, if any, of the stars fall into the larger galaxy’s central black hole, or anything like that. Sort of like mitosis going backward in time.
The 800,000 mph seems to refer to the “proper motion” (as opposed to parallax) of the star, which would be motion with respect to our little solar system. You are correct, it is not at all clear.