Quote:
Originally Posted by marc4darkskies
I'm not a glob man but this is lovely M&T! The stretched version has my vote. I've always wondered why they call them stragglers?  |
Thanks Marcus!
Blue stragglers: If a cluster forms out of fresh new gas then at that moment of creation (ten billion years in the past) there will be a main sequence of stars, with a very small number of brilliant hyper-luminous blue O, a small number of B, etc etc, and lots and lots of F, G, K, and M.
A million years later, the O's will be all gone, as supernovas. A bit later still, the B's will go, then the A's will run out of hydrogen in the core, swell up, becoming hyperluminous but cooler, as they move into the giant branch.
With the passage of billions of years, some of the F's and G's will also run out of hydrogen in the core, just as our sun will in another 5 billion years, and swell up, becoming hyperluminous, as red giants. There are indeed quite a lot of red giants in the image!
But the key thing is that with the passage of time, more and more stars, in OBAFGKM order, peel off the main sequence, swelling up, becoming more luminous, and entering the giant branch. The "kink point", or point of peel-off, can be easily picked, and clever people can say, "Oh, the kink point is at F or G, so the cluster is 5 or 10 billion years old", etc, etc, etc.
BUT
In the actual image, there are all these hyperluminous OB stars that just should not be there. They are still on the main sequence, ten billion years after that should be impossible. They should have left ten billion years ago. That is seriously late for work. They are stragglers.
The mystery was solved when it was realized that they are new main sequence stars produced by mergers.
