M-4 again

Since all those star cluster pictures tend to look alike, I thought I'd check the Hubble Telescope website and see if there were some prettier ones to look at. I found a neat one of M-4 that I had seen before but forgotten about. It's a close up of one section of the cluster, and if you look close you'll see a green circle a little more than halfway up on the right edge of the picture. The first thing I thought when I first saw this picture several years ago was Wow, that green circle thingy doesn't even look natural. No, it's not a natural green circle in the middle of space. (Insert mental image of me blushing.) In reality, that circle was put there by a computer to mark a particular star on the picture. The star is a pulsar (I'll explain that some other time) and the reason they marked it was because it's orbited by the oldest planet known.

This is an even tighter close up of the same picture, just so you can see there's something in the circle.