M13 is a dense, spherical cluster of old stars, orbiting the Milky Way’s centre in the galactic halo. Some globular clusters like M13 undergo what’s known as core collapse, which is when gravity pulls the stars into a very compact centre. Around 20% of globulars in the Milky Way are core collapsed, but this isn’t the case yet with M13, as its stars are dense but fairly evenly spread out.

In the close-up below we can see quite a few “blue straggler” stars. These stars are younger, and have hotter surface temperatures, than most of the cluster’s stars. They probably formed in one of two ways:

1. Two old, low-mass stars merging, leading to more mass, so higher core pressure, and resulting in a hotter and more luminous “rejuvenated” star.
2. A binary star system, where one star collects mass from another. The star that gains mass can then undergo the steps outlined above, leading to it becoming somewhat refreshed.

There are several galaxies in the background of my image, with the most prominent of these being NGC 6207 and IC 4617.

NGC 6207 looks to be the larger of the two, but that’s just because it’s closer, lying 30 million light-years from Earth; a mere stone’s throw compared to IC 4617’s colossal 550 million light-years! NGC 6207 has a diameter of 34,000 light-years, while IC 4617 is about 115,000 light-years across, putting it in the same ballpark as our own Milky Way, size-wise.