What has Hubble learned from star clusters?

The NASA/ESA Hubble Space Telescope has observed many star clusters. As well as being scientifically interesting, these clusters produce stunning images, appearing like sparkling baubles in the sky. This episode of the Hubblecast looks at how Hubble has studied and imaged these beautiful objects, also introducing a striking new image of Messier 15, one of the oldest globular clusters in our skies. This is the best ever image of this cluster, which contains over 100 000 stars, a planetary nebula known as Pease 1 (otherwise named PN Ku 648 or Kürster 648), and something more exotic: at its core, it is thought to host a rare type of black hole.