This is Palomar 2, one of 15 globular star clusters originally discovered by Hubble—not the space telescope, but its legendary namesake, as Edwin Hubble was part of the project that first discovered these clusters back in the 1950s.
This cluster was identified during the Palomar Observatory Sky Survey, hence the name Palomar 2. Its discovery is unusual mostly because it happened so late; most clusters were discovered long before the 1950s. After all, star clusters are giant collections of thousands or, in the case of globular clusters, millions of the brightest objects in the sky. As such, it took an unusual combination of factors for a globular cluster like Palomar 2 to evade detection even after centuries of telescopic observation.
According to NASA, Palomar 2 and the other 14 hidden clusters discovered by Hubble and his colleagues must either be very far away, situated behind thick clouds of dust, or have lost most of their stars, resulting in their current dim appearance. This image — which, yes, was taken by Hubble the telescope, rather than Hubble the astronomer — is the best view yet of the cluster. Here's some more info from the NASA and ESA scientists behind the find:
This particular cluster is unique in more than one way. For one, it is the only globular cluster that we see in this part of the sky, the northern constellation of Auriga (The Charioteer). Globular clusters orbit the center of a galaxy like the Milky Way in the same way that satellites circle around the Earth. This means that they normally lie closer in to the galactic center than we do, and so we almost always see them in the same region of the sky. Palomar 2 is an exception to this, as it is around five times further away from the center of the Milky Way than other clusters. It also lies in the opposite direction — further out than Earth — and so it is classed as an "outer halo" globular. It is also unusual due to its apparent dimness. The cluster is veiled by a mask of dust, dampening the apparent brightness of the stars within it and making it appear as a very faint burst of stars.
For more, check out NASA's website.
Image credit: ESA/NASA, Hubble.