This beautiful picture is of a distant collection of galaxies called the Abell S0740 galaxy cluster, captured by the Hubble Space Telescope. It’s located more than 450 million light years away in the constellation Centaurus.
That great big blob in the centre is the giant ellipital galaxy ESO 325-G004, and contains as much as 100 billion stars. The galaxy is surrounded by hundreds of thousands of globular star clusters, each of which contains hundreds of thousands of stars. The galaxy is then surrounded by hundreds of other elliptical and spiral galaxies.
Bad Astronomer Phil Plait has a really great write up on the photograph to help you understand it better.
Original Source: Hubble News Release