Free Astronomy Magazine May-June 2021

MAY-JUNE 2021 tical galaxies lurking in the back- ground. The long exposure time of this deep observation — arguably the deepest image of NGC 1003 ever captured — allowed these usually overlooked background cluster gal- axies to be captured in breathtaking detail. Deep images such as this one have had an important role in shaping our understanding of the Universe. In 1995, the Hubble Space Telescope famously observed a tiny, nonde- script patch of sky for 10 days to cre- ate the Hubble Deep Field. The ob- servations revealed thousands of distinct galaxies, showing that our Universe is a surprisingly crowded place. While the Hubble team deliberately avoided bright galaxies for their ob- servation, this ground-based obser- vation is littered with galaxies of all shapes and sizes — a spectacular backdrop for this portrait of NGC 1003. As well as revealing the host of background galaxies, the long exposure time of this observation allowed the researchers to capture the faint outer reaches of NGC 1003, which are threaded through with bright tendrils of stars. Equally eye- catching is the bright heart of the galaxy, which is surrounded by clouds of dense dust. NGC 1003 resides in front of a galaxy cluster — a vast collection of galax- ies bound together by gravity. These structures are among the most mas- sive in the known Universe, and out- weigh the Sun by a factor of a thou- sand trillion. Just as stars can be grouped into clusters, and these star clusters into galaxies, galaxies themselves form clusters and even superclusters — building up the large-scale structure of our Universe. !