The University of London Observatory – UCL’s astronomical observatory in Mill Hill, North London – has to deal with England’s murky skies and London’s bright lights, but it can still make some impressive images. Messier 51, seen in the picture above, is actually not one galaxy but two – a large spiral galaxy (Messier 51a) interacting with a smaller dwarf galaxy (NGC 5195). Over the next few hundred million years, they will merge together into one larger galaxy.
Such mergers are quite common. Large spiral galaxies can absorb dwarf galaxies without major disruption to their shapes, though the (rarer) mergers between similarly-sized galaxies tend to destroy all structure, leaving a largely featureless elliptical galaxy. This will be the fate of the Milky Way when it merges with the Andromeda Galaxy in a few billion years time.
The Messier 51 pair are a popular target for amateur astronomers – on a dark night, even relatively basic telescopes can pick out the very faint comma-shape of the galaxy pair, visible near one end of the Plough (Ursa Major).
The picture is one of several newly processed images just published by UCL’s observatory, based on data gathered by astronomy students. The observatory now routinely archives all the digital data gathered with its Celestron telescopes, which are used intensively for undergraduate teaching. This growing archive of data means that multiple observations can be easily combined into a single image, improving contrast and revealing faint details that would otherwise be invisible.
A selection of several dozen of these images from the observatory, with multiple observations processed and combined to form colour composites, is available online to the public. They are free to reuse and reproduce.