Hubble image of spiral galaxy PGC 54493, located in the constellation of Serpens (The Serpent). It is part of a galaxy cluster that has been studied by astronomers exploring weak gravitational lensing, a phenomenon caused by the uneven distribution of matter (including dark matter) throughout the Universe. Dark matter is one of the great mysteries in cosmology. It behaves very differently from ordinary matter as it does not emit or absorb light or other forms of electromagnetic energy. PGC 55493 has also been studied in connection with an effect known as cosmic shearing. This is a weak gravitational lensing effect that creates tiny distortions in images of distant galaxies.