Interstellar matter refers to the gas and dust found in the space between stars in a galaxy. This material primarily consists of hydrogen and helium, along with trace amounts of heavier elements. It plays a crucial role in the formation of new stars and planetary systems, as it can collapse under gravity to create dense regions. The dust in interstellar matter can absorb and scatter light, affecting our observations of distant celestial objects. Additionally, interstellar matter can also contain complex organic molecules, which are of interest in the study of the origins of life and the potential for extraterrestrial life.