Final answer:
Dark matter is an unseen component that exists throughout the universe, and observations across different types of galaxies suggest that dark matter is present in every type of galaxy, affecting their gravitational dynamics.
Step-by-step explanation:
Dark matter is a non-luminous component of the universe that does not emit, absorb, or reflect light, making it very difficult to detect directly. Evidence for dark matter comes from its gravitational effects on visible matter, radiation, and the large-scale structure of the universe. Based on astronomical observations, dark matter is present in and around all types of galaxies, including spiral, elliptical, and irregular galaxies. For example, studies of the rotation speeds of outer galactic regions in spiral galaxies like the Milky Way and Andromeda, as well as the dynamics of stars in elliptical galaxies, indicate the presence of dark matter in those galaxies. Furthermore, dark matter affects the orbits of galaxies in clusters, pointing to its ubiquitous presence. Therefore, dark matter is found not just in a specific type of galaxy but in every type of galaxy.