The gap between galaxies, such as the one between the Milky Way and the Andromeda Galaxy, is not a complete void. While the intergalactic space is significantly less dense than the regions within galaxies, it is not completely empty. Here are some of the key features that exist in the gap between galaxies:
Intergalactic Medium (IGM): The intergalactic medium is a diffuse mixture of gas and plasma that fills the vast regions between galaxies. It primarily consists of hydrogen and helium, along with trace amounts of other elements. Although the density of the intergalactic medium is extremely low compared to the interstellar medium within galaxies, it is not entirely devoid of matter.
Dark Matter: The presence of dark matter is thought to be ubiquitous throughout the universe, including the gaps between galaxies. Dark matter is a hypothetical form of matter that does not interact with light and cannot be directly observed. Its presence is inferred through its gravitational effects on visible matter, such as stars and galaxies.
Filaments and Cosmic Web: On larger scales, the distribution of matter in the universe forms a complex cosmic web-like structure. The cosmic web consists of vast filaments composed of dark matter and gas, which connect galaxies and galaxy clusters. These filaments can extend across enormous distances, even spanning the gaps between galaxies.
Dwarf Galaxies: In addition to the large spiral and elliptical galaxies like the Milky Way and Andromeda, there are smaller galaxies known as dwarf galaxies. Dwarf galaxies are less massive and have fewer stars compared to their larger counterparts. They can exist in the outskirts of galaxy clusters and the gaps between larger galaxies.
Extragalactic Background Light: The extragalactic background light (EBL) is the cumulative radiation from all sources outside our Milky Way galaxy. It consists of various wavelengths of light emitted by stars, galaxies, and other astrophysical objects. The EBL permeates the intergalactic space and contributes to the overall background glow.
It's important to note that while these features exist in the gap between galaxies, their density and distribution can vary considerably. The gaps between galaxies still have significantly lower matter densities compared to the regions within galaxies, but they are not completely devoid of matter and exhibit a range of cosmic structures and phenomena.