Intergalactic space refers to the vast, largely empty regions between galaxies. It represents the largest volume of space in the universe, contrasting sharply with the dense, star-filled environments within galaxies where matter is concentrated. Understanding intergalactic space provides insights into the universe’s large-scale structure and evolution.
The Extreme Emptiness
Intergalactic space is characterized by an extreme vacuum, far sparser than any vacuum achievable on Earth. While a laboratory vacuum might contain billions of atoms per cubic meter, intergalactic space holds only about one hydrogen atom per cubic meter. This density is significantly lower than the space between stars within a galaxy, which can contain a million particles per cubic meter. Matter is spread incredibly thinly across these cosmic distances.
Consider a galaxy the size of a grain of sand. The intergalactic space between galaxies would then be comparable to the vast distances between individual grains of sand scattered across an entire beach. This illustrates that while not absolutely devoid of matter, intergalactic space is very close to a perfect vacuum. The lack of particles means encounters between them are exceedingly rare, making these regions remarkably transparent and cold.
Components of Intergalactic Space
Despite its extreme emptiness, intergalactic space contains diffuse matter and energy. The most prevalent component is the Intergalactic Medium (IGM), a rarefied plasma primarily consisting of ionized hydrogen and helium, with trace amounts of heavier elements. This gas is so spread out that it contributes minimally to the overall density of the universe, yet accounts for a significant portion of the ordinary matter in the cosmos. The IGM can reach temperatures ranging from thousands to millions of degrees Kelvin.
Intergalactic space is also traversed by cosmic rays, which are high-energy particles like protons, electrons, and atomic nuclei traveling at nearly the speed of light. These particles originate from energetic astrophysical phenomena, including supernovae and active galactic nuclei. The Cosmic Microwave Background (CMB) radiation is another pervasive component, a faint glow of microwaves filling all space. The CMB is a cooled remnant of the universe’s earliest moments after the Big Bang, providing a uniform background radiation field throughout intergalactic regions.
Intergalactic Space and Cosmic Evolution
Intergalactic space plays a substantial role in the universe’s large-scale structure and evolution. The IGM forms a vast, interconnected network known as the cosmic web. This web consists of immense gas filaments that link galaxies and galaxy clusters, interspersed with nearly empty voids. These filaments act as conduits, channeling gas and matter, including baryonic matter, towards denser regions where galaxies reside.
This continuous flow of material from the IGM influences how galaxies form and grow, acting as a reservoir for star formation. Simulations suggest that over 60% of the hydrogen formed during the Big Bang resides within these intergalactic filaments. Intergalactic space is also where the majority of the universe’s mysterious dark matter and dark energy are thought to reside. These components, which do not interact with light, exert gravitational influences that dictate the expansion and overall structure of the universe on these vast scales.