The space between galaxies stretches millions of light-years. This space may seem like an empty void but there’s a lot more happening than you’d think. There is actually between 50%-80% of all ordinary matter found here. Read on to learn more about what this matter is and where it came from.

Intergalactic medium

The matter between galaxies is known as the intergalactic medium or IGM. This matter is made up of ionized hydrogen. This hot matter contains hydrogen that has lost electrons. It has bits of heavier elements such as oxygen, carbon, and silicon. The elements can only be seen by the light they show when they pass by. One of the first active galaxies, quasars, was discovered in the 1960s. This bright, active galaxy, was discovered to have missing pieces. They had been absorbed by something between the scientists’ telescopes and the quasar. What was being seen is the gas of the intergalactic medium. Scientists discovered filaments of gas, heavy elements and a vast web containing more matter than all of the other galaxies combined. Much of this gas is likely gas that has been leftover from the Big Bang. The heavier elements are thought to be old stardust that has been spewed from the galaxies. The most remote areas of the intergalactic medium are isolated from the neighboring galaxies. Although they are further away, these actually influence the other galaxy’s gravitational pull. The galaxy accumulates slowly at a rate of one solar mass per year. This is equal to the mass of the sun and the rate of a star formation in the Milky Way. The intergalactic medium is the gas that forms stars in the galaxies. If we didn’t have this gas falling in, star formation would stop as the gas in the galaxy gets used.

How the intergalactic medium is studied

To probe the intergalactic medium, astronomers have begun looking at fast radio bursts that are coming from distant galaxies. Using this technique and examining quasar light, scientists are able to study the intergalactic medium to see the different temperatures and densities. If you measure the temperatures of the gas, you can find out where it came from. This shows how it is heated as well as how it appeared there. Gas isn’t the only thing between galaxies. Stars have also been found in this space. These stars are known as intergalactic stars. They are rouge stars that scientists believe have been thrown from their original galaxies by collisions with other galaxies or black holes. It’s very common for stars to roam around the void. The Astrophysical Journal showed there are over 650 stars at the edge of the Milky Way and there could be even trillions more. They also showed that half of the light shown from stars is actually sourced by stars out of the galaxy.

Extragalactic background light

In recent studies, astronomers investigated the extragalactic background light. This is the amount of light emitted by all of the stars in the universe over the history of time. Before, research had shown that the fluctuations in the light didn’t appear to come from a known galaxy. The research suggested that the fluctuations of light may be coming from primordial galaxies. These are the earliest galaxies whose light hasn’t even been detected yet. To look further into these fluctuations, scientists and researchers have developed the Cosmic Infrared Background Experiment. The Cosmic Infrared Background Experiment is also known as CIBER. CIBER is made of a set of telescope designed specifically to study and analyze the properties of the extragalactic background light. The Cosmic Infrared Background Experiment uses small sounding rockets to research missions that don’t orbit but they go into space. This was a quick and affordable way to conduct these experiments. The research showed fluctuations in the extragalactic background light in the near-infrared region. We know this because as the universe expanded, the ultraviolet and visible light from the stars should have reddened over time. The results were confirmed by using NASA’s Spitzer Space Telescope. The results showed that the primordial galaxies weren’t actually the source of background light fluctuations.

Scientists confirmed that the background light fluctuations were too bright of blue to come from primordial galaxies. The first galaxies were very old and the light that could be seen now would have been emitted billions of years ago. By now, since this light has traveled over such a long period of time, it should appear very dim. It would also be very red because gas had to pass through it. The finding of the bright, blue light means that the fluctuations likely come from intrahalo light. Intrahalo light is created by stars that are thrown into space during collisions and mergers of the galaxies. Research shows that there is just as much light coming from intergalactic stars as there is from stars that are located within the galaxies.

Newfound stars

The newfound stars show that there is a high amount of ultraviolet light that is missing from the universe. This is known as the missing baryon problem. Baryons are subatomic particles that include the neutrons and protons that makeup atoms inside of normal matter. The formation and evolution of the universe show that there are a lot more baryons than can currently be seen by scientists. What baryons the astronomers can see in the local cosmic areas are only half of what they predict actually exists. Scientists are also analyzing data from instruments on sounding rockets that have recently launched. This will show scientists more about how stray stars are made.