#intergalactic medium

Space chicken joke from Dear Hank & John episode 325.

Caltech astronomers have taken unprecedented images of the intergalactic medium (IGM)—the diffuse gas that connects galaxies throughout the universe—with the Cosmic Web Imager, an instrument designed and built at Caltech. Until now, the structure of the IGM has mostly been a matter for theoretical speculation. However, with observations from the Cosmic Web Imager, astronomers are obtaining our first 3-D pictures of the IGM.  

THE INTERGALACTIC MEDIUM UNVEILED: Cosmic Web Imager directly observes Dim Matter PhysOrg News

A few words about INTERGALACTIC SPACE 

THE VOIDS [Wikipedia] The vast empty spaces between filaments (the largest-scale structures in the Universe), which contain very few, or no, galaxies are called the voids  

IGM — THE INTERGALACTIC MEDIUM [Wikipedia] Surrounding and stretching between galaxies, there is a diffuse gas that is organized in a galactic filamentary structure. This material is called the intergalactic medium.

The density of the IGM is 5-200 times the average density of the Universe.

It consists mostly of ionized hydrogen; i.e. a plasma consisting of equal numbers of electrons and protons.

As gas falls into the intergalactic medium from the voids, it heats up to temperatures of 105 K to 107 K and is called the warm–hot intergalactic medium (WHIM). (Although the gas is very hot by terrestrial standards, 105 K is often called "warm" in astrophysics.)

Computer simulations and observations indicate that up to half of the atomic matter in the Universe might exist in this warm-hot, rarefied state.

Until now, the structure of the IGM has mostly been a matter for theoretical speculation. However, with observations from the Cosmic Web Imager, an instrument designed and built at Caltech and deployed on the Hale 200-inch telescope at Palomar Observatory, astronomers are obtaining our first three-dimensional pictures of the IGM.

The Cosmic Web Imager has already detected one possible spiral-galaxy-in-the-making that is three times the size of our Milky Way.

Read more ...

In its earliest years, the universe was so hot that electrons and protons could not bind together in neutral atoms: all of the gas in the cosmos was ionized. Then, after 380,000 years of expansion, the universe cooled enough for hydrogen atoms and some helium (about 25%) to form. Much later in cosmic history -- the precise dating is an active area of current research but perhaps after a few hundred million years -- the first generation of stars emerged from the vast expanses of atomic gas, and these stars emitted enough strong ultraviolet light to re-ionize the neutral hydrogen in their vicinity. As the universe continued to expand and evolve, newer generations of stars continued to re-ionize the hydrogen until at some time most gas between galaxies (the intergalactic medium) was ionized once again. The epoch of re-ionization is an important diagnostic tool because it traces when the first generations of stars were being made, and it provides crucial details about the early evolution of the universe.