Mysterious 'Dim Matter' Revealed with Unprecedented Images of Intergalactic Medium

With some new, unprecedented images, astronomers are learning a bit more about the intergalactic medium, the diffuse gas that connects galaxies throughout the universe. Using the Cosmic Web Imager, the researchers have managed to capture the first three-dimensional pictures of the intergalactic medium (IGM).

Until now, the structure of the IGM has mostly been a matter of speculation. Since the late 1980s and the early 1990s, researchers have predicted that primordial gas from the Big Bang is not spread uniformly throughout space; instead, it's distributed in channels that span galaxies and flow between them, creating a type of "cosmic web." Now, though, it seems that scientists may have some hard evidence for the shape of this web.

"I've been thinking about the intergalactic medium since I was a graduate student," said Christopher Martin, the scientist who conceived the Cosmic Web Imager, in a news release. "Not only does it comprise most of the normal matter in the universe, it is also the medium in which galaxies form and grow."

Martin describes the diffuse gas of the IGM as "dim matter." This distinguishes it from the bright matter of stars and galaxies and the dark matter and energy that compose most of the universe. Before the Cosmic Web Imager, this dim matter was observed primarily through the foreground absorption of light, indicating the presence of matter, occurring between Earth and a distant object.

In this case, the researchers spotted cosmic filaments in the vicinity of two very bright objects, a quasar called QSO 1549+19 and a so-called Lyman alpha blog in an emerging galaxy cluster known as SSA22. The cosmic filament was about one million light-years long and flowed into the quasar. In addition, three other filaments surrounded the Lyman alpha blob.

The findings are huge for better understanding dim matter. Now, researchers have turned their sights on observing the IGM with other tools. Plans are underway for observations of the IGM from a telescope aboard a high-altitude balloon. The findings should tell scientists a little bit more about the universe that we live in.

The findings are published in The Astrophysical Journal in two different papers here and here.