Space and Physics

Secrets Of "Dim Matter" Revealed

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Justine Alford

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clockApr 30 2014, 10:20 UTC
801 Secrets Of "Dim Matter" Revealed
Christopher Martin and Robert Hurt. Left: the Lyman alpha blob observations taken from the Cosmic Web Imager. Right: simulation of the cosmic web.

Throughout the universe, galaxies are connected by a diffuse gas called the intergalactic medium (IGM). The structure of this gas was previously unknown, but for the last few decades scientists theorized that it was not uniformly distributed throughout space and was instead more like a web of interconnecting and crisscrossing filaments. Thanks to new observations from the Cosmic Web Imager, astronomers have now managed to obtain their first 3D images of the IGM, and they already believe that they might have stumbled upon a new spiral galaxy amid formation.


Scientists approximate that the universe is composed of 96% dark energy and dark matter; the other 4% is normal matter. Of this remaining 4% a mere 1% is the bright matter of stars, planets and galaxies, and the IGM “dim matter” makes up the rest.

According to Caltech professor of physics Christopher Martin, before the Cosmic Web Imager was invented there was no way to tell how the IGM was dispersed across three dimensions. Instead astronomers relied on the foreground absorption of light that occurred between Earth and distant objects, but an incomplete picture was given. The Cosmic Web Imager, built by Caltech, takes simultaneous pictures at multiple wavelengths which divulge information on the composition, mass and velocity of objects in space.

In order to gain a more detailed understanding of the IGM structure, scientists used this instrument to look at the surrounding areas of two very bright objects; a quasar (nucleus of a young galaxy) called QSO 1549+19, and something called a Lyman alpha blob which lies within the emerging galaxy cluster SSA22. They found a single filament feeding into the quasar which was one million light-years long, and three filaments flowing into the Lyman alpha blob which seem to be altering its dynamics. Lyman alpha is a specific UV wavelength emitted by hydrogen, which is predicted to make up the majority of these filaments.

These filaments are estimated to have origins approximately 2 billion years after the Big Bang. “In the case of the Lyman alpha blob, I think we’re looking at a giant protogalactic disk,” said Martin in a news release. “It’s almost 300,000 light-years in diameter, three times the size of the Milky Way.”


The team are now looking at building an improved version of the Cosmic Web Imager that is able to detect IGM filaments without relying on unusually bright objects such as the two used so far. 

Space and Physics
  • Intergalactic medium,

  • Cosmic Web Imager,

  • Caltech