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Astronomers Capture First Image of 'Cosmic Web' That Holds Galaxies Together

quasar UM 287 (credit S. Cantalupo)

Just a few years ago, indirect evidence, or “signatures”, of gigantic cosmic “tendrils”, or filaments, was discovered lurking around distant multi-galactic formations.

Vast in scale but invisible, such filamentous structures apparently account for much of the missing matter required to keep galaxies intact (and prevent them from dispersing randomly throughout the cosmos). These intricately branching filaments — believed to be composed of some combination of gas and dark matter — have been described as constituting a sort of cosmic back bone or “web” that connects (and contains) all  galaxies and supra- galactic formations (“galaxy clusters”) in our universe. However, until recently, astronomers have not been able to directly image this structure (note: a team from the University of Munich Observatory had previously observed one such filament due to its perpendicular orientation to the Earth; see link below).

But now a team of astronomers from the University of California at Santa Cruz have successfully imaged a segment of this cosmic web thanks to fortuitous convergence of a quasar and a giant cloud of gas — aided by the high-res imaging capability of the Keck Space Telescope. Results of the successful imaging were reported in the  Jan. 19 edition of the journal Nature.

Normally, such filaments are invisible to the eye (even aided by powerful telescopes) because they possess low density and do not reflect or radiate light as other galactic objects do. What is needed is some sort of cosmic “flashlight” (or perhaps “black light”) that could by chance reveal what is hidden in the darkness of intergalactic space.

Such a source of illumination was found in the form of an extremely bright mass known as a quasar (which sands for quasi stellar radio source) that happened to be surrounded by a vast cloud of stellar gas (of a different sort than that composing a filament).

The quasar, called UM287 (see top image, center of photo), is located a mere 10 billion light years distant, and is embedded in a bluish nebula (a giant cloud of stellar gas) extending some 2 million light years across. the quasar is so bright that it’s light causes the surrounding hydrogen gas to glow. This in turn resulted in a dramatic boosting of what’s known as Lyman alpha radiation — radiation that the Hydrogen gas normally emits, but at lower levelsso much so that a large area of the surrounding region of space became detectable.

And within this now irradiated space was found a nexus of cosmic filaments — the first direct (imaged) evidence of the cosmic web that connects all galactic structures in the universe. Filaments constituting this web frequently intersect each other, and where they do, clusters of galaxies tend to form.

But before any actual imaging of the filaments could happen, the team of astronomers had to first calculate the wavelength of the Lyman radiation emanating from the nebula. Once they were able to do this, they could then “tune” the Keck telescope (located in Hawaii) to that same wavelength, and thus capture an image of this once hidden region of space.

The imaging experiment revealed a vast cloud of gas stretching some 2 million light years across the intergalactic void (so far, the largest such expanse ever found). But this cloud contained intriguing features: areas of dense gas broken up by areas of darker (“emptier”) space. The areas containing the densest concentrations of gas are the filaments with the dark patches being the gaps between filaments — what we see as the gaps and “empty” spaces between galaxies in a galactic cluster.

cosmic web (image by Anatoly Klypin and Joel Primack, S. Cantalupo)Image Description: A computer (“large scale dark matter”) simulation showing how matter in the universe is distributed in a “cosmic web” of filaments. The inset is a zoomed-in, high-resolution image of a smaller part of the cosmic web, 10 million light-years across, from a simulation that includes gas as well as dark matter (credit: Anatoly Klypin and Joel Primack, S. Cantalupo; source: see link, below)

In a press statement, team member Sebastiano Cantalupo of UC Santa Cruz commented:

“This is a very exceptional object…It’s huge, at least twice as large as any nebula detected before, and it extends well beyond the galactic environment of the quasar.”

Since the quasar’s “halo effect” is limited in its range, astronomers believe that they are seeing only a smaller segment of a vastly more extended cosmic structure.

In another press statement, co-author and Professor of Astronomy and Astrophysics at UC Santa Cruz J. Xavier Prochaska, commented on the research:

“[It] provides a terrific insight into the overall structure of our universe…[since the] quasar is illuminating diffuse gas on scales well beyond any we’ve seen before, giving us the first picture of extended gas between galaxies.”

For more background reading on cosmic filaments (or “tendrils”), check out my previous post on PS: Dark Matter ‘Tendrils’ Observed for First Time C Revealing the Hidden Structure of the Universe

Top image: [quasar UM287] credit: S. Cantalupo

Some source material for this post (including photos and quotes) came from the Business Insider article ‘Astronomers Capture The First Image Of The Mysterious Web That Connects All Galaxies In The Universe‘ by Dina Spector.




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