By illuminating dark matter with quasar light from around a super-massive black hole, astronomers have seen for the first time ever the strands that constitute a cosmic web and hold the universe together. Scientists in the US and Germany have been able to confirm what has long been suspected, but only before “observed” via computer simulations. Filaments or threads of dark matter have long been presumed to link together the phenomenal voids across intergalactic space. As these don’t emit light though, they have not been possible to see.
Using a quasar as a surrogate flashlight, they were able to make visible a stream of hydrogen gas said to be two million light years in length. Such filaments have been searched for since the 1990’s when the European Space observatory described them as the “skeleton of the universe.” Now, as explained in today’s edition of Nature, the evidence has been seen by human eyes. Cosmological theory, that the cosmos is spun together by strands of diffuse gas millions of light years across comes closer to being understood. The predictions seem to be accurate, although the models are already been questioned as having underestimated. The amount of gas in this nebula is at least ten times more than simulations have suggested. These new observations both confirm and yet challenge all previous assumptions about the universe and its composition.
The research team used the Very Large Telescope located in Chile with a special filter fitted to it. They then honed in on quasar UM 287 to borrow its extraordinarily bright light to enhance visibility of the stream of gases. UM 287 is 10 billion light years from earth and emits intense radiation. Using a quasar in this way, they wrote in the journal, has the ability to show us the “densest knots” in the “cosmic web.” Just like spiders in their webs, the galaxies seem to inhabit the complex intersections where most of the strands join in a cluster.
Spokesman, and postdoctoral fellow at UC Santa Cruz, Sebastiano Cantalupo, said that they were lucky that the flashlight-like beam from the quasar so happened to point toward a nebula and caused the gas to glow. This allowed them to see part of the filament. He described it as an exceptional object, and that it extended well beyond the “galactic environment” of UM 287.
Co-author of the report, J.Xavier Prochaska, confirms they have seen the “first picture of extended gas between galaxies.” The glow from the hydrogen gas was caused by ultraviolet light from the quasar – Lyman alpha radiation. This emitted light was then stretched by the universe’s expansion so that by the time it reached the telescope it was a highly visible color violet. The image was then obtained by knowing the distance to the quasar and being able to build a filter specifically for the wavelength of the Lyman alpha radiation at that distance.
This is the biggest breakthrough since 2012 when a team based in Hawaii found a “bridge” of dark matter between two galaxy clusters named Abell 222 and 223. In that instance however, it was inferred not through direct observation but through calculating distortions in light that passed between them, from other, more distant, galaxies.
The secrets of the development and structure of our own galaxy, the Milky Way, and all others, long thought to be held in a cosmic web, now come closer to being understood. The skeletal links of strings of gases are no longer just inferred, one has been illuminated, and this is turn, illuminates further study.
By Kate Henderson