Here on Earth, humans are but a speck in the vastness of the cosmic web—a tangled tapestry of matter that connects far-flung galaxies with thin, tenuous threads of gas.
But even from the less-than-ideal vantage point in this teeny pocket of the cosmos, astronomers have managed to generate the first detailed picture of the massive structure that ties the known universe together. It’s our best view of the cosmic web yet, the researchers report today in the journal Science, and shows its connective tissue stretches millions of light-years long.
Unraveling the architecture of the cosmic web—which is believed to have formed in the wake of the big bang 13.8 billion years ago—is crucial for understanding the universe’s origins and evolution. But before now, most evidence of the cosmic web’s existence has been indirect. Unlike the bright, matter-dense galaxies they tie together, the web’s gaseous threads are thin and sparse and emit only faint signatures of light.
Every once in a while, however, threads can be backlit by a galaxy bursting with light generated by newborn stars or the matter-guzzling activity of black holes. In theory, these stellar spotlights could infuse the web’s gassy filaments with enough extra energy to make them visible from Earth.
That’s what a team led by astrophysicist Hideki Umehata of the RIKEN Cluster for Pioneering Research and the University of Tokyo has managed to detect some twelve billion light-years from Earth. Using the Multi Unit Spectroscopic Explorer (MUSE) on the European Southern Observatory’s Very Large Telescope in Chile, the researchers zeroed in on an assembling cluster of galaxies called SSA22.
The brightest emission in their image was the cluster itself. But also present were two subtly illuminated cosmic web filaments, each about 3 million light-years across, and studded with a series of bright white galaxies.
“This is the first time we really see the filaments connecting a number of galaxies,” Umehata told Jonathan O’Callaghan at New Scientist.
And the threads aren’t static. The gas within is probably on the move, trickling up and down these intergalactic bridges to fuel stellar activity in the galaxies they connect, Umehata told Hannah Devlin at The Guardian. If that’s correct, it supports the idea that galaxies are seeded at the intersections of filaments, where matter concentrates—something that could have governed the formation of the universe in its earliest days.
“This is really just the tip of the iceberg for the cosmic web,” Erika Hamden, an astrophysicist at the University of Arizona who wrote an accompanying perspective piece on the study, but was not involved in the research, told O’Callaghan. “It’s a confirmation that it should all be there. It’s pretty wild. You look at space and you think it’s empty, but it’s not actually. There’s this gigantic, wonderful structure.”