The presence of two previously undetected galaxies some 29 billion light years away suggests our understanding of the early universe is upsettingly deficient.
Introducing REBELS-12-2 and REBELS-29-2—two galaxies that, until very recently, we didn’t even know existed. The light from these galaxies took 13 billion years to get here, as these objects formed shortly after the Big Bang. The ongoing expansion of the universe places these ancient galaxies at roughly 29 billion light years from Earth.
New research published in Nature suggests REBELS-12-2 and REBELS-29-2 had escaped detection up until this point because our view of these galaxies is clouded by thick layers of cosmic dust. The Hubble Space Telescope, as mighty as it is, could not peer through the celestial haze. It took the ultra-sensitive ALMA radio telescope in Chile to spot the galaxies, in what turned out to be a fortuitous accident.
“We were looking at a sample of very distant galaxies, which we already knew existed from the Hubble Space Telescope. And then we noticed that two of them had a neighbor that we didn’t expect to be there at all,” Pascal Oesch, an astronomer from the Cosmic Dawn Center at the Niels Bohr Institute in Copenhagen, explained in a statement. “As both of these neighboring galaxies are surrounded by dust, some of their light is blocked, making them invisible to Hubble.”
Oesch is an expert at finding some of universe’s farthest galaxies. Back in 2016, he and his colleagues detected the 13.4 billion-year-old GN-z11 galaxy, setting a cosmic distance record. GN-z11 formed a mere 400 million years after the Big Bang.
The new paper describes how ALMA and the new observing technique developed by Oesch and his colleagues might be able to spot similarly obscured ancient galaxies. And there’s apparently many more awaiting discovery. The astronomers compared the two newly detected galaxies to previously known galactic sources in the early universe, leading them to suspect that “up to one in five of the earliest galaxies may have been missing from our map of the heavens,” Oesch said.
To which he added: “Before we can start to understand when and how galaxies formed in the Universe, we first need a proper accounting.” Indeed, the new paper asserts that more ancient galaxies existed in the early universe than previously believed. This is significant because the earliest galaxies formed the building blocks of subsequent galaxies. So until we have a “proper accounting,” as Oesch put it, astronomers could be working with a deficient or otherwise inaccurate model of the early universe.
The task now will be to find these missing galaxies, and thankfully an upcoming instrument promises to make this job considerably easier: the Webb Space Telescope. This next-gen observatory, said Oesch, “will be much more sensitive than Hubble and able to investigate longer wavelengths, which ought to allow us to see these hidden galaxies with ease.”
The new paper is thus testable, as observations made by Webb are likely to confirm, negate, or further refine the predictions made by the researchers. The space telescope is scheduled to launch from French Guiana on Wednesday December 22 7:20 a.m. ET (4:30 a.m. PT).