The presence of two previously undiscovered galaxies about 29 billion light-years away suggests that our understanding of the early universe is disturbingly deficient.
We introduce REBELS-12-2 and REBELS-29-2 – two galaxies that we until very recently did not even know existed. The light from these galaxies took 13 billion years to get here when these objects were formed shortly after the Big Bang. The ongoing expansion of the universe places these ancient galaxies about 29 billion light-years from Earth.
New research published in Nature suggests that REBELS-12-2 and REBELS-29-2 had escaped being discovered until this time because our view of these galaxies is clouded by thick layers of cosmic dust. The Hubble Space Telescope, however powerful it may be, could not look 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 random accident.
“We were looking at a sample of very distant galaxies that we already knew existed from the Hubble Space Telescope. And then we noticed that two of them had a neighbor that we did not expect to be there at all,” Pascal Oesch explains. astronomer from the Cosmic Dawn Center at the Niels Bohr Institute in Copenhagen, in a statement. “Since both of these neighboring galaxies are surrounded by dust, some of their light is blocked, making them invisible to Hubble.”
Oesch is an expert in finding some of the most distant galaxies in the universe. Back in 2016, he and his colleagues discovered the 13.4 billion-year-old GN-z11 galaxy, setting a cosmic distance record. GN-z11 was formed only 400 million years after the Big Bang.
The new paper describes how ALMA and the new observation technique, developed by Oesch and his colleagues, may be able to spot similarly hidden ancient galaxies. And there are apparently many more waiting to be discovered. Astronomers compared the two newly discovered 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 sky,” Oesch said.
To which he added: “Before we can begin to understand when and how galaxies were formed in the universe, we first need a proper inventory.” In fact, the new paper claims that more ancient galaxies existed in the early universe than previously thought. This is important because the earliest galaxies formed the building blocks of subsequent galaxies. So until we have a “correct account,” as Oesch put it, astronomers could work with a flawed or otherwise inaccurate model of the early universe.
The task now will be to find these missing galaxies, and fortunately a future instrument promises to make this work significantly easier: the Webb Space Telescope. This next-generation observatory, Oesch said, “will be much more sensitive than Hubble and able to study longer wavelengths, which should allow us to see these hidden galaxies with ease.”
The new paper is thus testable, as observations made by Webb are likely to confirm, disprove or further refine the researchers’ predictions. The space telescope is scheduled to be launched from French Guiana on Wednesday, December 22 at 7:20 ET (4:30 PT).
More: The Webb telescope is not damaged after mounting incident, says NASA.