Spotting the universe’s earliest structures is a challenge for astronomers. Evidence of these massive galaxies is hard to find, but they do leave behind some tracks if researchers look hard enough. Now, the chance discovery of faint light captured by the Atacama Large Millimeter Array (ALMA) in Chile has revealed the existence of one such “cosmic Yeti,” according to a press release. 

University of Arizona astronomer Christina Williams noticed a shimmering splash of light in observations from the ALMA radio telescope in an area where nothing had been seen before.

“It was very mysterious because the light seemed not to be linked to any known galaxy at all,” Williams says in a statement. “When I saw this galaxy was invisible at any other wavelength, I got really excited because it meant that it was probably really far away and hidden by clouds of dust.”

The team estimates that the light from the galaxy took 12.5 billion years to reach Earth, meaning that it is an extremely rare glimpse of a galaxy that formed less than 2 billion years after the Big Bang.

The light detected, however, isn’t from the galaxy itself. Researchers suspect that ancient galaxy has 100 billion stars, which is about the same as the Milky Way. It’s also possible that it forms new stars at a rate 100 times faster than our corner of the universe. Clouds of dust conceal all that starlight, but ALMA was able to detect the faint glow from dust particles. The team’s findings are documented in The Astrophysical Journal..

This “monster” galaxy, however, is more than just a cool find. It also helps to answer some big questions in cosmology. Most of the large galaxies astronomers have observed from the early universe reached maturity very quickly—when the universe was just about 10 percent of its current age of about 13.8 billion years old, give or take a billion. For that to happen, those mature galaxies had to come from much larger monster precursor galaxies, something researchers have never observed. But the so-called monster galaxy and other recent observations may finally solve the mystery. 

“Our hidden monster galaxy has precisely the right ingredients to be that missing link because they are probably a lot more common,” says Williams in a statement.

The team found theirs by looking at an incredibly tiny slice of the sky, about one-hundredth of the width of the full moon. Study coauthor Kate Whitaker, an astronomer at the University of Massachusetts Amherst, thinks there could be a lot more galaxies like it out there. 

“These otherwise hidden galaxies are truly intriguing; it makes you wonder if this is just the tip of the iceberg, with a whole new type of galaxy population just waiting to be discovered,” she says in another press release.

In fact, other massive star-forming galaxies were spotted earlier this year. In August, another team using the ALMA telescope reported in the journal Nature that they had located 39 galaxies that formed before the universe was two billion years old. Those seem to be embedded in a dark matter halo, making them difficult to observe directly.

Both teams are awaiting the launch of the James Webb Space Telescope currently scheduled to lift off in 2021. That scope should be powerful enough to penetrate the dust and answer the questions swirling around these galaxies. 

“JWST will be able to look through the dust veil so we can learn how big these galaxies really are and how fast they are growing, to better understand why models fail in explaining them,” Williams says.