Astronomers have uncovered the footprints of a previously unknown monster galaxy in the early Universe.

The discovery, which is reported in a paper in The Astrophysical Journal, provides new insights into the massive galaxies, which are often regarded by the scientific community as folklore, due to a lack of evidence of their existence. A copy of the paper is available on the pre-print server arXiv.

Using the Atacama Large Millimeter Array (ALMA), lead author Christina Williams from the University of Arizona Steward Observatory, US, noticed a faint light blob that seemed to be coming from nowhere.

“It was very mysterious because the light seemed not to be linked to any known galaxy at all,” she says. “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.”

And far away it was.

The researchers estimate that the signal took 12.5 billion years to reach Earth, which gives them a glimpse into the Universe in its infancy.

They suggest the observed emission is caused by the warm glow of dust particles which is heated by the stars forming deep inside a young galaxy. The giant clouds of dust conceal the light of the stars themselves, rendering the galaxy completely invisible.

“We figured out that the galaxy is actually a massive monster galaxy with as many stars as our Milky Way but brimming with activity, forming new stars at 100 times the rate of our own galaxy,” says co-author Ivo Labbé, from Swinburne University of Technology in Australia.

The authors say the discovery of this massive galaxy may be the answer to a long-standing question in astronomy.

Previous studies have found that some of the biggest galaxies grew quickly, however this result is yet to be understood theoretically. Likewise, smaller galaxies in the early Universe have been observed growing very quickly – but weren’t fast enough to solve the astronomy puzzle.

However, Williams is hopeful that this discovery will lead to some understanding of galaxy formation.

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

Williams adds that the researchers are eagerly awaiting the launch of NASA’s James Webb Space Telescope (JWST), which is scheduled for March 2021, to investigate monster galaxies in more detail.

“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.”

This story originally appeared at the cosmos magazine.