Primordial Beasts: 39 Ancient, Massive, Invisible Galaxies That Defy Theories of Early Universe Discovered

Dozens of massive "invisible" galaxies from the early universe have been discovered by scientists. These "primordial beasts," which cannot be seen with the Hubble Space Telescope, defy current models of the universe, with no major theories accounting for such a rich population of dark, star-forming massive galaxies.

Hubble, which was launched in 1990, has offered astronomers an unparalleled view of the universe. However, it cannot see everything.

Tao Wang, from the Institute of Astronomy at the University of Tokyo, and colleagues believed there were galaxies that were invisible to Hubble—their light was too stretched and they were shrouded in dust, making them appear dark.

In a statement, study co-author Kotaro Kohno explained: "The light from these galaxies is very faint with long wavelengths invisible to our eyes and undetectable by Hubble. So we turned to the Atacama Large Millimeter/submillimeter Array (ALMA), which is ideal for viewing these kinds of things."

Researchers discovered a huge population of massive galaxies that existed in the first two billion years after the Big Bang—about 13.8 billion years ago. "These were previously invisible to us," Wang said in a statement. "This finding contravenes current models for that period of cosmic evolution and will help to add some details, which have been missing until now."

hubble vs alma
Alma was able to detect galaxies that were invisible to Hubble. The University of Tokyo/CEA/NAO

In their study, published in Nature, the team notes that our current understanding of how stars formed in the universe's infancy is based on extremely active star-forming "starburst" galaxies that produce about 1,000 Sun-sized stars per year. But this is known to under-represent massive, dust-rich galaxies, raising questions about how many of these may be out there.

The first found 63 extremely red objects in infrared images taken with the Spitzer Space Telescope. These objects were then probed with ALMA, with the team finding 39 of them were massive, star forming galaxies that produce stars 100 times more efficiently than the Milky Way, spewing out around 200 per year.

"Residing in the most massive dark matter haloes at their redshifts, they are probably the progenitors of the largest present-day galaxies in massive groups and clusters," the team write.

Wang added: "Star formation in the dark galaxies we identified is less intense, but they are 100 times more abundant than the extreme starbursts. It is important to study such a major component of the history of the universe to comprehend galaxy formation."

It is their abundance that current models of the universe cannot account for. The team estimate there to be 530 objects in every square degree of the sky—well beyond what theories and simulations predict from models of the evolution of the early universe. Findings indicate massive galaxies were created during the first billion years of the universe's existence.

Wang said far more research will be needed to understand these galaxies: "These gargantuan galaxies are invisible in optical wavelengths so it's extremely hard to do spectroscopy, a way to investigate stellar populations and chemical composition of galaxies," he said. "ALMA is not good at this and we need something more. I'm eager for upcoming observatories like the space-based James Webb Space Telescope to show us what these primordial beasts are really made of."

invisible galaxies
Artist impression of the "invisible" galaxies. NAO