Treasure trove of new galaxies defies current models of the universe

8 Aug 2019

Some of the 66 radio telescope antennas that make up ALMA. Image: Kohno et al/PA

The discovery of ‘previously invisible’ galaxies is important as their existence undermines the rules of the universe that have already been set out.

The mystery of what happened a long time ago, in a galaxy far, far away, may finally have some light shed on it. Astronomers have discovered what they say is a treasure trove of previously unknown massive ancient galaxies. It is the first multiple discovery of its kind and such an abundance of this type of galaxy defies current models of the universe, researchers said.

The study published in the Nature journal sets out that the galaxies are also intimately connected with supermassive black holes and the distribution of dark matter. Researcher Tao Wang from the University of Tokyo said: “This is the first time that such a large population of massive galaxies was confirmed during the first two billion years of the 13.7-billion-year life of the universe.

“These were previously invisible to us. This finding contravenes current models for that period of cosmic evolution and will help to add some details, which have been missing until now.”

Invisible to the human eye, the light from the 39 galaxies was detected using the combined power of multiple astronomical observatories around the world.

Hard to spot

Prof 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. I have a long history with that facility and so knew it would deliver good results.”

Scientists say that despite these galaxies being the largest of their time, the light from them is not only weak but also stretched due to their immense distance. As the universe expands, light passing through becomes stretched, so visible light becomes longer, eventually becoming infrared.

Image of the huge cluster of ancient galaxies and close-up photos on the right.

Ancient galaxies from the study are visible to ALMA (right) but not to Hubble. Image: Wang et al/PA

Astronomers are able to calculate how far away something is by analysing the amount of stretching. This also indicates how long ago the light was emitted. Another reason these galaxies appear so weak is because larger galaxies, even in the present day, tend to be shrouded in dust, which obscures them more than their smaller galactic siblings.

Wang said: “It was tough to convince our peers these galaxies were as old as we suspected them to be. Our initial suspicions about their existence came from the Spitzer Space Telescope’s infrared data.

“But ALMA has sharp eyes and revealed details at submillimetre wavelengths, the best wavelength to peer through dust present in the early universe. Even so, it took further data from the imaginatively named Very Large Telescope in Chile to really prove we were seeing ancient massive galaxies where none had been seen before.”

Uncovering ‘primordial beasts’

The bigger a galaxy, the bigger the supermassive blackhole at its heart, said the scientists. So the study of the new galaxies and their evolution will tell researchers about the evolution of their blackholes too.

“Massive galaxies are also intimately connected with the distribution of invisible dark matter. This plays a role in shaping the structure and distribution of galaxies. Theoretical researchers will need to update their theories now,” said Kohno.

The researchers also set out how the newly discovered galaxies differ from the Milky Way.

Wang said: “For one thing, the night sky would appear far more majestic. The greater density of stars means there would be many more stars close by appearing larger and brighter.

“But conversely, the large amount of dust means farther-away stars would be far less visible, so the background to these bright close stars might be a vast dark void.”

He added that he was eager for upcoming observatories such as the space-based James Webb Space Telescope to show us “what these primordial beasts are really made of”.

– PA Media