Dark matter from billions of years ago finally detected by scientists

Dark matter from billions of years ago has finally been detected by scientists on Earth.

Researchers were able to investigate the nature of dark matter that surrounded galaxies as they were 12 billion years ago. That is billions of years earlier than we had ever been able to see before.

Scientists hope the breakthrough findings could reveal the secrets of the still mysterious dark matter that makes up a significant part of our universe but is largely unknown.

It has already offered tantalising clues about the history of our cosmos. Researchers say the findings suggest that the fundamental rules of the universe were different in its earliest times.

As its name suggests, scientists are not able to see dark matter directly, because it does not emit light. Instead, scientists usually watch as light travels through the galaxies they want to investigate, measuring how it travels – the more it is distorted, the more dark matter there is.

However, the most distant galaxies – which we see as they existed billions of years ago – are too faint for this technique to work. The distortion cannot be detected properly and the dark matter has remained impossible to analyse.

That left scientists unable to research dark matter from more than around 10 billion years ago. The time before that and the beginning of the universe, 13.7 billion years ago, remained impossible to understand.

Now scientists say they have overcome that problem by using a different source: the microwaves that were released by the Big Bang. The team measured how those microwaves were distorted, rather than light, and in doing so were able to see the dark matter from the beginnings of the cosmos, looking at galaxies soon after they formed.

“Most researchers use source galaxies to measure dark matter distribution from the present to eight billion years ago”, added Assistant Professor Yuichi Harikane of the Institute for Cosmic Ray Research, University of Tokyo. “However, we could look further back into the past because we used the more distant CMB to measure dark matter. For the first time, we were measuring dark matter from almost the earliest moments of the universe.”

The results showed a range of surprises, including showing the way the dark matter clumped up in the early universe. Theory suggests that the dark matter should stick together and form lumps in the cosmos – but there was much less of that than predicted.

“Our finding is still uncertain”, said Hironao Miyatake from Nagoya University, who led the team. “But if it is true, it would suggest that the entire model is flawed as you go further back in time. This is exciting because if the result holds after the uncertainties are reduced, it could suggest an improvement of the model that may provide insight into the nature of dark matter itself.” 

An article describing the findings is published in Physical Review Letters.