Researchers from the Nagoya University in Japan have investigated the nature of dark matter surrounding galaxies seen as they were 12 billion years ago, billions of years further back in the past than ever before.
Reported first by EurekaAlertthe study offers a strange possibility that the fundamental rules of cosmology could be different when looking at the early history of the universe.
Why this matters
Looking so far in the past is difficult. Today due to the finite speed of light, we see distant galaxies not the way they appear today, but actually how they appeared billions of years ago. Even more challenging was observing dark matter that doesn’t emit light.
Take for instance a distant source galaxy, further away than the galaxy whose dark matter a particular researcher is trying to investigate. The gravitational pull of the foreground galaxy along with its dark matter distorts the surrounding space and time, as predicted by Einstein’s theory of general relativity.
With the light from the source traveling through this distortion, it bends, while also altering the shape of the galaxy. More dark matter translates to increased distortion, which allows scientists to measure the amount of dark matter around the foreground galaxy from the distortion.
However, after a certain point, scientists come across a problem. The galaxies in the deepest parts of the universe are incredibly faint. Thus, the farther from Earth researchers look, the less effective this technique becomes. The distortion is subtle but also complicated to detect in most cases, thus many background galaxies are crucial to detecting the signal.
Several previous studies have remained stuck at these thresholds. With no ability to detect enough distant source galaxies to measure the distortion they could only analyze the dark matter from no more than 8 to 10 billion years ago. These left open the mysteries of dark matter between this time and 13.7 billion years ago, around the beginning of our universe.
To overcome this, a research team led by Hiroano Miyatake from Nagoya University in collaboration with the University of Tokyo, the National Astronomical Observatory of Japan and Princeton University made use of a different source of background light — the microwaves released from the big bang itself.
They used the data from observations of the Subaru Hyper Suprime Cam Survey where the team was able to identify 1.5 million lens galaxies using visible light, selected to be seen 12 billion years ago.
In order to overcome the lack of galaxy light even further away, they employed microwaves from the cosmic microwave background (CMB), the radiation residue from the Big Bang. Looking at the microwaves observed by ESA’s Planck Satellite, the team calculated how the dark matter around lens galaxies distorted the microwaves.
Assistant Professor Yuichi Harikane of the Institute for Cosmic Ray Research, University of Tokyo, explained, “Most researchers use source galaxies to measure dark matter distribution from the present to eight billion years ago. 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.”
Post a preliminary analysis, researchers soon realised that they had a large enough sample to detect the distribution of dark matter, Fusing the large distant galaxy sample and the lensing distortions in CMB, they detected dark matter even further back in time, from 12 billion years ago. This was around 1.7 billion years after the beginning of the universe, which actually isn’t that long.
Hironao Miyatake added, “Our finding is still uncertain. 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.”
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