A collaborative study has investigated the nature of dark matter surrounding galaxies as they appeared 12 billion years ago, which is billions of years further older than dark matter studied before. The research findings open up the possibility that fundamental cosmological rules may differ when examining the early history of the universe. The findings have been published in Physical Review Letters.
Since distant galaxies are mostly millions of light years away. We see distant galaxies not as they are today but as they were billions of years ago. Seeing something that happened a long time is particularly challenging due to how distant such objects are from us. It is even more challenging to observe dark matter, which does not emit light.
When observing the light of distant galaxies, the mass of the galaxy and the dark matter within it distorts the surrounding space and time, as predicted by Einstein’s theory of general relativity. This distortion in space and time bends the light that travels through it, thereby changing the apparent shape of the galaxy. Scientists can measure the amount of dark matter using this distortion.
But beyond a certain point, scientists encounter a problem. The light from really distant galaxies is incredibly faint. As a result, this technique gets less effective the further away a galaxy is since the lensing distortion is subtle and difficult to detect in most cases. Most previous studies have been unable to analyse dark matter from more than eight to ten billion years ago. This meant that the distribution of dark matter between this time and when the universe was formed around 13.8 billion years ago was unknown.
The research team led by Hironae Miyatake from Nagoya University used a different source of background light to observe this distortion: the microwaves released from the Big Bang itself. They first used data from the Subaru Hyper Suprime-Cam Survey (HSC) to identify 1.5 million lens galaxies (galaxies that distort light coming from behind them)
The team then took advantage of the cosmic microwave background (CMB), the residual radiation from the Big Bang. They used microwave observations by the European Space Agency’s Planck satellite to measure how the dark matter around the lens galaxies distorted the microwave radiations that came from the big bang.
The research helped scientists make an exciting discovery related to the “clumpiness” of dark matter. According to the Lambda-CDM model, the Standard Model of Cosmology, CMB fluctuations form “clumps” of densely packed matter that attract surrounding matter through gravity. Even though it is not conclusive, the new research indicates that the measurement was lower than predicted by the Lambda-CDM model.
“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,” said Miyatake, in a press statement. The next step for the research is to use more extensive and sophisticated datasets to allow for a more precise measurement of dark matter distribution.