Japanese researchers have been able to study the nature of dark matter surrounding galaxies as they were twelve billion years ago, pushing back several billion light-years the observation of this mysterious substance that dominates the universe. Their work has been published in Physical Review Letters.
Dark Matter and Gravitational Lensing
Consider these two points first. Let’s start with dark matter. We know that the speed at which a star must move to stay in its orbit depends on the gravitational force pulling it towards the center of its galaxy, and therefore on the latter’s mass. Over time, we realized that the amount of visible matter available to keep the stars in our galaxy in their orbits was insufficient. Therefore, the existence of a form of extraneous substance capable of explaining this movement has been suggested. This matter which does not emit, absorb or reflect any light is called “dark matter”. It is now assumed that he Composes about 26.8% of the universe.
Let’s continue with the gravitational lensing effect. We know that gravity (and therefore mass) distorts the very fabric of spacetime. The more massive an object, the greater the curvature of the fabric of spacetime. Under these conditions, light from a background galaxy passing through this area will inevitably be present Curved, but widened. This effect therefore makes it possible to visualize distant galaxies that would otherwise be invisible.
Back to our research. During their analyzes aimed at defining the true nature of dark matter, researchers sometimes rely on the phenomenon of gravitational lensing. Ideally, the gravitational pull of a foreground galaxy, with its dark matter, will distort the light of a background galaxy. The greater the amount of dark matter, the greater the distortion. Scientists can therefore measure the amount of dark matter around the foreground galaxy (“lens” galaxy) from this distortion.
The events after the Big Bang
Beyond a certain point, galaxies become incredibly faint. Therefore, the further back you go, the less effective the strategy will be. Unable to detect source galaxies far enough away to measure the distortion of their light, most previous studies have only been able to analyze dark matter from eons ago. Eight to ten billion years at most. These constraints therefore leave open the question of the Big Bang occurring about 13.7 billion years ago and the distribution of dark matter during this period.
To overcome these challenges, a team led by Nagoya University’s Hirono Miyatake relied on a different source: microwaves from the cosmic microwave background (CMB), the radiation remnant from the Big Bang. Recall that according to the Standard Model of cosmology, this radiation was emitted approx 380,000 years after the Big BangWhen the observable universe was still much smaller, denser and hotter than it is today.
For this work, the researchers first used data from the Subaru Hyper Supreme-Cam Survey (HSC) observations to identify 1.5 million “lens galaxies” They appear as they were before Twelve billion years, just 1.7 billion years after the beginning of the universe. Using the Planck satellite from the European Space Agency (ESA), the team then measured how the dark matter surrounding these galaxies distorts these famous microwaves.
This is the first time this mysterious but oh so important substance has been detected at such a distance.
A modified model?
One of the most interesting findings of this study relates to the clumping of this material. According to the standard theory of cosmology, the lambda-CDM model, subtle fluctuations in the cosmic microwave background create pools of dense matter by gravitationally pulling on surrounding matter. This dense region has the effect of creating homogeneous clusters that form stars and galaxies. Group results suggest their additive measure Lambda-CDM is lower than predicted by the model.
If the finding is confirmed, it would suggest that you may have the entire model malfunctioning over time. A more refined model could then give astronomers greater insight into the nature of dark matter.
Note that these works are not finished. The researchers looked at only a third of the data from the Subaru Hyper Supreme-Cam survey. The next step will be to analyze all the data, which could potentially provide a more precise measure of the distribution of dark matter.