Dark matter is five times more prevalent in the Universe by mass than normal matter, and it's the stuff you and I are made of. Even though we don't know what it's made of, we can see its effects. Dark matter has an effect on how the universe rotates and moves.
We can see its effects by looking at it through a lens. Space warps because of mass's gravity. The mass of the foreground galaxy distorts the image of the background one. It can look smeared, bent, or even duplicated into more than one image. The name is derived from the fact that the foreground galaxy has gravity.
The mass of normal matter can be measured using the light from the lensing galaxy. We can measure how much it distorts objects farther away. The amount of darkness it harbors is different. The method has worked well in the past.
There is a problem. We don't have enough background galaxies to use because individual galaxies are too small to see. This isn't convenient. The speed of light is finite so we want to see as far away as possible. The younger we are, the more we see it being.
We want to know what the distribution of dark matter was like when the Universe was young, because we think it drew normal matter to those clumps. By knowing what dark matter was like in the past, we can better understand how the universe came to be. It takes time for the universe's largest structures to form. The shape and size of the universe can be determined by looking at clusters.
If we don't have very distant galaxies to look at, how do we do that? Don't use lensed galaxies to measure dark matter, that's what a team of astronomer dreamed up. The background glow of the Big bang can be used.
The birth of the Universe was a big deal. The fireball cooled as the universe grew. It became transparent when it became big and low density. The Cosmic Microwave Background Radiation has been shifted into the microwave part of the spectrum by the expansion of the universe. The glow was very similar to what you would see in the sky. It will clump up a bit because of the lensing.
The data from the European Space Agency's Planck satellite, which measured that glow to high precision, was used by the astronomer to map it against a survey of a lot of galaxies. The astronomer looked at the distances of 1,473,106 galaxies and found them to be reliable. The light from these galaxies took 12 billion years to reach us, so we can see them as far away as 1.8 billion years after the birth of the universe.
They were able to determine the mass of the galaxies from the amount of light they were able to see. On average, they had dark matter haloes that were 300 billion times the mass of the sun. Our own Milky Way has about 700 billion solar mass. We can see the distant galaxies as they were when they were young.
Something very interesting was found by them. The distribution of matter in the early Universe is a little lumpiness because the Cosmic Background Radiation isn't perfect. These clumps were the beginning of the universe. The standard model predicts a certain amount of clumpiness, but the new measurement get a slightly smaller value. It is close, but not quite the same, which suggests that there may be more going on in the universe than we think.
It is very tentative. It is difficult to say if the disagreement is real or not because the new measurement have a lot of uncertainty. When the big survey of the sky is completed, it will cover three times as much sky as was used in the study. The uncertainties should be hammered down a bit. The measurement of the microwave background radiation will be improved in the future.
The first reliable measurement of the background radiation is only a few decades old, and the method for getting the galaxy mass has only been around for a few decades. A new method is being used to figure this out. We keep refining science until we understand it better and make sense. It isn't finished even then. There may be more that needs to be figured out to make the measurement better.
We are in the middle of the recipe, trying to write down the basics of how to cook the Universe. We're making progress. We will continue to understand how the universe came to be.