Scientists discover the oldest dark matter ever observed in the Universe

What little we know about dark matter comes from calculations based on the glow of surrounding galaxies. However, the farther we look, the more the starlight fades, making it harder to see the subtle influence of this most mysterious force.

Now, a collaboration between astronomers from Japan and the United States has found a different way to shed light on the distant darkness, by studying how dark masses of dark matter distort the background glow of the cosmos.

Like photos dropped from a moving car, the entire history of our Universe is spread out over the vastness of space. To see a succession of standout moments, all we need to do is keep looking further down the highway.

Unfortunately, the growing expansion of everything hasn’t been kind to these older snaps, stretching their starlight palettes until they’re so depleted of energy that they appear to us as little more than glowing embers.

It’s a shame we can’t see them as they are. If these early galaxies are anything like the ones we’ll see much later in the Universe’s timeline, their structures should be influenced by pockets of gravity produced by…well, we haven’t a clue.

It is called dark matter only because it radiates no information that tells us anything about its nature. It’s probably some sort of particle-like mass with few properties, much like a neutrino. There’s an outward chance that this reflects something we’ve misunderstood about the formation of space and time.

In short, we still do not have a concrete theory on the place of this phenomenon in existing physics. So getting an accurate measure of what those super ancient dark matter halos looked like would at least tell us if they changed over time.

We cannot estimate their total mass – both invisible and glowing – by measuring their pale light. But it is possible to use the way their collective mass distorts starlight passing through their surrounding space.

This lensing technique works quite well for large groups of galaxies seen 8 to 10 billion years ago. However, the further back we want to see, the less stellar radiation there is in the background to analyze distortions.

According to Nagoya University astrophysicist Hironao Miyatake and his colleagues, there is another source of light that we could use, called the cosmic microwave background (CMB).

Think of the CMB as the first photo of the newborn cosmos. The echo of light emitted when the Universe was around 300,000 years old now pervades space as faint radiation.

Scientists are using subtle patterns in this background hum to test all sorts of hypotheses about critical early phases in the evolution of the Universe. Using it to estimate the average mass of distant galaxies and the distribution of dark matter halos around them was a first, however.

“It was a crazy idea. Nobody realized we could do that,” says Masami Ouchi, an astrophysicist from the University of Tokyo.

“But after giving a lecture on a large sample of distant galaxies, Hironao came to me and said that it might be possible to observe dark matter around these galaxies with the CMB.”

Hironao and his colleagues focused on a special set of distant star-forming objects called Lyman-break galaxies.

Using a sample consisting of nearly 1.5 million of these objects collected as part of the Hyper Suprime-Cam Subaru Strategic Program survey, they analyzed the microwave radiation patterns seen by the satellite. Planck from the European Space Agency.

The results provided the researchers with a typical halo mass for galaxies nearly 12 billion years ago, a time quite different from what we see closer to home today.

According to standard cosmological theory, the formation of these early galaxies was largely determined by fluctuations in space exaggerating the clumping together of matter. Interestingly, these new findings about early galactic masses reflect less material aggregation than current preferred models predict.

“Our discovery is still uncertain,” says Miyatake. “But if true, that would suggest that the whole model is flawed as you go further back in time.”

Revisiting existing models of how freshly baked elements came together to form the first galaxies could reveal gaps that could also explain the origins of dark matter.

As faded as the Universe’s baby photos are, it’s clear they still have quite a story to tell about how we’ve become.

This research was published in Physical examination letters.

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