One of science’s greatest unsolved mysteries is twisted into our universe. Where is all the dark matter? What exactly is all this dark matter?
We all know it’s there.
Our physics predicts that everything inside galaxies, including the Milky Way, will be flung outward like horses on an unhinged merry-go-round. But, obviously, that is not the case. We, the sun, and the Earth are all securely anchored. As a result, scientists hypothesize that something resembling a halo must surround galaxies to keep them from collapsing.
Dark matter refers to whatever exists within those boundaries. We can’t see it, we can’t feel it, and we’re not even sure it’s the same thing. It’s the definition of elusive. We only have evidence that dark matter exists.
Despite our inability to see or touch the material, experts have devised novel methods for determining the effects it has on our universe. After all, we discovered the existence of dark matter by observing how it holds galaxies together in the first place.
On Monday, scientists took advantage of this principle, announcing remarkable new findings about dark matter. They discovered a deep space zone of previously unstudied dark matter halos, each located around an ancient galaxy, dutifully protecting it from living out a merry-go-round nightmare, using a toolkit made up of warped space, cosmic residue left over from the Big Bang, and powerful astronomy instruments.
According to a study published in Physical Review Letters, these whirls date back 12 billion years or just under two billion years after the Big Bang. According to the authors, this makes them the youngest dark matter rings ever studied by humanity and could be the prelude to the next chapter of cosmology.
“I was happy that we opened a new window into that era,” Nagoya University’s Hironao Miyatake, the study’s author, said in a statement. “Things were very different 12 billion years ago. There are more galaxies in the formation process than now, and the first galaxy clusters are forming as well.”
Warped space, you say? Is there cosmic residue?
Yes, you read that right. Allow me to explain.
When Albert Einstein coined his famous theory of general relativity more than a century ago, one prediction he made was that super strong gravitational fields generated by massive amounts of matter would literally warp the fabric of space and time or spacetime. He was proven to be correct. Today, physicists use the concept to study very distant galaxies and other phenomena in the universe using a technique known as gravitational lensing. It works in this manner.
Consider two galaxies. Galaxy A is in the distance, and Galaxy B is in the foreground.
Essentially, as light from galaxy A passes through galaxy B to reach your eyes, its luminescence is distorted by B’s matter, whether dark or not. This is good news for scientists because such distortion frequently magnifies distant galaxies like a lens.
Furthermore, you can use this light warp to perform a sort of reverse calculation to determine how much dark matter surrounds galaxy B. If galaxy B contained a lot of dark matter, you’d see a lot more distortion than you’d expect from visible matter (the stuff we can see). However, the distortion would be much closer to your prediction if there wasn’t so much dark matter. This system has worked fairly well, but there is one caveat.
Standard gravitational lensing can only detect dark matter in the vicinity of galaxies that are 8 billion to 10 billion light-years away at most.
This is because, as you look deeper into the universe, visible light becomes increasingly difficult to interpret, eventually transforming into infrared light, which is completely invisible to human eyes. (This is why NASA’s James Webb Space Telescope is so significant.) It’s our best chance of capturing the faintest, most indistinguishable light from the distant cosmos.) However, this means that visible light distortion signals for dark matter studies become far too faded after a certain point, making it difficult to analyze the hidden stuff.
Miyatake figured out a way around the problem.
Perhaps we can’t detect dark matter using standard light distortions, but what if there’s another type of distortion we can see? As it turns out, there is microwave radiation from the Big Bang. It’s basically Big Bang heat remnants, also known as cosmic microwave background, or CMB, radiation.
“Have you looked at the dark matter around distant galaxies?” Masami Ouchi, a cosmologist at the University of Tokyo and study co-author, said in a statement. “It was an insane idea. Nobody believed we could pull it off. However, after I gave a talk about a large distant galaxy sample, Hironao approached me and said that the CMB could be used to look for dark matter around these galaxies.”
Miyatake’s goal was to observe how dark matter gravitationally lensed the first light in our universe.
Piecing together the Big Bang
“Most researchers use source galaxies to measure dark matter distribution from the present to 8 billion years ago,” said Yuichi Harikane, an assistant professor at the University of Tokyo and study co-author. “We could, however, look further back in time because we used the more distant CMB to measure dark matter. For the first time, we measured dark matter from the beginning of the universe.”
The new study team gathered data from the Subaru Hyper Suprime-Cam Survey observations to arrive at their conclusions.
This led to the discovery of 1.5 million lensed galaxies – a slew of hypothetical galaxy dating back 12 billion years. They then used data from the European Space Agency’s Planck satellite to study Big Bang microwave radiation. When it all comes together, the team will be able to determine whether and how the lensed galaxies distorted the microwaves.
“This result provides a very consistent picture of galaxies and their evolution, as well as dark matter in and around galaxies, and how this picture evolves over time,” Neta Bahcall, a Princeton University professor of astrophysical sciences and study co-author, said in a statement.
Notably, the researchers highlighted their study’s discovery that dark matter from the early universe does not appear to be as clumpy as our current physics models suggest. This could change our current understanding of cosmology, particularly theorems based on what’s known as the Lambda-CDM model.
“Our conclusion remains uncertain,” Miyatake said. “But, if true, it would imply that the entire model is flawed as you go back in time. This is exciting because, if the result holds after the uncertainties are removed, it may indicate an improvement in the model, which may provide insight into the nature of dark matter itself.”
Next, the research team plans to investigate even earlier regions of space by utilizing data from the Vera C. Rubin Observatory’s Legacy Survey of Space and Time.
“LSST will enable us to observe half of the sky,” Harikane explained. “I don’t see why we couldn’t see the distribution of dark matter 13 billion years ago.”
