Scientists have probed the most distant dark matter halo ever studied using gravitational lensing, a phenomenon once predicted by Albert Einstein.
Why it matters
What they found by observing these rings could affect the known model of cosmology.
In our universe lies one of the greatest unsolved mysteries of science. Where is all the dark matter? What is all dark matter?
We know it’s there.
Galaxies, including the Milky Way, spin so fast that our physics predicts that everything inside should be flung out like a horse on an unsuspended merry-go-round. But obviously that’s not happening. You, me, the sun and the earth are safely anchored. Therefore, scientists theorize that something – probably in the form of a halo – must surround the galaxies to protect them from disintegration.
Anything that contains these boundaries is simply called dark matter. We don’t see it, we don’t feel it, and we don’t even know if it’s one homogeneous thing. We only know that dark matter exists. It is the epitome of elusiveness.
But despite our inability to see or touch the material itself, experts have interesting ways of identifying the effects it has on our universe. After all, we inferred the presence of dark matter primarily by noticing how it holds galaxies together.
And on Monday, scientists who took advantage of this principle announced their remarkable new findings. With a toolkit made up of warped space, cosmic debris left over from the Big Bang, and some powerful astronomical instruments, they discovered a deep space zone of previously unexplored dark matter halos—each one surrounding an ancient galaxy and dutifully protecting it from living a merry life. -bypass the nightmare.
Those beliefs date back, according to a new study on the find published in Physical Review Letters 12 billion years ago, less than two billion years after the Big Bang. That could very well make them the youngest rings of dark matter ever studied, the study authors suggest, and potentially a prelude to the next chapter of cosmology.
“I was happy that we opened a new window into this era,” Hironao Miyatake of Nagoya University and an author of the study said in a statement. “12 billion years ago, things were very different. You see more galaxies that are in the process of forming than today; even the first clusters of galaxies are starting to form.”
Wait, warped space? A cosmic remnant?
Yes, you read that right. Let’s explain it.
More than a century ago, when Albert Einstein created his famous theory of general relativity, one of his predictions was that super-strong gravitational fields coming from massive amounts of matter would literally warp the fabric of space-time, or space-time. Turns out he was right. Physicists today exploit this concept by using a technique called gravitational lensing to study very distant galaxies and other phenomena in space. It kind of works like this.
Imagine two galaxies. Galaxy A is in the background and B is in the foreground.
Basically, when light coming from galaxy A passes through galaxy B to reach your eyes, that luminescence is distorted by B’s matter – dark or not. But this is good news for scientists, because such distortions often increases distant galaxies, something like a lens.
Furthermore, there is a kind of back-calculation you can do with this light warp to find out how much dark matter surrounds galaxy B. If galaxy B held lots of dark matter, you would see a lots of greater distortion than expected from the visible matter inside. But if it didn’t have that much dark matter, the bias would be much closer to your prediction. This system worked quite well, but it has one caveat.
Standard gravitational lensing only allows researchers to identify dark matter around galaxies that are at most 8 to 10 billion light-years away.
This is because as you look deeper and deeper into space, visible light becomes more and more difficult to interpret and eventually even turns into infrared light, which is completely invisible to the human eye. (Thereforeis such a big deal—it’s our best attempt to pick up the faintest, most invisible light coming from the distant universe.) But that means that the visible-light bias signals for dark matter studies are too faint beyond a certain point to help us analyze the hidden stuff.
Miyatake came up with a solution.
We may not be able to notice the standard distortions of light to detect dark matter, but what if there is another type of distortion that we can see? As it turns out, there is: microwave radiation released from none other than the Big Bang. They are largely remnants of the heat of the Big Bang, formally known as the cosmic microwave background or CMB radiation.
“See dark matter around distant galaxies?” Masami Ouchi, a cosmologist at the University of Tokyo and co-author of the study, said in a statement. “It was a crazy idea. No one realized we could do it. But after I talked about a large sample of a distant galaxy, Hironao came to me and said it was possible to look at the dark matter around these galaxies using the CMB.” ”
Essentially, Miyatake wanted to observe how dark matter gravitationally lensed the first light of our universe.
Collecting the pieces of the big bang
“Most researchers use source galaxies to measure the distribution of dark matter from the present to 8 billion years ago,” Yuichi Harikane, an assistant professor at the University of Tokyo and co-author of the study, said in a statement. “However, we could 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 almost the earliest moments of the universe.”
To arrive at their results, the new study team first collected data from observations made by the Subaru Hyper Suprime-Cam Survey.
This led them to identify 1.5 million lenticular galaxies – the hypothetical B galaxy cluster – that can be traced back to 12 billion years ago. They then called in information from the European Space Agency’s Planck satellite about the big bang’s microwaves. Put it all together, and the team could learn whether and how these lensing 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 that picture evolves over time,” said Neta Bahcall, professor of astrophysical sciences at Princeton University and co-author of the study. , he said in a statement.
In particular, the researchers emphasized that their study found that dark matter from the early universe does not appear to be as coarse as our current physics models suggest. This piece could modify what we currently believe about cosmology, mainly the theorems rooted in what is called the Lambda-CDM model.
“Our finding is still uncertain,” Miyatake said. “However, if true, it would suggest that the whole 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 improvements to the model that may provide insight.” into the nature of dark matter itself.”
And next up, the study team wants to explore even earlier regions of the universe by tapping into information from the Vera C. Rubin Observatory’s Legacy Survey of Space and Time.
“The LSST will allow us to observe half the sky,” Harikane said. “I don’t see any reason why we couldn’t see the distribution of dark matter 13 billion years ago.”