The most distant dark matter ever discovered dates back 12 billion years
But this method only works when the source galaxy is bright enough to illuminate the lens galaxy. And because extremely distant galaxies are extremely faint, astronomers have so far been unable to assess dark matter in galaxies from around 8 to 10 billion years ago. This left them largely in the dark about the true structure of the early universe.
In an effort to overcome this hurdle, a team of astronomers recently modified the approach. Instead of using two galaxies, they chose to use a more distant light source instead of a source galaxy: the Cosmic Microwave Background (CMB), emitted when the universe was only 300,000 years old. .
“It was a crazy idea,” Masami Ouchi, study author and astronomer at the University of Tokyo, said in a press release. “Nobody realized we could do this.”
“Most researchers use source galaxies to measure the distribution of dark matter from the present to 8 billion years ago,” added Yuichi Harikane, study author and astronomer at the University of Tokyo. “However, we were able to look further into the past because we used the more distant CMB to measure dark matter. For the first time, we have been measuring dark matter since almost the earliest moments of the universe.
Lighting up dark matter
To employ their new approach, the astronomers selected 1.5 million galaxies – all seen as they were around 12 billion years ago – to collectively serve as a gravitational lens. And with the more distant CMB serving as a background light source, the team was able to measure how dark matter was dispersed around these lens galaxies.
“I was happy that we opened a new window to this era,” said Hironao Miyatake, another study author and astronomer at Nagoya University, in a press release. “Twelve billion years ago things were very different.”
According to the team, their results could challenge popular theories of cosmology, including the idea that tiny variances in the CMB are what initially led to the first clumps of matter, which eventually formed into stars and in galaxies. It turns out, according to the team, that the universe was much more homogeneous in its early years than previously thought.
“Our discovery is still uncertain,” Miyatake said in a press release. “But if true, that would suggest the whole model is flawed as you go further back in time. That’s exciting because if the result holds after reducing uncertainties, that might suggest improvement. of the model that could provide insight into the nature of dark matter itself.
Ultimately, the team says their approach will provide astronomers with more accurate measurements of the amount and distribution of dark matter in ancient galaxies. It will also allow astronomers to explore other aspects of the early universe.
“One of the strengths of observing the universe using large-scale surveys, such as those used in this research, is that you can study everything you see in the resulting images, from asteroids near our solar system to the most distant galaxies in the early universe,” said Michael Strauss, a professor of astrophysical sciences at Princeton University who was not involved in the research, in a press release. You can use the same data to explore many new questions.”