The universe’s oldest and farthest ‘dark matter’ finally revealed by scientists

• Prior to this study, dark matter from 8-10 billion years ago had been studied.
• Data came from the Hyper Suprime Camera in Japan and ESA's Planck satellite.
• This is around the time galaxy clusters began to form.

A group of researchers from Japan and the U.S. has successfully managed to look at dark matter around galaxies from 12 billion years ago, the furthest so far, a press release said.

When scientists look at the data obtained from the telescopes such as the James Webb Space Telescope, they are looking at the past. Since light travels at a finite speed, what we see today are events that happened millions and even billions of years ago.

Measuring dark matter is even more difficult since it does not emit light. So, researchers put Einstein's theory of relativity to use and measured the distortion of light of faraway galaxies to determine the amount of dark matter of a galaxy in the foreground. The greater the bending of light, the greater the amount of dark matter in the 'lens' galaxy that is causing that distortion.

The problem with distant galaxies

As we look at galaxies that are further away, the light come from them becomes fainter, and the lensing due to a galaxy that one wants to study is so subtle that it is difficult to detect at all. Scientists have tried to use light signals from multiple galaxies to work around this problem, but the inability to detect many distant galaxies has meant that dark matter from only 8-10 billion years has been studied so far.

Since the universe began around 13.7 billion years ago, there is much unknown about the time it began and what happened soon after. To get a better understanding of this period of time, researchers at Nagoya University and Tokyo University in Japan, collaborated with the Japanese Astronomical Observatory and Princeton University in the U.S., to use a different source of background light, the microwaves from the Big Bang.

How researchers looked at the dark matter from 12 billion years ago

The collaboration looked at visible light data from the Subaru Hyper Suprime-Cam Survey (HSC) to identify 1.5 million lens galaxies from 12 billion years ago. They then used the cosmic microwave background (CMB) from the Big Bang to overcome the lack of light from galaxies that were even further away.

Using microwave data captured by the European Space Agency's Planck satellite, the researchers were able to measure the lensing of microwaves by these galaxies. "Most researchers use source galaxies to measure dark matter distribution from the present to eight billion years ago”, said Yuichi Harikane, Assistant Professor at the University of Tokyo, in the press release.

“However, we could look further back into the past because we used the more distant CMB to measure dark matter. For the first time, we were measuring dark matter from almost the earliest moments of the universe.”

Preliminary analysis showed that the researchers had sufficient data to determine the distribution of dark matter and were able to detect dark matter from 12 billion years ago. At 1.7 billion years from the Big Bang, these galaxies are still in their cosmic infancy. Around this time, the first galaxy clusters were also beginning to form. Galaxy clusters consist of 100 to 1000 galaxies that are bound by gravity and have large amounts of dark matter.

So far, the group has only analyzed a third of the data available from the HSC. Further analysis, will also include data from Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), allowing researchers to peer further back in time.

The findings were published in the journal Physical Review Letters.

Study Abstract:

We report the first detection of the dark matter distribution around Lyman break galaxies (LBGs) at high redshift through the cosmic microwave background (CMB) lensing measurements with the public Planck PR3 κ map. The LBG sample consists of 1 473 106 objects with the median redshift of z∼4 that are identified in a total area of 305 deg 2 observed by the Hyper Suprime-Cam Strategic Survey Program survey. After careful investigations of systematic uncertainties, such as contamination from foreground galaxies and cosmic infrared background, we obtain the significant detection of the CMB lensing signal at 5.1σ that is dominated by 2-halo term signals of the LBGs. Fitting a simple model consisting of the Navarro-Frenk-White profile and the linear-bias model, we obtain the typical halo mass of Mh=2.9^+9.5_−2.5×10¹¹h⁻¹M⊙. Combining the CMB lensing and galaxy-galaxy clustering signals on the large scales, we demonstrate the first cosmological analysis at z∼4 that constrains (Ωm0,σ8). We find that our constraint on σ8 is roughly consistent with the Planck cosmology, while this σ8 constraint is lower than the Planck cosmology over the 1σ level. This study opens up a new window for constraining cosmological parameters at high redshift by the combination of CMB and high-z galaxies, as well as studying the interplay between galaxy evolution and large-scale structure at such high redshift, by upcoming CMB and optical and near-infrared imaging surveys.