08/04 18:50
The little we know about dark matter comes from calculations based on the glow of surrounding galaxies. However, the farther we looked, the fainter the starlight became, making it difficult to see the subtle effect of it.
A collaboration between astronomers from Japan and the United States has found a different way to illuminate the distant darkness, by studying the way mysterious lumps of dark matter distort the background glow of the universe.
Dark matter is called by its name, just because it does not emit any information that tells us anything about its nature. It is likely to be a particle-like mass with few properties, not unlike a neutrino. There is an external chance that it is a reflection of something we misunderstood about the formation of space and time.
In short, we still do not have a concrete theory as to where this phenomenon fits in with current physics. So getting an accurate measure of what the ancient super dark matter halos looked like will at least tell us whether they have changed over time.
We cannot estimate its total mass – invisible and incandescent – by measuring its faint light. But it is possible to use the way their collective mass distorts starlight passing through the space around them.
This lensing technology works well enough for large groups of galaxies seen 8 to 10 billion years in the past. The more we want to see, the less background stellar radiation we want to analyze for distortions.
According to Nagoya University astrophysicist Hironao Miyatake and colleagues, there is another light source we can use, called the cosmic microwave background (CMB).
Think of the CMB as the oldest image of a newborn universe. The emitted light echoed when the universe was about 300,000 years old, and is now penetrating space as weak radiation.
Scientists use subtle patterns in this buzzing background to test all kinds of hypotheses in the early critical stages of the universe’s evolution. Its use was to estimate the average mass of distant galaxies and the distribution of their surrounding dark matter halos first.
“It was a crazy idea,” says Masami Oshi, an astrophysicist from the University of Tokyo. “No one realized we could do it. But after I gave a talk about a large, distant galaxy sample, Hironao came to me and said it might be possible to look at dark matter around These galaxies using CMB”.
Hironau and colleagues focused on a special group of distant star-forming objects called Lyman-break galaxies.
Using a sample of nearly 1.5 million of these objects collected by the Hyper Suprime-Cam Subaru strategic reconnaissance programme, they analyzed microwave radiation patterns as seen by the European Space Agency’s Planck satellite.
The findings provided the researchers with a typical halo mass for galaxies close to 12 billion years in the past, an era somewhat different from the one we see closer to home today.
According to standard cosmological theory, the composition of these early galaxies was largely determined by fluctuations in space that amplify the clump of matter. Interestingly, these new discoveries of early galactic masses reflect less clumping of matter than current preferred models predict.
Rethinking current models of how fresh elements came together to form the first galaxies could reveal gaps that may also explain the origins of dark matter.
This research was published in the journal Physical Review Letters.