APR 13, 2018 12:00 PM PDT

Neutrinos, the "Hot" Dark Matter?

Cosmic structural formation under standard model vs BAHAMAS's model that includes neutrinos Credit: The Conversation/Ian G. McCarthy

When it comes to dark matter, the elusive existence that is supposed to make up 80% of all matter-energy in the universe, scientists have been scratching their heads to find out what it exactly is made of.

The BAHAMAS (BAryons and HAloes of MAssive Systems) group, a collective of astrophysicists and cosmologists, recently published their study based on the largest suite of cosmological computer simulations of normal and dark matter to date. According to their estimate, neutrinos can make up a small portion of the total dark matter mass.

There have been competing theories on the makeup of dark matter. The mainstream idea that most physicists follow is the standard cosmological model, in which dark matter is regarded “cold” because it is made of weakly interacting massive particles, or WIMPs. These WIMPs move sluggishly since the birth of the universe, and have been bonding with each other to form massive objects that are bound by gravity.

As the quantity and quality of cosmological observations improves over the recent years, scientists have been revamping their model based on the new observations using “gravitational lensing”, a phenomenon in which light from distant galaxies can be deflected by massive objects standing in its path. New data sets have led to a conclusion that the mass distribution in the universe appears to be less lumpy than predicted in the standard model, in which the dark matter is entirely cold.

Therefore, more and more astronomers and cosmologists start to postulate that the dark matter could, partly or wholly, be “warm” or even “hot”, meaning that the particles that make up dark matter could have medium to high velocities. A possible candidate of warm dark matter is the sterile neutrino: a heavier, slower form of neutrino, and the normal neutrino is a sound candidate for hot dark matter. The particles with high velocity could easily escape from matter-dense regions of the universe. This would slow the accumulation of new matter and lead to a universe where the formation of structure less lumpy, matching the recent observations.

The BAHAMAS project represents the first-ever attempt to survey large-scale structure (LSS) in the universe using self-consistent full cosmological hydrodynamical simulations, which simultaneously follows all of the important matter components and helps researchers address the main uncertainty in the theoretical modeling of LSS.

Based on careful comparisons, researchers concluded that the discrepancy between the new observational data sets and the standard cold dark matter model is even larger than previously claimed: by including neutrinos were included in the model, the structure formation in the cosmos was washed out, making the universe less lumpy. Their results suggest that neutrinos make up between 3% and 5% of the total dark matter mass.

Based their discovery, scientists at BAHAMAS also come up with a revised mass of a single neutrino. Previous studies have led physicists to conclude that the sum of the three neutrino species no less than 0.06 electron Volts (eV). By incorporating the newly estimated total neutrino contribution to dark matter, they deduced that the neutrino mass should be between 0.3 and 0.5 eV instead. The researchers hope that their estimated values can be verified in upcoming particle physics experiments.

What We (Don't) Know About Dark Matter. Credit: SciShow Space

Source: The Conversation

About the Author
  • With years of experience in biomedical R & D, Daniel is also very into writing. He is constantly fascinated by what's happening in the world of science. He hopes to capture the public's interest and promote scientific literacy with his trending news articles.
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