The recent findings show that the intergalactic gas in our universe is slightly hotter than expected. To explain this, a group of astrophysicists has developed a novel idea through computer simulations. They propose that the cause could be "dark photons," an uncommon type of dark matter that brings a new fifth force to nature. Unlike normal matter, this force is not experienced by normal matter. These dark photons can transform into regular photons and supply heat to the universe.
It appears that the intergalactic gas in our universe is slightly warmer than anticipated. Astrophysicists used advanced computer simulations to find an explanation and devised a unique idea. They think "dark photons," a type of unusual dark matter, could be responsible for the elevated temperature. These dark photons act as carriers of a new fifth force of nature, which regular matter doesn't experience. However, at times, these dark photons change into regular photons, contributing to the heat in the universe.
SciTechDaily explained the reason for this is that the light from distant stars has to travel billions of light-years through gas before reaching us. During its journey, the light may encounter clumps of neutral hydrogen, which makes up gas clouds in the universe. Most light will pass through these clumps unscathed, but a particular wavelength of light will be absorbed. This wavelength matches the energy required to boost an electron from its first to its second energy level within hydrogen atoms.
Studying the 'Light'
When astronomers study the light emitted by a celestial object, it appears normal except for a missing section at the specific energy transition wavelength referred to as the Lyman-alpha line.
As the light passes through various clouds and clumps of neutral hydrogen, it experiences multiple gaps. The universe's expansion causes these gaps to redshift to different wavelengths, with a new gap appearing at a different wavelength based on the distance to a specific cloud of gas. This process creates the "forest" - a series of lines and gaps in the spectrum.
According to Live Science, the Lyman-alpha gaps can also be utilized to determine the temperature of gas clouds. In an ideal scenario where the neutral hydrogen is at rest, the gap would appear as a very thin line. But if the individual molecules are in motion, the gap will widen due to their kinetic energy. The higher the temperature of the gas, the greater the kinetic energy of the molecules, resulting in a wider gap.
A group of astrophysicists published a paper in the Physical Review Letters in November, highlighting that through this method, the gas clouds between galaxies seem to be slightly too warm. Computer simulations of the gas clouds' evolution predict them to be slightly cooler than what was observed. Hence, there might be an unknown factor heating these clouds that is not accounted for in current astrophysical simulations.
A galaxy with a large reservoir of dark matter (purple overlay) in its center.
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Hypothetical Form of Dark Matter
One proposed explanation for the discrepancy is the existence of "dark photons," as per the authors of the study. Dark photons are a hypothetical form of dark matter - the mysterious and invisible substance that doesn't interact with light, accounting for 80% of all mass in the universe.
As astronomers have yet to determine the identity of dark matter, the possibilities are endless. In this model, instead of being composed of invisible particles (e.g., a phantom version of electrons), dark matter would be made of a new force carrier particle, mediating interactions between other particles.
The photon is the force carrier of electromagnetism and is responsible for electricity, magnetism, and light. Dark photons would be the force carrier of a new, fifth force of nature that doesn't occur in normal scenarios, such as in our labs or the solar system.
The study authors propose that the dark photons, while having some mass, can still contribute to the dark matter. As force carriers, they may also interact with other dark matter particles and with themselves. In the simulations conducted by astrophysicists, dark photons can convert into regular photons.
The team's findings are based on computer simulations incorporating dark photons into the universe's evolution. The results suggest that the presence of dark photons could explain the observed discrepancy between the temperature of the intergalactic gas and the temperature predicted by astrophysical simulations. However, other explanations for the discrepancy, such as inaccurate observations or poor understanding of normal astrophysical heating between galaxies, are still possible. Further research and observations are needed to explore the viability of dark photons as a possible explanation for the observations.
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