Observations indicate that the intergalactic gas in our universe is slightly hotter than it should be. Recently, a team of astrophysicists used sophisticated computer simulations to propose a radical solution: an exotic form of dark matter known as “dark matter”. photons“It could be heating up the place.
These strange particles will be carriers of a new, fifth force of nature that ordinary matter does not experience, but sometimes these dark photons can flip their identities to become regular photons, providing a source of heat.
We can find such dark photons by observing the intergalactic gas using what is known as the Lyman Alpha Forest. When we observe light from a distant, bright object, such as a quasar (glowing objects powered by black holes In the centers of distant galaxies), there are a series of gaps in the smooth spectrum of light from this distant object.
Here’s why: This light has to travel through billions of light-years of gas to reach us. Occasionally, that light passes through a relatively dense mass of neutral hydrogen — a type of hydrogen consisting of one proton and one neutron, which permeates clouds of gas throughout the universe.
Most of this light will pass unaffected, but a A very specific wavelength of light will suck. This wavelength corresponds to the energy difference needed to propel an electron from its first energy level to its second energy level within the hydrogen atoms.
When astronomers look at the light from this object, it will appear otherwise unremarkable except for a gap in the wavelength of a specific energy transition, known as the Lyman-alpha line.
The light from the distant object will pass through several clouds and masses of neutral hydrogen. The expansion of the universe redshifts the gaps to different wavelengths, with a new gap appearing at a different wavelength depending on the distance to the particular gas cloud.. The end result of this is the “forest”: a series of lines and gaps in the spectrum.
Get hot here
These Lyman-alpha gaps can also be used to measure the temperature of each gas cloud. If neutral hydrogen were completely stable, the gap would appear as an incredibly thin line. But if individual particles are moving, the gap will widen due to the kinetic energy of those particles. The hotter the gas, the greater the kinetic energy of the molecules, and the wider the gap.
In a paper published in November in the journal Physical review letters, a team of astrophysicists pointed out that using this method, the clouds of intergalactic gases appear to be very hot. Computer simulations of the evolution of those gas clouds predict that they are a little cooler than what we observe, and so maybe something is heating up those clouds that are not currently accounted for in astrophysical simulations.
The study authors claim that one possible explanation for this discrepancy is the existence of “dark photons” in our universe. This is a very default form of dark matterthe mysterious, invisible matter that accounts for nearly 80% of all the mass in the universe, yet doesn’t seem to interact with light.
Since astronomers do not currently understand the identity of dark matter, the field is wide open with possibilities for what it could be. In this model, instead of dark matter being made of invisible particles (like a ghostly version of electrons, for example), it would instead be made of a new type of force carrier—that is, a type of particle that mediates interactions between other particles.
Warm and fuzzy darkness
The familiar photon is the force carrier of electromagnetism – it is what generates electricity, magnetism and light. Dark photons will be force carriers for a new force of nature that does not operate at usual scales in usual scenarios (for example, in our laboratories or inside Solar Systemwhich we have already noticed).
According to the study’s authors, dark photons would still have a very small mass, and so they could still explain dark matter. In addition, since they are force carriers, they may also interact with each other and with other possible dark matter particles. In the models researched by the team of astrophysicists, dark photons can do another trick: they can sometimes transform into an ordinary photon.
In physical terms, dark photons can “mix” with normal photons, and they rarely exchange identities. When they do, the newly created photon continues to do what regular photons have always done: heat things up. Researchers have performed the first-ever simulation of the evolution of the universe, including the effects of these shape-shifting dark photons. They found that a particular combination of the dark photon’s mass and the probability of becoming a regular photon could explain the heating paradox.
This result is very far from the case for dark photons. A range of possibilities could also explain the Lyman-alpha results, such as inaccurate observations or a poor understanding of (normal) astrophysical heating between galaxies. But it is an interesting piece of evidence, and the findings can be used as a starting point for further exploration of the feasibility of this bizarre idea.