The universe is slightly hotter than it should be, 'Dark photons' could be to blame

These strange particles would be the carriers of a new, fifth force of nature that normal matter does not experience, but occasionally these dark photons can flip their identities to become regular photons, providing a source of heat.

We could find such dark photons by observing the intergalactic gas using what's known as the Lyman-alpha forest. When we observe light from a distant, bright object, like a quasar (glowing objects powered by black holes at the centers of distant galaxies), there is a series of gaps in an otherwise smooth spectrum of light from that faraway object. 

Here's why: that light has to filter through billions of light-years of gas to reach us. Occasionally that light will pass through a relatively dense clump of neutral hydrogen — a type of hydrogen that consists of one proton and one neutron, and which permeates gas clouds throughout the universe. 

Most of that light will pass through unaffected, but a very specific wavelength of light will get absorbed. This wavelength corresponds to the energy difference needed to bump an electron from its first to its second energy level inside the hydrogen atoms.

This is a very hypothetical form of dark matter, the mysterious, invisible substance that accounts for roughly 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 as to what it could be.

In this model, instead of the dark matter being made of invisible particles (like a phantom version of electrons, for example), it would instead be made of a new kind of force carrier — that is, a type of particle that mediates interactions between other particles.

Source Ref: LiveScience