Dark Matter Scatters Before the Light

Durham University. A simulation of dark matter distribution, red most intense. Left hand side represents traditional models, on the right is what would occur if light can weakly scatter dark matter.

If Darth Vader had studied galactic evolution, he might never have thought the power of the dark could withstand light’s force. A new explanation for puzzling astronomical observations relies on the force provided by photons of light having scattered dark matter during the formation of the Milky Way.

Recently, astronomers have become bothered by the small satellite galaxies around our own. For one, there are fewer of them than our models of galaxy formation suggest. For another, their locations and movements don’t seem to be random, as these same models predict.

In The Monthly Notices of the Royal Astronomical Society, a team led by Dr. Celine Boehm of Durham University note that these models of satellite galaxy formation rely on dark matter to provide a gravitational seed attracting the gas which eventually become stars. These models depend on dark matter’s gravity affecting the more familiar particles, but exclude or ignore other sorts of interactions.

Since we still don’t really know what dark matter is, this is not surprising. We're not sure whether it interacts with the visible universe in any other way, but we are confident that if such interactions exist at all they aren't strong; thus why they're considered Weakly Interacting Massive Particles (WIMPs).

However, Boehm tried modeling what would happen if neutrinos and photons of light apply a force to dark matter, causing the dark matter particles to scatter. The result is fewer spots of matter clumped enough to start attracting gas. “By tuning the strength of the scattering of particles, we change the number of small galaxies, which lets us learn more about the physics of dark matter and how it might interact with other particles in the universe,” Boehm says.

Co-author Dr. Carlton Baugh, also from Durham University, says our cosmological model, “can explain how most of the universe looks, except in our own backyard where it fails miserably."

However, with the models including just a small amount of interaction between dark and ordinary matter Baugh says, “We can give our cosmic neighbourhood a makeover and we see a remarkable reduction in the number of galaxies around us compared with what we originally thought." With dark matter thought to outweigh the particles we can see by a factor of more than five, understanding it better is hugely important to knowing how the universe works.

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