Dark Matter is the hypothetical substance that permeates and binds galaxies together. Evidence for its existence is found in the motion of galaxies and clusters of galaxies, and researchers believe that vast haloes of dark matter surround these cosmic objects. A study published in Nature today argues that these haloes are structurally all the same, no matter what size.

The simulation indicates that it doesn’t matter how big or how small your dark matter halo is, the distribution of dark matter will always look the same. It will be much denser in the middle (without clumping up) and more diffuse at the edges, with smaller clumps orbiting the larger ones.

Although galaxies only form in haloes that are at least a million times more massive than the Sun, the team wanted to investigate the broadest possibilities that simulations allowed them. Across 20 orders of magnitude they witnessed this remarkable similarity in haloes 1,000 trillion times the mass of the Sun all the way down to haloes one-third the weight of Earth.  

"We were really surprised by our results," co-author Simon White from the Max Planck Institue for Astrophysics, said in a statement. "Everyone had guessed that the smallest clumps of dark matter would look quite different from the big ones we are more familiar with. But when we were finally able to calculate their properties, they looked just the same."

The “zoom” simulation was developed by researchers in China, Germany, the UK, and the USA, over the course of five years. The properties of the larger dark matter haloes were worked out by comparing the simulated universe to what astronomers observe in the real universe.

Dark matter is assumed to be made by weakly interacting massive particles, or WIMPs. These don’t emit or absorb any light and are expected to be roughly 100 times the mass of a proton, the particle that sits in the nucleus of an atom.

An interesting consequence of the study is the supposed gamma-rays emission that the annihilation of dark matter produces. According to the simulations, this is a thousand times smaller than what was previously expected.

A recent study on gamma-ray excess from the center of the Milky Way excluded dark matter as a source, so it would be interesting to see if a weaker signal from dark matter would fit the observations.