Interactive dark matter could explain Milky Way’s missing satellite galaxies

Scientists at Durham University could have unearthed a way to explain why there are not more galaxies around the Milky Way

Two models of the dark matter distribution in the halo of a galaxy like the Milky Way, separated by the white line. The colours represent the density of dark matter, with red indicating high-density and blue indicating low-density. On the left is a simulation of how non-interacting cold dark matter produces an abundance of smaller satellite galaxies. On the right the simulation shows the situation when the interaction of dark matter with other particles reduces the number of satellite galaxies we expect to observe around the Milky Way
Two models of the dark matter distribution in the halo of a galaxy like the Milky Way, separated by the white line. The colours represent the density of dark matter, with red indicating high-density and blue indicating low-density.

Scientists at Durham University believe they have found a way to explain why there are not more galaxies forming around the Milky Way.

The scientists, working with the LAPTh College and University in France, believe ‘interactive dark matter’ could explain the Milky Way’s missing galaxies.

This has thrown doubt on the generally accepted theory of ‘cold dark matter’, a substance that scientists predict should allow for more galaxies to have formed around the Milky Way than can be seen through telescopes.

Now, scientists at the university think that clumps of dark matter that emerged from the early universe trapped the gas needed to form stars and galaxies.

Writing in the journal Monthly Notices of the Royal Astronomical Society (MNRAS), the scientists – including cosmologists and particle physicists at the Institute for Computational Cosmology (ICC) and the Institute for Particle Physics Phenomenology (IPPP), at Durham University – suggest that dark matter particles, as well as feeling the force of gravity, could have caused the dark matter to scatter.

That would have wiped out the structures that can trap gas, stopping more galaxies from forming around the Milky Way and reducing the number that should exist.

The simulated distribution of dark matter in a Milky Way-like galaxies for standard, non-interacting dark matter (top left), warm dark matter (top right) and the new dark matter model that interacts with the photon background (bottom). Smaller structures are erased up to the point where, in the most extreme model (bottom right), the galaxy is completely sterilized.
The simulated distribution of dark matter in a Milky Way-like galaxies for standard, non-interacting dark matter (top left), warm dark matter (top right) and the new dark matter model that interacts with the photon background (bottom). Smaller structures are erased up to the point where, in the most extreme model (bottom right), the galaxy is completely sterilized.
 

Co-author Professor Carlton Baugh, in the ICC at Durham University, said: “Astronomers have long since reached the conclusion that most of the matter in the Universe consists of elementary particles known as dark matter.

“This model can explain how most of the Universe looks, except in our own backyard where it fails miserably.

“The model predicts that there should be many more small satellite galaxies around our Milky Way than we can observe.

“However, by using computer simulations to allow the dark matter to become a little more interactive with the rest of the material in the Universe, such as photons, we can give our cosmic neighbourhood a makeover and we see a remarkable reduction in the number of galaxies around us than originally thought.”

The researchers, who used powerful computer simulations to reach their findings, say that they offer an alternative theory.

Lead author Dr Celine Boehm, in the IPPP at Durham University, said: “We don’t know how strong these interactions should be, so this is where our simulations come in.

 

“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.

“This is an example of how a cosmological measurement, in this case the number of galaxies orbiting the Milky Way, is affected by the microscopic scales of particle physics.”

The calculations were carried out using the COSMA supercomputer at Durham University, which is part of the UK-wide DiRAC super-computing framework.

The work was funded by the Science and Technology Facilities Council and the European Union.

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