The new simulation shows exactly what dark matter looks like if we can see it

The new simulation shows exactly what dark matter looks like if we can see it

How do you study the invisible? This is a challenge faced by astronomers studying dark matter. Dark matter makes up 85% of all matter in the universe, but does not interact with light. It can only be seen through gravitational effects on light and other matter. To make matters worse, efforts so far to directly detect dark matter on Earth have failed.

Despite the difficult properties of dark matter, we have learned a few things about it. We know it’s not only dark, it’s cold. As a result, they clump together to form the seeds of the cluster. It also often forms a halo around the galaxy, making up most of the galaxy’s mass. However, there are still many unanswered questions about dark matter, so astronomers often develop new models for dark matter, comparing them with observations to test their accuracy.

One way to do this is to use sophisticated computer simulations. Recently, a team at the Harvard & Smithsonian Center for Astrophysics ran a detailed simulation of the dark matter universe, with amazing results.

An IceCube neutrino detector in Antarctica has detected WIMP. Credit: IceCube Collaboration/NSF

The accuracy of a dark matter simulation depends on your assumptions about dark matter. In this case, the team Weakly interacting large particles (WIMP) It is about 100 times the mass of a proton. WIMP is one of the most popular theories about dark matter. Similar computer simulations of WIMP dark matter have been performed previously. Nevertheless, this was very high resolution and simulated the function on a scale of up to 30 digits.

As we observed in this simulation, dark matter formed in the halo around the galaxy. Interestingly, however, we found that halos developed at all mass scales, from halos of small planetary masses to halos of galaxies to massive halos that form around clusters of galaxies. These halos have a similar structure, they are densest towards the center and more diffuse at the edges. The fact that this happens on all scales makes dark matter an obvious feature.

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The simulation shows a dark matter halo on all scales. Credit: J. Wang; S. Bose / Center for Astrophysics

The small scale halo is too small to detect through the effect of gravity on light, but it can tell you how dark matter interacts. One idea for dark matter is that dark matter particles emit gamma radiation when they collide. Some gamma ray observations The excess of gamma rays from the center of our galaxy can be caused by dark matter. In this particular model, most of the gamma rays produced by dark matter come from smaller halos. Because the size of the halo affects the energy spectrum of the gamma ray, this model makes specific predictions about the gamma ray excess we see in the Milky Way and other galaxies.

Dark matter is one of the biggest unsolved problems in modern astronomy. We’d love to detect it ourselves, but until that happens, simulations like this are one of the most powerful tools to better understand dark matter.

Reference: Wang, J., Bose, S., Frenk, CS et al. “Universal structure of a dark matter halo over a 20-digit mass range.” nature 585.7823 (2020): 39-42.

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