Dark matter comprises 85% of matter in the universe. Until now, all the efforts for the detection of dark matter on Earth remain unsuccessful. As dark matter doesn’t interact with light, it is not possible to see it. The biggest challenge for astronomers, who study dark matter, is how to learn the invisible thing. The detection of dark matter is possible through its gravitational influence on light and other matter.
Facts about Dark Matter
Despite its mysterious nature, astronomers found out that Dark Matter is not only dark but also cold. It forms the seeds of galaxy clusters. Dark matter also forms haloes around galaxies. The majority of the mass of galaxies is due to this. The astronomers often develop new models for dark matter, comparing them to observation to test their accuracy to solve the unanswered questions.
Computer Simulation Study
Simulations on computers are the way to develop a new model and compare it with observation. A team of astronomers at the Harvard & Smithsonian Center for Astrophysics carried out detailed simulations on dark matter cosmos. The outputs from these simulations are exciting and surprising as well.
Assumptions in simulating the dark matter plays a vital role. These assumptions will decide about the accuracy of the simulation results—weakly interacting massive particles (W.I.M.P), which is one of the famous theories for Dark Matter. The research team assumed that W.I.M.P with a mass about 100 times that of a proton, made up the dark matter. In the past, W.I.M.P dark matter study was not new, but this latest study was exceptionally high in resolution, simulating features on a scale ranging across thirty orders of magnitude. This study hints at how dark matter would look like if we can see it.
Dark Matter, in this simulation, formed in haloes around galaxies, just as we observe. But interestingly, it found that haloes also developed at all mass scales, from small, planet-mass haloes, to galactic haloes, to massive haloes that form around clusters of galaxies. These haloes have a similar structure, where they are most dense toward their center, becoming more diffuse at their edges. The fact that this happens at all scales makes it an explicit feature of dark matter. The simulation results in haloes of all scales and possibly hinting about how dark matter would look.
Small Scale Haloes
While the small scale haloes are too small to be detected through their gravitational influence on light, they could tell us about how dark matter interacts with itself. One idea about Dark Matter is that when dark matter particles collide, they emit gamma radiation. Some gamma-ray observations have hinted at a gamma-ray excess coming from the center of our galaxy, which could be caused by Dark Matter. In this particular model, most gamma radiation produced by dark matter would come from smaller haloes. Since the scale of a halo would affect the energy spectrum of the gamma rays, this model makes specific predictions about the gamma-ray excess we should see both in the Milky Way and other galaxies.
The reference for this study is as follows:
- Wang, J., Bose, S., Frenk, C.S. et al. “Universal structure of dark matter haloes over a mass range of 20 orders of magnitude.” Nature 585.7823 (2020): 39-42.