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Matter attracts matter, a phenomenon we are all familiar with as gravity. As early as the 1930s, the renowned astronomer Fritz Zwicky found out that some kind of “dark matter” accounts for the bulk of matter in galaxy clusters. He had investigated the motion of individual galaxies in galaxy clusters and found that mass was obviously missing.
This effect can also be observed in spiral galaxies. The orbital velocity of stars orbiting far from the center of the galaxy is much higher than the visible mass of the stars suggests. The conclusion is that there should also be a non-luminous, dark matter that exerts gravity. According to modern ideas, dark matter surrounds galaxies like a spherical cloud. This also applies to our own galaxy, the Milky Way.
In the last decades, dark matter has been accepted as the only assumption able to provide a model consistently describing all existing observations; one notable such observation is the temperature fluctuation of the of the cosmic microwave background, the reverberation of the Big Bang.
Further evidence is provided by the gravitational lensing effect, due to which light curves around matter, the stronger the more matter there is, independent whether it is luminous or dark. Furthermore, the investigations of galaxy collisions are pointing towards the existence of dark matter. Even if all these observable phenomena are conclusive and plausible: We still do not know what dark matter is made of.
According to nearly all well motivated theories dark matter is naturally occurring with the following properties:
If such dark matter exists, it should be possible to observe it from Earth with the right measuring instruments.
As part of the CRESST experiment, scientists are searching for dark matter particles scattering off nuclei. COSINUS aims to test the controversial claim of another experiment of having observed a dark matter signal. The concepts and technologies for both experiments were (and still are) mainly developed at the Max Planck Institute for Physics.
Two other experiments with MPP participation focus on very different candidates. These candidates are predicted to exist independently from the dark matter problem, meaning these can solve other problems of the standard model of particle physics.
The MADMAX experiment will be searching for axion dark matter. Axions have been originally introduced to explain the so called CP problem in the strong interaction and could also solve the dark matter problem.
TRISTAN is a new detector in the KATRIN experiment that searches for sterile neutrinos in an existing neutrino experiment. This could also be the substance for dark matter.
These approaches were also initiated by scientists at the MPP and are now being implemented together with research partners.
© 2019 Max Planck Institute for Physics, Munich