London | Scientists have proposed a new model for what the elusive dark matter might be and how the presence of this mysterious material can be tested. Dark matter is all around us.
Though no one has ever seen it, and no one knows what it really is, indisputable physical calculations state that approximately 27 per cent of the universe is dark matter, researchers said. Only five per cent is the matter of which all known materials consist, they said. Several types of devices have been put up on Earth and in space to capture the particles that dark matter is supposed to consist of, and experiments have attempted to create a dark matter particle by colliding ordinary matter particles at very high temperatures.
Even if such a collision succeeds, we would not be able to directly see the produced dark matter particle. It would immediately pass on and fly away from the detectors – but it will take some energy with it, and this energy loss will be recorded and indicate that a dark particle had been produced.
Despite all these initiatives no dark particle has yet been detected. Maybe dark matter is of a different character and needs to be looked for in a different way, said Martin Sloth, associate professor at the University of Southern Denmark. Dark matter is light and therefore interacts weakly with ordinary matter. This means that the particles are capable of being produced in colliders, researchers said.
This theory’s dark particles are called weakly-interacting massive particles (WIMPs), and are thought to have been created in an inconceivably large number shortly after the birth of the universe 13.7 billion years ago. But since no experiments have ever seen even a trace of a WIMP, it could be that we should look for a heavier dark particle that interacts only by gravity and thus would be impossible to detect directly, said Sloth.
Researchers call their version of such a heavy particle a PIDM particle (Planckian Interacting Dark Matter). In their new model, they calculated how the required number of PIDM particles could have been created in the early universe. It was possible, if it was extremely hot. To be more precise the temperatures in the early universe must have been the highest possible in the Big Bang theory, said Sloth.
If the universe indeed was as hot as calculated in our model, several gravitational waves from the very early childhood of the universe would have been created. We might be able to find out in the near future, he said. If these experiments do not detect such signals, then our model will be falsified. Thus gravitational waves can be used to test our model, he said. Dark matter is thought to be the gravitational glue that binds the galaxies together. No one knows what dark matter actually is.
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