See tiny clumps of dark matter in the virtual universe

Cosmologists have zoomed in on tiny clumps of dark matter in a virtual universe that could help them find it in real space. An international team of researchers has used supercomputers in Europe and China to focus on a typical region of the computer universe. The magnification they were able to achieve is equivalent to being able to see a flea on the lunar surface. This allowed them to take detailed images and analyze hundreds of virtual dark matter clumps (or halos) from the largest to the smallest. Particles of dark matter can collide with antiparticles of dark matter near the center of the halo, where, according to some theories, they turn into a burst of energetic gamma rays. The scientists’ findings, published in the journal Nature, could mean that these very small halos could be identified in future observations from the radiation they are believed to emit.

Study co-author Carlos Frank, professor of fundamental physics at Ogden at the Institute for Computational Cosmology at the University of Durham, UK, said: “By zooming in on these relatively tiny dark matter halos, we can calculate the amount of radiation that is expected from different sources. Much of this radiation will be emitted by halos of dark matter too small to contain stars, and future gamma-ray observatories could detect these emissions, making these small objects individually or collectively “visible”. This will confirm the hypothesis about the nature of dark matter, which may not be entirely dark”.

Most of the matter in the Universe is dark (with the exception of gamma radiation, which they emit in exceptional circumstances) and completely different in nature from the matter of which stars, planets, and even humans are made.

The universe is roughly 27% dark matter, with the rest composed mostly of equally mysterious dark energy. Ordinary matter such as planets and stars make up a relatively small 5% of the universe.

Galaxies formed and grew as gas-cooled and condensed in the center of huge clumps of this dark matter – the so-called dark matter halos. Astronomers can infer the structure of large dark matter halos from the properties of galaxies and the gas inside them.

The largest halos contain huge clusters of hundreds of bright galaxies that weigh 1,000 trillion times more than our Sun. However, scientists have no direct information on smaller dark matter halos, which are too small to contain the galaxy. They can only be studied by simulating the evolution of the universe on a large supercomputer.

The smallest are believed to have the same mass as Earth, according to current popular science theories about dark matter, which are at the heart of the new study.

The simulations were carried out using the Cosmology Machine, part of the DiRAC high-performance computing system in Durham, funded by the Science and Technology Council (STFC), and computers from the Chinese Academy of Sciences.

By enlarging the virtual universe with such microscopic details, the researchers were able to study the structure of dark matter halos, the mass of which ranges from Earth to a large cluster of galaxies.

Surprisingly, they found that halos of all sizes have a very similar internal structure and are extremely dense in the center, becoming more common, with smaller clumps orbiting in the outer regions. The researchers said that without a measurement scale, it was nearly impossible to distinguish an image of a dark matter halo in a massive galaxy from a halo with a mass that is a fraction of the sun.

We expect that there will be an extremely large number of small dark matter halos, they will contain a significant part of all dark matter in the Universe, but mostly they will remain dark throughout the entire cosmic history because stars and galaxies grow only in halos that are more than a million times more massive than the sun.

Professor Simon White of the Max Planck Institute for Astrophysics, Germany

“Our research sheds light on these little halos as we seek to learn more about what dark matter is and what role it plays in the evolution of the universe,” the scientists conclude.

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