Max Planck Institute for Astrophysics | 2020 Sep 02
Most of the matter in the Universe is dark and thus not directly observable. In results just published in the journal Nature, an international research team harnessed supercomputers in China and Europe to zoom into a typical region of a virtual universe by a totally unprecedented factor, equivalent to that needed to recognise a flea on the surface of the full Moon. This allowed the team to make detailed pictures of hundreds of virtual dark matter haloes from the very largest to the very smallest expected in our Universe.This image shows a slice through the main simulation which is more than two billion
light years on a side. The two insets are successive zooms into regions which are 700
thousand and then just 600 light-years on a side. The largest individual lumps in the
main image correspond to clusters of galaxies, while the smallest lumps in the second
zoom are similar in mass to the Earth. Credit: MPA, Sownak Bose (CfA)
Dark matter plays an important role in cosmic evolution. Galaxies grew as gas cooled and condensed at the centre of enormous clumps of dark matter, so-called dark matter haloes. The haloes themselves separated from the overall expansion of the universe as a result of the gravitational pull of their own dark matter. Astronomers can infer the structure of big dark matter haloes from the properties of the galaxies and gas within them, but they have no information about haloes that might be too small to contain a galaxy.
The biggest dark matter haloes in today's universe contain huge galaxy clusters, collections of hundreds of bright galaxies. Their properties are well studied, and they weigh over a quadrillion (1015) times as much as our Sun. On the other hand, the masses of the smallest dark matter haloes are unknown. The theory of dark matter that underlies the new supercomputer zoom suggests that they may be similar in mass to the Earth. Such small haloes would be extremely numerous, containing a substantial fraction of all the dark matter in the universe, but they would remain dark throughout cosmic history because stars and galaxies grow only in haloes at least a million times more massive than the Sun. ...
The result has a potential practical application. Particles of dark matter can collide near the centres of haloes, and may - according to some theories - annihilate in a burst of energetic (gamma) radiation. The new zoom simulation allows the scientists to calculate the expected amount of radiation for haloes of differing mass. Much of this radiation could come from dark matter haloes too small to contain stars. Future gamma-ray observatories might be able to detect this emission, making the small objects individually or collectively "visible". This would confirm the hypothesised nature of the dark matter, which may not be entirely dark after all!
Zooming In on Dark Matter
Durham University, UK | 2020 Sep 02
Universal Structure of Dark Matter Haloes over a Mass Range of 20 Orders of Magnitude ~ Jie Wang et al
- Nature 585(7823):39 (03 Sep 2020) DOI: 10.1038/s41586-020-2642-9
- arXiv.org > astro-ph > arXiv:1911.09720 > 21 Nov 2019