Where did all the dwarf galaxies go?

Astronomers believe they’ve worked out why there are so many fewer dwarf galaxies than predicted: they’re moving so fast that their gas is simply whipped away.

High-precision observations show that our universe consists of about 75 percent dark energy, 20 percent dark matter and just five percent ordinary matter.

Simulations have shown that this situation should have led to the creation of a huge number of dwarf galaxies weighing just one thousandth of the Milky Way. However, only a handful have been found.

To help solve the mystery, researchers turned to the Constrained Local UniversE Simulations (CLUES) simulation, which uses the observed positions and velocities of galaxies within tens of millions of light years of the Milky Way to accurately simulate the local environment in ourt own galaxy.

“The main goal of this project is to simulate the evolution of the Local Group – the Andromeda and Milky Way galaxies and their low-mass neighbours – within their observed large scale environment,” says Stefan Gottlöber of the Leibniz Institute for Astrophysics Potsdam.

And what the team found is that some of the far-out dwarf galaxies in the Local Group move so fast with respect to the Cosmic Web that most of their gas can be stripped and effectively removed. They call this mechanism ‘Cosmic Web Stripping’, as it’s the pancake and filamentary structure of the cosmos that is responsible for depleting the dwarfs’ gas supply.

“These dwarfs move so fast that even the weakest membranes of the Cosmic Web can rip off their gas,” says Alejandro Benítez LLambay, PhD student at the Instituto de Astronomía Teórica y Experimental of the Universidad Nacional de Córdoba in Argentina.

Without a large gas reservoir out of which to form stars, these dwarf galaxies, he says, would be so small and dim that they’d hardly be visible today – meaning that they may simply be too faint to see.