An article published in the journal “Nature Astronomy” reports the reconstruction of the 3D movements of 10 stars in the Sculptor Dwarf Galaxy selected within a larger sample of over 100 among those with the smallest measurement errors. A team of researchers used observations made using the Hubble Space Telescope in 2002 and subsequent observations carried out by ESA’s Gaia space probe between 2014 and 2015 to produce this reconstruction that confirms the “cold” dark matter model.
The Sculptor Dwarf Galaxy is a small Milky Way satellite galaxy about 290,000 light years from it. It’s a spheroidal dwarf galaxy, a category of very small and very faint galaxies, the reason why they were discovered only recently and are mainly satellite galaxies of the Milky Way and Andromeda. Due to its cataloging, it’s also called the Sculptor Dwarf Spheroidal Galaxy.
The observations made by space and ground-based telescopes can be useful even a long time later, in this case 11 observations of a region of the Sculptor Dwarf Galaxy carried out with the Hubble Space Telescope in 2002 with the result of framing hundreds of stars. The Gaia space probe is also a space telescope launched in December 2013 that performs a constant monitoring of the sky so it repeatedly observed that dwarf galaxy.
A team of astronomers from various Dutch institutions used those data to select the 126 stars in the observations of both telescopes and to check which of them had positions accurate enough to be able to reconstruct their 3D motion. Eventually, 10 stars met those requirements and it was possible to study through their motion the gravitational effects they were subjected to, including those by dark matter.
This type of research was carried out because the Sculptor Dwarf Galaxy is a type of galaxy considered to be one of the most dominated by dark matter and is therefore an ideal object to investigate the characteristics of this type of matter of which very little is known yet. Among scientists there are those who are not convinced that dark matter exists, so research into the gravitational effects that led to the theory of its existence is important to test the models about it but also alternative models.
The model that is most widely accepted is that of cold dark matter. It describes the formation and evolution of structures in the universe and the formation of galaxies within dark matter halos with a particular shape. Measuring the motion of stars within a galaxy dominated by dark matter can help test that model by providing information on the dark matter halos in which that galaxy is immersed.
This study also indicated how the Sculptor Dwarf Galaxy is orbiting the Milky Way in an elongated orbit. However, the main result is certainly tied to the study of dark matter. According to Davide Massari of the University of Groningen, in the Netherlands, the lead author of the article, the type of movement measured can’t be predicted by alternative dark matter models or by models that exclude its existence.