Dark Side of the Galactic Centre

The heart of the Milky Way might be quite dark. A new paper published in Nature Physics indicates that the core of our galaxy might contain significant amounts of dark matter. An estimated 84% of the matter in our universe is supposed to be made up of dark matter, the nature of which remains a mystery. Researchers have long predicted that large amounts of dark matter are harbored in the galactic core, but have never had any observational proof of this. The new paper in Nature Physics provides the first evidence to support the theory.

Fabio Iocco, a researcher at the ICTP South American Institute for Fundamental Research (ICTP-SAIFR) in Sao Paulo, Brazil, who is the paper's lead author, says,"[The results are] a very clean, conclusive answer to the question [of dark matter presence in the galaxy core]," adding, "We like to believe that this is a first sizeable step into an era of precision for dark matter distribution determination."

Theories on galaxy structure formation and numerical simulations of galaxy formation had predicted the presence of dark matter in the core of the Milky Way, but direct observational proof was lacking. Iocco and his co-authors carried out a meticulous study and calculated at different radii the difference between the observed rotation curve of the Milky Way and the rotation curve expected from only visible matter. This difference, which is indicative of presence of dark matter in the region, was found to be statistically significant at 5-sigma, confirming the presence of dark matter.

Iocco says that the main challenges the team overcame in measuring the presence of dark matter inside the Milky Way were distinguishing between the gravitational effects of dark matter from those of stars and interstellar gases (which are abundant in the centre) and accurately determining the rotation curves, which becomes problematic because we are inside the galaxy and moving with it.

The paper is available for download on Nature Physics. More information (in Portuguese) is published on the ICTP-SAIFR webpage.

ICTP-SAIFR is ICTP's partner institute in Sao Paulo, Brazil. It functions in collaboration with Sao Paulo State University (UNESP) and the Sao Paulo Research Funding Agency (FAPESP).