For the first time, scientists have shown the presence of dark matter in the innermost part our galaxy, the Milky Way. While the mystery remains as to what dark matter actually is, the new results will help scientists search for dark matter particles and better understand the structure and evolution of our galaxy.
A central tenet in modern cosmology and astrophysics is the presence of a mysterious form of matter – dubbed dark matter – which is about five times more abundant than the ordinary matter, made of atoms, that we are familiar with.
Back in the 1970s, scientists firmly established the existence of dark matter using a range of techniques, including measurement of the rotation speed of gas and stars, which is a way of effectively ‘weighing’ the host galaxy and determining its total mass. These measurements showed that visible matter only accounts for a fraction of the total weight of a galaxy – its predominant part comes from dark matter.
Scientists have applied this technique to our own galaxy, and have previously ascertained the existence of dark matter in the outer parts of the Milky Way. But until now, it has proven very difficult to measure the rotation of gas and stars in the innermost part of the galaxy with the precision needed to pin down the presence of dark matter.
Dark matter in our cosmic neighbourhood
As reported in the journal Nature Physics, scientists from the Technische Universität München (TUM), Stockholm University, Universidad Autónoma de Madrid, ICTP South American Institute for Fundamental Research, and University of Amsterdam have now obtained the first observational proof of the presence of dark matter in the innermost part of the Milky Way – including our own ‘cosmic neighbourhood’.
This is the part that includes Earth and our Solar System, which is about 26,000 light years away from the centre of the galaxy. The diameter of our galaxy is about 100,000 light years.
First, the researchers created the most complete compilation to date of published measurements of the motion of gas and stars in the Milky Way. Then they compared the measured rotation speed with that expected under the assumption that only luminous matter exists in the Galaxy. The comparison clearly showed that the observed rotation cannot be explained unless large amounts of dark matter exist around us, and between us and the galactic centre.
“One of the most important science questions of our times” still unanswered
“We know that dark matter is needed in our Galaxy to keep the stars and gas rotating at their observed speeds,” says Miguel Pato, who conducted the analysis at TUM. “However, we still don’t know what dark matter is composed of. This is one of the most important science questions of our times.”
The results open up a new avenue for determining the distribution of dark matter inside the galaxy. With future astronomical observations, the method will enable scientists to measure the distribution of dark matter in our galaxy with unprecedented precision.
“This will permit [us] to refine the understanding of the structure and evolution of our galaxy. And it will trigger more robust predictions for the many experiments worldwide that search for dark matter particles,” says Pato.
Adapted from article by Andreas Battenberg, TUM Research News