Dark matter ‘observed’ in the inner part of our Milky Way
New research shows the presence of dark matter in the innermost part of the Milky Way, including in our Solar System and in the neighbourhood of planet Earth. The implications of the study published yesterday in Nature Physics are remarkable: dark matter does exist around us and also between us and the centre of our galaxy. This research also constitutes an important step in the direction of grasping the nature of dark matter.
Despite being undetectable by standard telescopes, dark matter is believed to account for most of the matter (26.8% against the 4.9% of ordinary matter, while dark energy accounts for the remaining 68.3%) in the Universe. Its presence and properties are inferred from its gravitational effects on visible matter, radiation and all the other large-scale structure of the observable Universe. Dark matter was postulated by Jan Oort in 1932 – though on the basis of inadequate evidence – and by Fritz Zwicky in 1933 to account for evidence of “missing mass” in the orbital velocities of galaxies in clusters. More adequate evidence was given in 1939 by Horace W. Babcock, but was only in the 1960s-1970s that Vera Rubin offered robust evidence supporting the existence of dark matter.
The existence of dark matter in the outer parts of the Milky Way is well established, but it has always proven very difficult to reveal its presence in the innermost regions of our galaxy, where our Solar System is located. This is due to the difficulty of measuring the rotation of gas and stars – which is used to infer about the existence of dark matter – with enough precision, from our position in the Milky Way. “In our new study, we obtained for the first time a direct observational proof of the presence of dark matter in the innermost part of the Milky Way. We have created the most complete compilation so far of published measurements of the motion of gas and stars in the Milky Way, and compared the measured rotation speed with that expected under the assumption that only luminous matter exists in the Galaxy. The observed rotation cannot be explained unless large amounts of dark matter exist around us, and between us and the Galactic centre” – says Miguel Pato at the Department of Physics, Stockholm University.
The research has even deeper implications. “Our method will allow for upcoming astronomical observations to measure the distribution of dark matter in our Galaxy with unprecedented precision. This will permit to refine our 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. The study therefore constitutes a fundamental step forward in the quest for the nature of dark matter” – concluded Pato.
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