New Study Finds No Evidence for Dark Matter in the Milky Way
A team using the MPG/ESO 2.2-meter telescope at ESO’s La Silla Observatory, along with other telescopes, has mapped the motions of more than 400 stars up to 13,000 light-years from the Sun. From this new data they have calculated the mass of material in the vicinity of the Sun, in a volume four times larger than ever considered before.
“The amount of mass that we derive matches very well with what we see -- stars, dust and gas -- in the region around the Sun,” says team leader Christian Moni Bidin (Departamento de Astronomia, Universidad de Concepcion, Chile). “But this leaves no room for the extra material -- dark matter -- that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there!”
Dark matter is a mysterious substance that cannot be seen, but shows itself by its gravitational attraction for the material around it. This extra ingredient in the cosmos was originally suggested to explain why the outer parts of galaxies, including our own Milky Way, rotated so quickly, but dark matter now also forms an essential component of theories of how galaxies formed and evolved.
Today it is widely accepted that this dark component constitutes about the 80% of the mass in the universe, despite the fact that it has resisted all attempts to clarify its nature, which remains obscure. All attempts so far to detect dark matter in laboratories on Earth have failed.
Astronomers’ existing models of how galaxies form and rotate suggest that the Milky Way is surrounded by a halo of dark matter. They are not able to precisely predict what shape this halo takes, but they do expect to find significant amounts in the region around the Sun. But only very unlikely shapes for the dark matter halo -- such as a highly elongated form -- can explain the lack of dark matter uncovered in the new study.
The new results also mean that attempts to detect dark matter on Earth by trying to spot the rare interactions between dark matter particles and “normal” matter are unlikely to be successful. They also improve our basic understanding of the space environment around Earth. This information could help scientists understand the conditions that have allowed Earth to become habitable for life as we know it - and the liklihood of finding similarly habitable planets in the Universe.
“Despite the new results, the Milky Way certainly rotates much faster than the visible matter alone can account for. So, if dark matter is not present where we expected it, a new solution for the missing mass problem must be found. Our results contradict the currently accepted models. The mystery of dark matter has just become even more mysterious. Future surveys, such as the ESA Gaia mission, will be crucial to move beyond this point.” concludes Christian Moni Bidin.