The Milky Way galaxy mass is one of the most fundamental knowledge that astronomers can get about our galactic home. However, despite decades of intensive efforts, even the best available estimates of the mass of the Milky Way differ greatly. Now, by combining the new data from the ESA Gaia mission with observations made using the Hubble space telescope, astronomers have discovered that our Galaxy weighs about 1.5 trillion solar masses within a radius of 129,000 light-years from the center.
Previous estimates of the mass of the Milky Way ranged from 500 billion to 3 trillion solar masses. This huge uncertainty arose mainly due to various methods of measuring the distribution of dark matter, which is about 90% of the mass of the Galaxy.
We simply cannot observe dark matter directly, that is what leads to the current uncertainty in the mass of the Milky Way. You can’t measure exactly what you don’t see!
-the head of the analytical group Laura Watkins of the European Southern Observatory (Germany)
Given the elusive nature of dark matter, the team had to use a clever method to “weigh” the Milky Way, based on measuring the velocities of globular clusters – dense star groups that rotate around the spiral disk of the Galaxy.
The more massive the galaxy, the faster its clusters move under the influence of gravity. Most of the previous measurements focused on the speed at which the cluster approaches or moves away from the Earth, that is, moves along the line of sight. However, we were also able to measure the lateral movement of clusters, from which we can calculate the total velocity and, therefore, the galactic mass.
-N. Win Evans from the University of Cambridge (United Kingdom)
As a basis for the study, the group used the second data release of the “Gaia” mission, designed to create an accurate three-dimensional map of astronomical objects throughout the Milky Way and track their movements. The second data release includes measurements of globular clusters at a distance of 65,000 light years from Earth.
The team combined data on 34 globular clusters with the observational heritage of the Hubble space telescope, which added 12 dull and distant clusters to the study at a distance of up to 130,000 light years from Earth. As Hubble watched them for a decade, it became possible to track their speed accurately. As a result, the synergy of space telescopes made it possible to refine the estimate of the mass of our Galaxy, which amounted to 1.5 trillion solar masses.
Until now, ignorance of the exact mass of the Milky Way has been a problem for finding answers to many fundamental questions. The content of dark matter in galaxies and its distribution are inextricably linked with the formation and growth of structures in the Universe. Accurately determining the mass of the Milky Way gives astronomers a clearer understanding of what our galaxy is in a cosmological context.
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