Astronomers from NASA and the European Space Agency (ESA) have been able to determine that the Milky Way weighs about 1.5 Trillion solar masses and has a radius of 129,000 light years from the galactic center.
The recently obtained numbers are far more concrete than those that until now were handled.
Previously, astronomers believed that the Milky Way’s weight ranged between 500 billion to 3 trillion Solar Masses. In 2016, measurements revealed a more accurate number suggesting the Milky Way’s weigh was just around 700 Billion Solar Masses.
But even that was far from accurate it turns out.
“We simply cannot observe dark matter directly,” Laura Watkins, of the European Southern Observatory in Germany, said in a statement.
“That is what leads to uncertainty regarding the mass of the Milky Way: you cannot accurately measure what you cannot see,” adds the astronomer, who led the new study.
But just because you can’t weigh dark matter doesn’t necessarily mean there are no other ways to find the weight of our galaxy.
Watkins and her colleagues resorted to another method, consisting in measuring the speed of the so-called globular clusters: dense accumulations of stars orbiting the center of the galaxy.
According to N. Wyn Evans of the University of Cambridge, “the more massive a galaxy is, the faster its clusters move under the force of its gravity.”
“Most previous measurements revealed the speed at which a cluster is approaching or receding from Earth, that is the velocity along our line of sight. However, we were able to measure the sideways motion of the clusters, from which the total velocity, and consequently the galactic mass, can be calculated.”
The astronomers used data from ESA’s Gaia mission to measure globular clusters in a radius of 65,000 light-years from Earth, as well as data from Hubble, NASA, and ESA, to measure clusters in a radius of up to 130,000 light-years from our planet.
Astronomers used data gathered by the Gaia mission (Gaia’s second data set) as well as observations made by Hubble to calculate the weight of the galaxy.
ESA’s Gaia mission was launched in an effort to create the most accurate 3D map of the Milky Way.
By combining the measurements of 34 globular clusters (Gaia data) with data of another 12 distant global clusters (thanks to Hubble) the team was able to determine the mass of the Milky Way “in a way that would be impossible without these two space telescopes.”
Astronomers believe that by accurately determining the mass of the Milky Way they will get “a clearer understanding of where our galaxy is located in a cosmological context.”