According to a team of Canada-based scientists, the Milky Way weighs between 400 to 580 billion solar masses (or 4.0 X 1011 and 5.8 X 1011 solar masses). The sun's mass is two nonillion kilograms times the Earth's mass.

This galactic mass estimate includes matter out to 125 kiloparsecs from the center of the Galaxy (125 kiloparsecs is almost 4 X 1018 kilometers). For reference, when the mass estimate is extended out to 300kpc, the mass is approximately 9 X 1011 solar masses.

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McMaster astrophysicist Gwendolyn Eadie, along with her Ph.D supervisor William Harris and with a Queen's University statistician, Aaron Springford, refined a method for measuring the mass of the Milky Way.

How was the mass measured?

Measuring the mass of a galaxy is particularly difficult because it includes not just celestial bodies, gasses, dust, and other material, but also dark matter.

Eadie, a Ph.D candidate in Physics and Astronomy at McMaster University, has been studying the mass of the Milky Way and its dark-matter component using the velocities and positions of globular star clusters orbiting the Milky Way. The orbits of globular clusters are determined by the galaxy's gravity which is dictated by its dark matter component.

Earlier, Eadie had developed a technique to use globular cluster (GCs) velocities, even when the data was incomplete. Now, Eadie used a statistical method called "hierarchical Bayesian analysis" that includes not only complete and incomplete data, but also incorporates uncertainties in an extremely complex but more complete statistical formula.

Although bayesian statistical methods are not new, their application to astronomy is still in its early stages. According to Eadie, their capacity to accommodate uncertainty while still producing meaningful results opens many new opportunities in the field.