How much does our galaxy weigh? About 700 billion suns

A Ph.D. student in physics at a Canadian university attempted to measure the Milky Way’s mass. How dense is it? Equivalent to about 700 billion suns. Gwendolyn Eadie, a Ph.D. student in physics and astronomy at McMaster University in Hamilton, Canada, presented her research at a Canadian Astronomical Society conference yesterday.

Previous estimates of our galaxy’s mass have fallen between 100 billion to 1.6 trillion times the mass of our sun. The Huffington Post reports that Eadie and a professor of physics and astronomy at McMaster, William Harris, broached the inquiry by formulating a novel way to calculate the Milky Way’s dark matter, apparently invisible and undetectable.

Led by Eadie and Williams, a team of researchers observed the positions and velocities of many globular star clusters that orbit in the galaxy. Scientists released a statement that “the orbits of globular clusters are determined by the galaxy’s gravity, which is dictated by its massive dark matter component.”

Not only is the study’s method unique but it’s also one of the most comprehensive analyses up to this point. Eadie told the Guardian, “With our estimate, it seems that dark matter makes up about 88% of the Milky Way’s mass.” That leaves the rest of the weight to every other matter filling in the void—stars, planets, gas, moons, and dust.

These new observations could clue scientists into our galaxy’s mysterious beginnings. Eadie told National Geographic that “People who study the evolution of galaxies look at how the mass relates to its evolution,”  and, “If we have a better handle on what the mass of the Milky Way is, we can understand how it and other galaxies form and evolve.”

As speculation and research continue, scientists are left with knowing that the sun has a mass roughly 330,000 times that of the Earth, and the Milky Way nearly 700 billion times that of the sun. To put the size into further perspective, our galaxy was recorded to be 100,000 light years across, or 587,849,981,000,000,000 miles long.