Scientists Just 'Weighed' The Milky Way, Dark Matter And All

The vast majority of our galaxy is undetectable, but that didn't stop these researchers from devising a novel way to measure it.

Our home galaxy is a star-studded monstrosity, measuring some 100,000 light years (587,849,981,000,000,000 miles) across.

Calculating the weight of something so colossal seems beyond the realm of possibility. But not for Gwendolyn Eadie, a Ph.D. student in physics and astronomy at McMaster University in Hamilton, Canada.

Eadie and her team presented new research at a Canadian Astronomical Society conference Tuesday that shows the Milky Way has a mass equivalent to about 700 billion suns.

Trying to measure the weight of a galaxy is no easy feat, especially when peering from the inside out. Previous estimates about the Milky Way's mass have ranged from 100 billion to 1.6 trillion times that of our own Sun.

But Eadie and William Harris, a professor of physics and astronomy at McMaster, approached the query from a new angle by devising a novel way to measure the galaxy's dark matter -- that which is invisible and undetectable. To arrive at their current estimate, the team studied the positions and velocities of numerous globular star clusters that orbit the Milky Way. As the authors note in a release, "the orbits of globular clusters are determined by the galaxy's gravity, which is dictated by its massive dark matter component."

According to early reviews, their approach is one of the most thorough analyses to date.

“With our estimate, it seems that dark matter makes up about 88% of the Milky Way’s mass," Eadie told The Guardian. 

The rest of the weight are the things you might expect -- stars, planets, gas, moons and dust.

A person watches the Milky Way while standing inside Utah's Delicate Arch.
A person watches the Milky Way while standing inside Utah's Delicate Arch.

Ultimately, determining the Milky Way's total mass could provide scientists with clues about its long and mysterious history.

"People who study the evolution of galaxies look at how the mass relates to its evolution," Eadie told National Geographic. "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."

Until then, rest easy knowing that the sun has a mass roughly 330,000 times that of the Earth, and the Milky Way has a mass some 700 billion times that of the sun.

And you, little Earthling, are not the center of the universe. 

CORRECTION: An earlier version of this story said McMaster University was in Ottawa. In fact, it is in Hamilton. 



Stunning Milky Way