How massive is the Milky Way? New study has the answer.

Astrophysicists finally have an accurate measurement for the weight of the Milky Way – approximately 7 x 10¹¹ solar masses, or 700 billion times the mass of our Sun.

Gwendolyn Eadie, a physicist at McMaster University, has been working on calculating the mass of the Milky Way for some time, and in a press release, she noted that “our galaxy isn’t even the biggest galaxy.”

Computing the mass of any galaxy is challenging. A galaxy contains not just easily detectable objects like stars, planets, gases and dust, but also an unknown amount of dark matter, a strange and invisible kind of matter that is still mostly theoretical in nature. Astrophysicists have inferred its presence through observed gravitational affects on visible objects.

How can you calculate the mass of the Milky Way?

To calculate the mass of the Milky Way, including its dark matter, Eadie used the velocities and locations of globular star clusters (GCs) that circle the Milky Way.

The orbits of globular clusters are established by the galaxy’s gravity, which is dictated by its significant dark matter element. The study is based on a novel method for using globular cluster (GCs) velocities.

The overall velocity of a GC must be assessed in two directions: one along our line-of-sight, and one along the plane of the sky. Unfortunately, scientists have not yet assessed the proper motions of all the GCs around the Milky Way.

Eadie, however, developed a way to use velocities that are only partially known, along with the velocities that are fully known, to approximate the mass of the galaxy. Her technique also predicts the mass held within any distance from the center of the galaxy, which makes her findings easy to compare with other analyses.

Despite all the work she has put in, Eadie said all her calculations have made her appreciate skywatching even more.

“Every so often I think, ‘I’m measuring the mass of the Milky Way.’ That’s pretty neat,” she said.

Back in March, scientists said they may have detected the first example of dark matter annihilation, a phenomenon that would prove the existence of dark matter. Theoretically speaking, dark matter comes in both a regular form and an anti-matter form. When these two forms collide, they annihilate and a new high-energy particle is formed, like a photon or a gamma-ray.

The research team said they found how gamma-ray emission from dark matter annihilation was distributed throughout the Galactic Center region of the Milky Way.

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Image credit: Thinkstock

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