How much does the Milky Way weigh? Scientists get closer to an answer

By Brooks Hays   |   Jan. 9, 2017 at 11:54 AM
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HAMILTON, Ontario, Jan. 9 (UPI) -- What is the true mass of the Milky Way? New research has helped astronomers arrive at their most accurate estimate yet.

According to a team of researchers at McMaster University and Queen's University, both in Canada, the Milky Way weighs between 400 to 580 billion solar masses. The sun's mass is 330,000 times the mass of Earth, or 2 nonillion -- a 2 followed by 30 zeroes -- kilograms. In pounds, the sun's mass is 4.18 nonillion.

When weighing the Milky Way, there are the masses of hundreds of billions of stars, planets, moons, gas and dust. Estimating the collective weight of visible material is the easy part, however. The difficult part comes when estimating the mass of dark matter -- the stuff astronomers can't see, yet to be directly detected in a lab or in space.

The weight of dark matter must be inferred by the gravitational influence of the Milky Way on the position and movement of the globular star clusters that orbit our galaxy. Measuring the movement of globular clusters presents its own challenges.

To measure a globular cluster's "proper motion," astronomers have to chart its path along both the line-of-sight and across the plane of the sky. Astronomers have done this for only a few globular clusters.

Researchers built a new statistical model designed to account for the uncertainty of motion values attributed to globular clusters. The model uses Bayesian statistical methods to treat cluster positions and velocities as parameters, not fixed values.

"As the era of Big Data approaches, I think it is important that we think carefully about the statistical methods we use in data analysis, especially in astronomy, where the data may be incomplete and have varying degrees of uncertainty," McMaster astrophysicist Gwendolyn Eadie said in a news release.

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