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How Do You Weigh a Galaxy?

22 May 2020, 18:08 UTC
How Do You Weigh a Galaxy?
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Title: Evidence for an Intermediate-Mass Milky Way from Gaia DR2 Halo Globular Cluster MotionsAuthors: Laura L. Watkins, Roeland P. Van Der Marel, Sangmo Tony Sohn, and N. Wyn EvansFirst Author’s Institution: University of ChicagoStatus: Published in ApJ, open access on the arXiv
We can’t put it on a digital scale, we can’t hang it on a balance and compare it against something else, so how does one measure the mass of our home galaxy? The authors of today’s paper use measurements of globular clusters in the halo of the galaxy taken from the Gaia satellite to estimate a mass for the Milky Way.

What Is Our Galaxy Made of and Why Should We Weigh It?Our galaxy contains four major parts: the bulge, the disk (which contains the thin disk and the thick disk), the bar, and the halo (see Figure 1). The first three components are made up of baryons, particles that make up protons and neutrons and therefore most of the things around us. The halo, however, is dominated by dark matter, and the percentage of baryonic mass in the halo depends on how much dark matter there is. Dark matter is a mysterious substance that pervades the galaxy, ...

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