Weighing the Milky Way:

[beecee]

https://phys.org/news/2019-03-hubble-gaia-accurately-milky.html

Hubble and Gaia accurately weigh the Milky Way:

March 7, 2019, ESA/Hubble Information Centre:

In a striking example of multi-mission astronomy, measurements from the NASA/ESA Hubble Space Telescope and the ESA Gaia mission have been combined to improve the estimate of the mass of our home galaxy the Milky Way: 1.5 trillion solar masses.

The mass of the Milky Way is one of the most fundamental measurements astronomers can make about our galactic home. However, despite decades of intense effort, even the best available estimates of the Milky Way's mass disagree wildly. Now, by combining new data from the European Space Agency (ESA) Gaia mission with observations made with the NASA/ESA Hubble Space Telescope, astronomers have found that the Milky Way weighs in at about 1.5 trillion solar masses within a radius of 129 000 light-years from the galactic centre.

Previous estimates of the mass of the Milky way ranged from 500 billion to 3 trillion times the mass of the Sun. This huge uncertainty arose primarily from the different methods used for measuring the distribution of dark matter—which makes up about 90% of the mass of the galaxy.

Read more at: https://phys.org/news/2019-03-hubble-gaia-accurately-milky.html#jCp

 

THE PAPER:

https://ui.adsabs.harvard.edu/#abs/2018arXiv180411348W

Evidence for an Intermediate-Mass Milky Way from Gaia DR2 Halo Globular Cluster Motions:

 

Abstract: 

We estimate the mass of the Milky Way (MW) within 21.1 kpc using the kinematics of halo globular clusters (GCs) determined by Gaia. The second Gaia data release (DR2) contained a catalogue of absolute proper motions (PMs) for a set of Galactic GCs and satellite galaxies measured using Gaia DR2 data. We select from the catalogue only halo GCs, identifying a total of 34 GCs spanning 2.0<r<21.12.0<r<21.1 kpc, and use their 3D kinematics to estimate the anisotropy over this range to be β=0.46+0.15−0.19β=0.46−0.19+0.15, in good agreement, though slightly lower than, a recent estimate for a sample of halo GCs using HST PM measurements further out in the halo. We then use the Gaia kinematics to estimate the mass of the MW inside the outermost GC to be M(<21.1kpc)=0.21+0.04−0.031012M⊙M(<21.1kpc)=0.21−0.03+0.041012M⊙, which corresponds to a circular velocity of vcirc(21.1kpc)=206+19−16vcirc(21.1kpc)=206−16+19 km/s. The implied virial mass is Mvirial=1.28+0.97−0.481012M⊙Mvirial=1.28−0.48+0.971012M⊙. The error bars encompass the uncertainties on the anisotropy and on the density profile of the MW dark halo, and the scatter inherent in the mass estimator we use. We get improved estimates when we combine the Gaia and HST samples to provide kinematics for 46 GCs out to 39.5 kpc: β=0.52+0.11−0.14β=0.52−0.14+0.11, M(<39.5kpc)=0.42+0.07−0.061012M⊙M(<39.5kpc)=0.42−0.06+0.071012M⊙, and Mvirial=1.54+0.75−0.441012M⊙Mvirial=1.54−0.44+0.751012M⊙. We show that these results are robust to potential substructure in the halo GC distribution. While a wide range of MW virial masses have been advocated in the literature, from below 1012M⊙1012M⊙ to above 2×1012M⊙2×1012M⊙, these new data imply that an intermediate mass is most likely.