NASA says the Milky Way weighs 1.5 trillion solar masses

Astronomers weigh the galaxy with Hubble and Gaia

Previously, estimates for the mass of the Milky Way were all over the map, ranging from a paltry 500 billion solar masses to 2 or 3 trillion masses.

Our galaxy has been put on a set of mathematical scales by scientists who have discovered the weight of the Milky Way.

This artist's impression shows a computer generated model of the Milky Way and the accurate positions of the globular clusters used in this study surrounding it. Scientists used the measured velocities of these 44 globular clusters to determine the total mass of the Milky Way, our cosmic home. This is exactly what an global team of astronomers have done and instead of looking for something that has escaped all detection so far, they measured the velocities of globular clusters to work out the mass of the Milky Way.

To weigh the galaxy, the team augmented Gaia measurements for 34 globular clusters out to 65,000 light-years, with Hubble measurements of 12 clusters out to 130,000 light-years that were obtained from images taken over a 10-year period. The new finding of 1.5 trillion solar masses puts the Milky Way among the universe's larger galaxies.

"We know from cosmological simulations what the distribution of mass in the galaxies should look like, so we can calculate how accurate this extrapolation is for the Milky Way", said Laura Watkins of the European Southern Observatory in Garching, Germany, lead author of the combined Hubble and Gaia study. Gaia was launched on 19 December 2013 and is located at the L2 Lagrange point - the same location that the upcoming NASA/ESA/CSA James Webb Space Telescope will have.

That tiny portion of weight also includes the enormous 4-million-solar-mass supermassive black hole at the center of the Milky Way. By better understanding the universe close by, we can better comprehend the galaxies a few more light-years away.

Until now, not knowing the precise mass of the Milky Way has presented a problem for attempts to answer a lot of cosmological questions.

The study was presented in the paper "Evidence for an Intermediate-Mass Milky Way from Gaia DR2 Halo Globular Cluster Motions", which will be published in The Astrophysical Journal.

"The more massive a galaxy, the faster its clusters move under the pull of its gravity", explained Professor Wyn Evans, of the University of Cambridge in England.

"Most previous measurements have found the speed at which a cluster is approaching or receding from Earth, that is the velocity along our line of sight".

And as far as galaxies go, ours is a heavy one compared with others, but it's also appropriate considering how bright it is. The trimmest galaxies are about a billion solar masses, and the morbidly obese ones are 30,000 times heftier at 30 trillion solar masses.

This globular cluster, NGC 4147, seen with the NASA/ESA Hubble Space Telescope, was one of many which were used by astronomers to measure the total mass of the Milky Way. Astronomers use the knowledge we can get of the Milky Way to learn about more distant galaxies that we can't study in such detail.

ESA's Gaia satellite (pictured) and Hubble provided data on 46 globular clusters, masses of hundreds of thousands of stars that swarm around the Milky Way's centre.

"We were lucky to have such a great combination of data". Dark matter makes up 90 percent of the galaxy's mass, but European Southern Observatory's Laura Watkins reveals that it is not possible to see and observe dark matter directly, which made it hard to get an accurate figure for the scientists.

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