Published: Sun, March 10, 2019
Research | By Raquel Erickson

Researchers may have found the weight of the Milky Way

Researchers may have found the weight of the Milky Way

With the help of Gaia, scientists have been able to come up with one of the most accurate measurements yet of our galaxy's mass and its a huge 1.5 trillion solar masses and most of which is dark matter.

Previous estimates of the mass of the Milky Way ranged between 500 billion and 3 trillion times the mass of the Sun. 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.

"The more massive a galaxy, the faster its clusters move under the pull of its gravity", said Dr. N. Wyn Evans, from the University of Cambridge. While previous measurements have been along the line to sight to globular clusters, astronomers know the speed at which a globular cluster is approaching or receding from Earth. They combined data collected by NASA's Hubble telescope and the European Space Agency's Gaia observation satellite. A tiny, tiny fraction is the monstrous supermassive black hole at the center of the galaxy, coming in at four to five million solar masses, plus the stuff like the planets, and you and I. The remaining 90-odd per cent is dark matter. The ESA's Gaia mission is designed to create the most precise 3D map of the astronomical objects in the galaxy and track how they move over time.

Plait reports that the team had to estimate the mass of the galaxy beyond the 130,000 light year mark, especially the halo of dark matter that is believed to surround it.

The Hubble Space Telescope is a project of global cooperation between ESA and NASA. Now, scientists have solved one of the riddle of the Milky Way's weight by combining fresh data from the Gaia mission and the Hubble Space Telescope. It's hard to see it all at once, buried as we are within one of its spiral arms. Those clusters orbit near the center of our galaxy. That means there's a pretty large margin of error in the estimate, meaning the true mass of the Milky Way may be somewhere between 0.79 and 2.29 trillion solar masses-but the current estimate is a good start.

The April release of data included data on globular clusters as far away as 65,000 light years from Earth. "By combining Gaia's measurements of 34 globular clusters with measurements of 12 more distant clusters from Hubble, we could pin down the Milky Way's mass in a way that would be impossible without these two space telescopes". Accurately determining the mass for the Milky Way gives us a clearer understanding of where our galaxy sits in a cosmological context. Since Hubble has been observing some of these objects for ten years, it was also possible to accurately track the velocities of these clusters as well.

If you have ever been to a school fete and seen a large, glass jar filled with candies, labelled "guess how many jelly beans there are", chances are you have studied it meticulously to try and work out that magic number.

The global team of astronomers in this study consists of Laura L. Watkins (European Southern Observatory, Germany), Roeland P. van der Marel (Space Telescope Science Institute, USA, and Johns Hopkins University Center for Astrophysical Sciences, USA), Sangmo T. Sohn (Space Telescope Science Institute, USA), and N. Wyn Evans (University of Cambridge, UK). Amazingly, only a few percent of this is down to the approximately 200 billion stars in our galaxy; the rest we still can't see, just infer.

"We were lucky to have such a great combination of data", explained Roeland P. van der Marel (Space Telescope Science Institute, USA).

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