Astronomers Calculate Mass of Milky Way Galaxy for First Time

  • Astronomers Calculate Mass of Milky Way Galaxy for First Time

Astronomers Calculate Mass of Milky Way Galaxy for First Time

So to turn this around, by measuring their speeds, we can estimate the mass of the Milky Way. It's hard to see it all at once, buried as we are within one of its spiral arms. "We use the clusters to estimate the mass of the Milky Way, not the mass of the clusters themselves".

The result was that our home galaxy weighs around 1.5 trillion solar masses within a radius of 129,000 light years around the galactic center.

Previous researches used several observational techniques that provided estimates for the galaxy's mass ranging between 500 billion to 3 trillion solar masses. This uncertainty is primarily a function of the different means astronomers and physicists used to measure the distribution of dark matter through the galaxy.

'That's what leads to the present uncertainty in the Milky Way's mass - you can't measure accurately what you can't see!'

They also measured the three-dimensional movement of globular star clusters - isolated spherical islands each containing hundreds of thousands of stars each that orbit the center of our galaxy.

"The more massive a galaxy, the faster its clusters move under the pull of its gravity", said N. Wyn Evans of the University of Cambridge, UK.

The scientists used Gaia's second data release - which includes measurements of globular clusters as far as 65,000 light-years from Earth - as a basis for their study. And Watkins tells Dvorsky at Gizmodo that Gaia, which is expected to map the sky for another decade, will continue to reveal more globular clusters and help astronomers continue refining the weight estimate of the galaxy.

Observations from Hubble allowed faint and distant globular clusters, as far as 130,000 light-years from Earth, to be added to the study.

Now scientists have done just that, using new data from the Hubble Space Telescope combined with the Gaia spacecraft.

The Hubble telescope (pictured) provided data for the study. The objects (in this case globular clusters) orbit inside a larger object (in this case the Milky Way). As Hubble has been observing some of these objects for a decade, it was possible to accurately track the velocities of these clusters as well.

"We want to know the mass of the Milky Way more accurately so that we can put it into a cosmological context and compare it to simulations of galaxies in the evolving universe", Roeland van der Marel, head of the Wide Field Infrared Survey Telescope mission office at the Space Telescope Science Institute, said in a statement.

[1] Globular clusters formed prior to the construction of the Milky Way's spiral disk, where our Sun and the Solar System later formed.

And understanding the total mass of our galaxy, and how its stars' mass stack up against its dark matter, can help astronomers answer important cosmological questions about how galaxies like ours evolve. With only one component of the velocity available, the estimated masses depend very strongly on the assumptions for the sideway motions. Image credit: NASA / ESA / Hubble / L. Calçada. But as Phil Plait at Bad Astronomy blog notes, measuring the mass of the Milky Way is much more hard because we are inside it and can't get the big picture, literally. The mission has release two lots of data thus far: Gaia Data Release 1 in 2016 and Gaia Data Release 2 in 2018.

Together, Gaia and Hubble could capture the sideways motion of the clusters, which shows gravitational acceleration. 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.