Hubble and Gaia have Measured the Mass of the Milky Way

The data from the Hubble Space Telescope of NASA and the Gaia Satellite of the European Space Agency led to the most accurate measurements of the mass of the Milky Way.

According to previous research, which was conducted several decades back, the mass of our galaxy ranges somewhere between 500 billion and 3 trillion solar masses. The urge to know the mass of the Milky Way more accurately pushed the astronomers to keep looking and it seems as if they did find something extraordinary.

The latest measurements revealed that the Milky Way weighs around 1.5 trillion solar masses (this value is more towards the middle of the range predicted in the earlier study). The research states that a 4-million-solar-mass supermassive black hole is present at the center of our galaxy and all the 200 billion stars constitute a really small fraction of the galaxy. Most of the remaining mass is locked inside the Dark Matter, an invisible substance that keeps the stars in their respective galaxies. Roeland van der Marel, an Astronomer at the Space Telescope Science Institute (STScI), talked about the reasons for knowing the mass of the Milky Way more accurately and said,

“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. Not knowing the precise mass of the Milky Way presents a problem for a lot of cosmological questions.”

Mass of the Milky Way in Comparison to other Galaxies

The lightest galaxies of our universe have a mass of about one billion solar masses. On the other hand, the heaviest ones are in the range of 30 trillion solar masses. In contrast to that, a mass of 1.5 trillion solar masses is quite normal for a galaxy as bright as the Milky Way. Consequently, it can be said that our galaxy is on the beefier side when compared to other galaxies of the universe.

How did the Researchers found the Mass of the Milky Way?

Researchers measured the 3-dimensional movement of globular star clusters to determine the influence of dark matter on these spherical islands of stars. It allowed them to measure the mass of this mysterious form of matter (ultimately the mass of the Milky Way). In contrast to previous studies where measurements were taken along the line of clusters, both Hubble and Gaia recorded the sideways movement of the globular clusters. As a result, the data gathered in the latest research is considered much more reliable than the previous versions.

The observations of Gaia and Hubble are complementary to each other. The latter of the two can observe far-off stars but has a smaller field of view while Gaia created a three-dimensional map of astronomical objects (including globular clusters) throughout the Milky Way. For the sake of this research, astronomers considered Hubble’s measurements for 12 clusters out to 130,000 light-years. Similarly, Gaia’s measurements for 34 globular clusters out to 65,000 light-years were used for this study. Upon combining these measurements, scientists were able to predict the distribution of the mass of the Milky Way out to nearly 1 million light-years from Earth. Laura Watkins, the Lead Author of the study from the European Southern Observatory, elaborated their findings by saying,

“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.”

Entire Mass of the Milky Way

Researchers performed rigorous calculations on the measurements of globular cluster motion from Hubble and Gaia to determine the entire mass of the Milky Way. It was found that some of the earliest globular clusters that formed some hundred million years after the Big Bang were present much before the construction of spiral disk (the part of space where our Sun and Solar System is located) of our galaxy. Tony Sohn, an Astronomer at STScI who led the observations of the Hubble Space Telescope, referred to that in the following words:

“Because of their great distances, globular star clusters are some of the best tracers astronomers have to measure the mass of the vast envelope of dark matter surrounding our galaxy far beyond the spiral disk of stars.”

It is a massive development that could prove extremely beneficial for astronomers as they strive to improve their understanding of the evolving universe.