Scientists estimate mass of the Milky Way galaxy at around 1.5 trillion solar masses

Previous estimates ranged from 500 billion to 3 trillion solar masses

A computer generated model of the Milky Way and globular clusters.Image: ESA/HUBBLE/NASA/L. Calcada

Dev Kundaliya
08 March 2019

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Astronomers have improved their estimate of the mass of the Milky Way Galaxy by studying the movements of star clusters orbiting the Milky Way.

New calculations suggest that the mass of the Milky Way is around 1.5 trillion solar masses, within a radius of 129,000 light-years from the centre of the galaxy.

Previous estimates for our galaxy's mass ranged widely from 500 billion to three trillion solar masses. According to scientists, huge uncertainty in those estimates arose due to the use of different methods for measuring the distribution of dark matter within the galaxy. But, latest estimate is far more accurate, scientists claim, and lies in the middle of the previous range.

In the current study, astronomers used new data sets which included the weight of dark matter. They combined data collected by NASA's Hubble telescope and the European Space Agency's Gaia observation satellite.

These two space telescopes come with different features that balance each other nicely. Gaia telescope can scan a much larger region of sky but can't see at relatively larger distances.

Gaia mission aims to create a 3D map of Milky Way and to provide details about its composition and formation. Scientists expect Gaia to eventually provide accurate positional and radial velocity measurements and to produce a kinematic and stereoscopic census of approximately one billion stars in the galaxy and throughout the Local Group.

Hubble, in comparison, is capable of seeing further away, although it can scan only a small area at a time.

Astronomers used the data from these two telescopes to measure the motion of 46 "globular clusters" - the distinct groups of stars orbiting the centre of Milky Way. The new measurements enabled the team to determine the gravitational pull exerted on those clusters as well as the mass that generated the pull.

Astronomers used these calculations to extrapolate outward and finally estimate the mass of the Milky Way.

"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.

According to researchers only a few per cent of the Milky Way's total mass is contributed by around 200 billion stars in the Milky Way. The rest of the galaxy's mass is locked up in invisible dark matter.

The findings of the study are published in the Astrophysical Journal.