The Galaxy we live in has turned out to be much more massive than we initially thought.
According to the latest, most accurate measurements of the size and mass of our home galaxy the Milky Way, we live in one really, really, really, big place.
According to astronomers, the Milky Way is freakishly massive.
Well, according to the latest estimates, about 1.5 trillion Suns’ worth of solar masses, within a radius of approximately 129,000 light-years.
As it turns out, this is more than two times the previous estimate.
In 2016, astronomers had revealed that the Milky Way’s weigh was just around 700 Billion Solar Masses.
But new data from ESA’s Gaia mission, which has helped accurately map the Milky Way in 3D has given us the most detailed cosmic chart of the galaxy, completely changing everything we thought about the Milky Way.
So how do we know the Milky Way is so Massive?
Thanks to data from Hubble and Gaia, scientists were able to calculate the galaxy’s size and mass, taking into consideration the orbital motion of local groups of stars, called globular clusters.
As explained by a statement from Hubble, “Previous estimates of the mass of the Milky Way ranged from 500 billion to 3 trillion times the mass of the Sun.”
“And this uncertainty arose primarily from the different methods used for measuring the distribution of dark matter — which makes up about 90% of the mass of the galaxy.”
“We just can’t detect dark matter directly,” explains Laura Watkins (European Southern Observatory, Germany), who led the team performing the analysis.
“That’s what leads to the present uncertainty in the Milky Way’s mass — you can’t measure accurately what you can’t see!”
Dark Matter remains as one of the most elusive cosmic phenomena out there. We know it exists, but it has never been observed, yet it greatly influences the universe.
Since we know so little about Dark Matter, astronomers had to use clever new methods in order to find out how much our galaxy weighs.
This relied primarily on calculating the velocities of globular clusters — dense star clusters that orbit the spiral disc of the galaxy at great distances.
“The more massive a galaxy, the faster its clusters move under the pull of its gravity” explains N. Wyn Evans (University of Cambridge, UK).
“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. However, we were able to also measure the sideways motion of the clusters, from which the total velocity, and consequently the galactic mass, can be calculated.”
The data ESA’s Gaia mission gathered, specifically Gaia’s second data set was crucial for the new study.
Gaia was developed to create the most accurate three-dimensional chart of astronomical objects across the Milky Way and to track their motions.
The second data set features measurements of globular clusters as far as 65 000 light-years from Earth.
“Global clusters extend out to a great distance, so they are considered the best tracers astronomers use to measure the mass of our galaxy,” said Tony Sohn (Space Telescope Science Institute, USA), who led the Hubble measurements.