Our home galaxy, the Milky Way, is big. Just how big it really is continues to be a fairly open question in the astronomy community.
Researchers had previously estimated that the total mass of the Milky Way is between 500 million to 3 trillion solar masses. This wide range and uncertainty come from how researchers factor in dark matter – the invisible material that supposedly occupies 85 percent of all matter in the universe – which still remains unmeasurable.
Now, researchers at the European Southern Observatory (ESO) have managed to accurately weigh the galaxy and all the dark matter in it. They claim that the Milky Way weighs in at a hefty 1.5 trillion times the mass of the Sun.
The ESO team came up with a clever workaround to measure the Milky Way’s mass without directly observing dark matter. They set up NASA’s Hubble Space Telescope and the ESA’s Gaia spacecraft to pick up on how fast globular star clusters that orbit the Milky Way galaxy move over time. These clusters are spheres of densely-packed stars that are part of the Milky Way in some ways, but they also orbit independently, as a satellite star cluster.
The team looked at 46 such globular clusters orbiting the Milky Way — 34 of them using the Gaia telescope and 12 using Hubble. The most distant of these clusters was roughly 129,000 light years away from Earth.
Since these clusters are tightly bound to the Milky Way galaxy by gravity, their velocity is a direct indicator of the galaxy’s mass. The more the mass, the faster the clusters will orbit it. The scientists cross-examined 46 clusters and arrived at a total mass of 1.5 trillion Suns.
This new and “more accurate” measurement also falls neatly in the middle of the range predicted in past studies. Having an accurate measurement is important for our understanding of the universe as well as calculations made about them. The Milky Way is one single galaxy, but it happens to be the only one we can study using the technology we have today.
It is also likely going to affect how we understand dark energy – the distribution and effects of which are still fairly unknown. Dark matter is a huge area of research today since it is linked to how the majority of structures in the universe has formed, including the Milky Way.
It is thought that these objects work similarly to our own galaxy. And so, having an accurate number for the galaxy’s mass goes a long way towards solving the larger astronomical puzzle.