New Method for Measuring Milky Way Shows it’s Much Lighter Than We Realized

A new method has been devised for measuring the mass of the Milky Way galaxy.  It’s more accurate than previous methods and confirms that our galactic home is much lighter than previously estimated. Being made up of stars, clouds of gasses, planets, and other features and surrounded by a halo of dark matter, the Milky Way weighs in between 400 and 780 billion times greater than the mass of the sun.


Using the new measurement method, scientists were able to work out roughly how much dark matter is contained within the Milky Way’s halo. While dark matter is virtually invisible, astronomers know it’s there. Revealing itself only through gravity, dark matter can bend starlight the same way in which a black hole can through gravitational lensing.  Gwendolyn Eadie, the co-author of the study and a Ph.D. candidate in astrophysics at McMasters University in Ontario, Canada, says, “There are all sorts of different facets of research in astronomy where dark matter is necessary. Even though we know the dark matter should be there, [and] we think it should be there, the ratio of dark matter to luminous matter in particular galaxies may be under debate.”

In being able to calculate the mass of the dark matter halo, astronomers will gain a deeper understanding of how the universe evolved and the role dark matter plays in the formation of galaxies.  The way in which the new measurement was taken as by looking at other large things found within the galaxy such as globular clusters. Globular clusters are large, dense groups of stars that are quite big enough to be galaxies, and there are 157 known in the Milky Way.  The new method of measuring uses all the available information there is on these globular clusters and is based on an old technique called a hierarchal Bayesian model.  It will also help astronomers determine where the galaxy ends and where the remainder of space starts.


But, this is just the beginning of the new measuring technique. Scientists and astronomers will continue working on it to make it even more accurate at measuring globular clusters and hence refining the Milky Way mass measurements too. Eadie also mentioned that she would also be receiving data from the European Space Agency’s Gaia spacecraft that will provide us with the measurements of all the stars within the Milky Way, which could also be used to calculate the mass of the Milky Way and use it as a comparison against the new method.


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