Astronomists Discover Edge of Milky Way

By: Noemi Elliott

A team of astronomers at Durham University in England determined the Milky Way’s diameter– 1.9 million light-years (within an error bound of 0.4 million light-years). Led by astrophysicist Alis Deason, the team published a scientific report on February 21 detailing the process and discovery.

Utilizing computer simulations, the team studied the formation of a galaxy to define its “edge,” determined by a drop in the velocity or density, resulting in a dark halo. Additionally, they focused on the side-by-side formation of galaxies, such as the Milky Way and Andromeda, and the gravitational pull exhibited between them.

“In many analyses of the Milky Way halo, its outer boundary is a fundamental constraint,” included the researchers in their paper. “Often, the choice is subjective, but as we have argued, it is preferable to define a physically and/or observationally motivated outer edge. Here we have linked the boundary of the underlying dark matter distribution to the observable stellar halo and the dwarf galaxy population.”

With the assistance of a telescope, Deason observed similar drops– at around 950,000 light-years from the center of the Milky Way– in smaller galaxies near the Milky Way.

The simulations also determined that while the Milky Way’s mass is composed largely of dark matter, there is a probability of the existence of stars around the edges. “Both have a well-defined edge,” noted Deason. “The edge of the stars is very sharp, almost like the stars just stop at a particular radius.”

In the future, the methodology of Deason’s discovery may be applied to different experiments within the field. The diameter will also support astronomers in determining other galactic properties.

“There is great hope that future data will provide a more robust and accurate measurement of the edge of the Milky Way and nearby Milky Way-mass galaxies than the one we have presented here. In this work we have focused on Milky Way mass haloes in a ΛCDM cosmology, but a similar analysis can be extended to wider mass scales and applied to different cosmologies or dark matter models,” concluded the paper.





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