To find its edge, scientists took into account the area occupied by both dark and visible matter – and it is much larger than expected.
Our galaxy may be much larger than it looks. Research published on arXiv and led by experts from the University of Durham in England indicates that the Milky Way spans nearly 2 million light-years – with one light year being equivalent to 9.5 trillion kilometers (5.88 trillion miles).
This does not mean that its luminous disk, that is, its visible part, occupies all this space: a study from last year argues that this region of our galaxy measures only 260 thousand light-years.
Just as the Sun influences objects beyond the Solar System, due to its gravitational force and density, the Milky Way’s “invisible” dark matter halo also influences a much larger area – and it was precisely this diameter that researchers recently measured.
To find the edge of the Milky Way, the team conducted computer simulations of how huge galaxies like ours form, focusing on cases in which two giant galaxies appeared side by side (such as the Milky Way and our neighbor Andromeda). This is because these celestial clusters influence each other – and it is the limit of this influence that, for experts, delimits the edge of each galaxy.
With this in mind, astronomers realized that the Milky Way’s influence reaches about 950 thousand light-years from its center, thus delimiting its diameter of 2 million light-years. “In many analyses of the Milky Way halo, its outer boundary is a fundamental constraint. Often the choice is subjective, but as we have argued, it is preferable to define a physically and/or observationally motivated outer edge,” wrote the experts in the article.
Scientists hope to get more data to continue studying the subject, making this measurement increasingly accurate. “There is great hope that future data will provide a more robust and accurate measurement of the edge of the Milky Way and galaxies near it,” they concluded.