Astronomers have found the edge of our galaxy
When we talk about galaxies, it’s really difficult to imagine its real sizes. For example, the Milky Way, our home and home for 100–400 billion stars, has a visible diameter of 150,000–200,000 light-years, which is enormous.
However, scientists found that Milky Way stretches nearly 2 million light-years across, which is more than 15 times wider than its luminous spiral disk.
Alis Deason, an astrophysicist at Durham University of England, and her colleagues have used nearby galaxies to locate the Milky Way’s edge. According to her calculations uploaded on arXiv.org, the precise diameter is 1.9 million light-years, give or take 0.4 million light-years.
To find the galaxy’s edge, Alis Deason and her team conducted computer simulations of Milky Way — mass haloes — ELVIS (The «Exploring the Local Volume in Simulations), APOSTLE (A Project Of Simulating The Local Environment), the Auriga.
ELVIS (The «Exploring the Local Volume in Simulations). It consists of 48 simulations of Galaxy-size haloes, which were designed to model the Local Group environment (LG). Twenty four of them are paired in configurations similar to the Milky Way and Andromeda (M31). The remaining haloes (24) are isolated, mass-matched analogues, which are resimulated in the same resolution as the paired ones. As a result, we get a sample of 48 high-resolution haloes.
APOSTLE (A Project Of Simulating The Local Environment) is another project used for the research. It is a suite of high resolution, hydrodynamic simulations that includes 12 halo pairs. The candidates were selected to have paired configurations similar to LG; however, the selection criteria are different from the ELVIS suit, with the main difference being the total masses of haloes: the APOSTLE has lower halo masses. The simulations were performed on three resolution levels.
The Auriga. This suite consists of cosmological hydrodynamical zoom-in simulations of isolated Milky Way-mass haloes.
With the help of these programs, Deason and her colleagues modeled Milky Way’s dark matter based on radial velocity and density to define the edge of the Milky Way’s dark matter.
As a result, it was shown that the radial velocity of dwarf galaxies beyond the edge of the galaxy’s dark halo dropped noticeably.
After they compared their results to the telescope observations, Deason and her team found a similar plunge in the speeds of small galaxies near the Milky Way. The calculations made by the researchers showed the distance of about 950,000 light-years from Milky Way’s center, marking the galaxy’s edge. If we double this number, we’ll get 1,9 million light-years.
According to the study, there is a great hope that future data will provide a more accurate measurement of the Milky Way’s edge and nearby Milky Way-mass galaxies.
