US, WASHINGTON (ORDO NEWS) — Astrophysicists from the UK , Germany , USA and Canada using the Gaia space telescope for the first time were able to determine the size of our Galaxy by measuring the diameter of the halo of dark matter – the spherical region over which the gravitational field of the Milky Way extends.
Results of the study submitted for publication in the journal Monthly Notices of the Royal Astronomical Society, and placed in the library preprints arXiv.org.
Astronomers successfully observe other galaxies, but they cannot photograph the Milky Way, since they are inside it. Therefore, when assessing the size of our Galaxy, they usually come from the distance to its most distant objects.
However, such an estimate gives only the boundaries of the galactic disk with a diameter of about 260 thousand light years. But, just as the boundaries of the solar system extend much further than the Kuiper belt and include the entire region of the gravitational influence of the sun, so the boundaries of the galaxy are much further than the visible region of the galactic disk.
Calculations based on the Gaia space telescope mapping data showed that the invisible halo of dark matter rotating around the supermassive black hole Sagittarius A * extends for 950 thousand light-years.
For the seventh year, the Gaia telescope has carefully recorded the position of all moving objects in our Galaxy, their radial velocities and the change in the distances between stars. The task of the project is to build an accurate 3D map of the Milky Way, but for this it is important to know its dimensions.
British, German, American and Canadian astrophysicists have joined forces to determine the distance to the outer borders of the halo of dark matter. They proceeded from the fact that the stars on the outer edges of the galactic disk move much faster than they should, if based on the gravitational influence of only visible matter. Scientists interpreted the additional gravitational impact as an external halo emanating from dark matter.
Then they conducted high-resolution simulations of halos of dark matter of galaxies with mass of the Milky Way – both individually and as part of the Local Group (a small group of galaxies with a diameter of about 9.8 million light-years, which includes the Milky Way, the Andromeda galaxy (M31) , Triangle (M33) and several dozen smaller ones).
Taking into account radial velocities (orbital velocities of objects moving around the center of the Galaxy at various distances) and density, the authors determined the boundary beyond which the speed of dwarf galaxies drops markedly.
The radial distance to this boundary was about 292 kiloparsecs, or 950 thousand light years, and the total size of the Milky Way, or its diameter, is 1.9 million light years.
These results were the first measurement of the external dimensions of our Galaxy. They will still be specified, but now, according to the authors, they can be used as boundary parameters in many studies and theoretical constructions.
“In many analyzes of the Milky Way halo, its outer boundary is a fundamental limitation. Often, scientists are guided by a subjective choice, but it is preferable to determine the outer edge physically. We have linked the distribution of dark matter with the observed stellar halo and a population of dwarf galaxies,” the authors of the article write.
“We hope that future data will provide a more reliable and accurate measurement of the boundaries of the Milky Way and nearby galaxies,” they note.
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