Weigh the galaxy! How massive is the Milky Way?

Weigh the galaxy! How massive is the Milky Way?

Get out of the city lights, raise your eyes to the night sky and admire the bright, cloudy stripes of stars that make up our own Milky Way galaxy. We live in a beautiful and large-scale place that hides many secrets. For example, for decades, astronomers have been trying to pinpoint the weight of the galaxy, but estimates range from 700 billion to 2 trillion. times the solar mass.

Weighing a galaxy is an extremely complicated process, especially if you live on its territory. It is as if you had to conduct a census of the population of the country, but the Internet was taken away from you and forbidden to leave the city limits. We are not able to use the giant space scales and do everything the old-fashioned way.

The problem also seems that a large part of the galactic mass remains invisible. Mysterious substance, which does not emit light and is called dark matter, occupies about 85% of the Milky Way. Therefore, the usual counting of stars will not lead anywhere. Researchers have to focus on the orbit of a known object. The method is based on the equations of gravity, derived more than 300 years ago by Isaac Newton. They say that the speed and distance at which a smaller body rotates around a large one is related to the mass of a large object.

That is, you need to look at small satellite galaxies distant hundreds of thousands of light years that revolve around the Milky Way. But even here, things are not so simple, because the orbits of such galaxies span billions of years. Because of this, the researchers decided to resort to a new method that uses supercomputer simulations of virtual universes that can reproduce many aspects of our cosmos. About 90,000 of these simulated satellite galaxies were then compared with data from 9 real galaxies orbiting ours. The choice fell on those whose orbital properties most closely corresponded to real satellite galaxies, and studied the mass simulated.

This allowed us to derive an estimate of the mass of the Milky Way at 960 billion times more than solar. We have an excellent result, but scientists believe that greater accuracy can be achieved. The Gaia satellite from ESA, which recently provided good measurements of the orbital properties of 30 weak dwarf galaxies, will help.

Knowledge of the galactic mass will be useful to many scientists. Astronomers could better calculate the orbits of satellite galaxies, as they depend on the mass of the Milky Way. Heavier have more satellites. So far around our galaxy have noticed 50 rotating neighbors. Also, the true weight will tell you exactly what part falls on the dark matter.

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