The Milky Way has gained weight
Our galaxy is at least 28 % heavier than we thought. That is the conclusion of a research project by the University of Arizona, USA, and the University of Cambridge.
Until now, astronomers have used observations from satellite galaxies to calculate the mass. Satellite galaxies are bound by the gravity with which the mass of the Milky Way influences them, and when astronomers know the distance to the galaxies and the speed at which they orbit the Milky Way, they can calculate the mass of our galaxy. In recent years, calculations have shown results of 600-750 billion times the Sun’s mass. However, those results are doubtful, as rather than circular, the satellite galaxies have elliptical orbits, and so, their speeds vary, depending on their position in the orbit. When they are the furthest away from the Milky Way, they travel more slowly than close by.
Instead of using the speed of the satellite galaxies, the scientists use their angular momentum, which is the same all through the orbit, because it depends on both speed and distance. According to the new method, our galaxy weighs 960 billion times more than the Sun, or 28% more than earlier calculations. The new knowledge helps astronomers seeking dark matter, which we can only measure by looking at the gravity, with which the matter influences its surroundings.
The mass of the Milky Way can be calculated by examining the motion of the galaxies that orbit it – such as the Large Magellanic Cloud (insert).