It seems like everything in space is orbiting something else. Moons orbit planets, planets orbit stars, and stars move around the centers of galaxies. But what about the galaxies themselves and more particularly our galaxy, the Milky Way?
Galaxies in the Local Group
To answer this question, it is essential to understand how orbits work. When two objects are in orbit around each other, they exert a mutual gravitational attraction that keeps them linked. These objects thus gravitate around their common center of mass, a point where it could be balanced on a finger if we could reduce said system. However, in systems like the Earth and Moon where one of the objects is much larger than the other, the center of mass is often within the larger body, making the orbit of the smaller circular object around the larger one.
On a larger scale, orbits become more complex. Our Milky Way is part of a group of galaxies known as the Loca Groupl which includes the Andromeda Galaxy, a small spiral galaxy called the Triangle, and several dwarf galaxies, such as the Large and Small Magellanic Clouds. The Milky Way and Andromeda are the two largest galaxies in this group and their comparable masses place the center of mass somewhere between them.
The future collision
Unlike planetary orbits, the Milky Way’s orbit is neither circular nor elliptical. According to Sangmo Tony Sohn, an astronomer at the Space Telescope Science Institute, the two galaxies lie on mainly radial orbits, which means that they move directly towards each other under the effect of their gravitational attraction. This dynamic means that these two galaxies will eventually collide in about 4.5 billion years. They will initially pass through each other without their stars colliding, due to the immense distances separating them. Eventually, this interaction will result in the two objects merging into a single large galaxy.
Larger scale orbits
At even larger scales, orbits become less defined. The Local Group, of which the Milky Way is a part, is moving towards the Virgo cluster, a gigantic collection of several hundred galaxies located approximately 65 million light years away. However, due to the expansion of the Universe, the Local Group will never join this clusterbecause this expansion pushes galaxies apart faster than gravitational attraction brings them together.
In summary, the Milky Way does not orbit a specific object, but revolves around a common center of mass with the Andromeda Galaxy. It is also part of a complex dynamic of gravitational attractions with other members of the Local Group.
