The Moon orbits the Earth and the Earth orbits the Sun. This may lead you to wonder if our galaxy revolves around anything?
The Milky Way is one of two massive galaxies that comprise the Local Group, which encompasses around fifty galaxies. Andromeda, our nearest galactic neighbor, is also involved. Our two galaxies are slowly circling one other.
Mass and Orbiting
If you want to know how any two objects will orbit each other, you need to know their mass, distance between them, and speed relative to each other. You may use this knowledge to predict the route the two items will take with each other.
The masses of your two objects define where they will circle. The center of mass is the point in space with an equal distribution of mass around it.
The Sun holds practically all of the mass in a system like the Sun and the Earth – the mass of the Earth being so far away doesn’t shift the center of mass all that much. The Earth only moves the Earth-Sun center of mass slightly away from the Sun’s center of mass.
However, if the two objects have similar masses but are widely apart, the center of mass is really between them, in space. This is the situation with Pluto and its moon Charon, which are near enough in mass to circle a point above Pluto’s surface.
The same may be said for the Milky Way and Andromeda. They’re both enormously huge things that are quite far apart, but they’re gravitationally linked.
They are in orbit at a point in the center of the space between the Milky Way and Andromeda because neither can escape the gravitational pull of the other. Our galaxy and Andromeda will ultimately collide at this location, which is the center of mass between the two.
The Merger
The Andromeda galaxy is now speeding toward our Milky Way at around 70 miles per second. With this in mind, our union will take place in five billion years. However, a fresh study released in the peer-reviewed Astrophysical Journal in August 2020 revealed that the collision between our galaxies is already occurring.
The Andromeda galaxy, our Milky Way, and other galaxies are all surrounded by a huge envelope of gas, dust, and stray stars known as a galactic halo. The halos of galaxies are faint, so faint that spotting them is difficult. The halo of the Andromeda galaxy was estimated by looking at how much light is absorbed from background quasars. They were shocked to discover that the halo of the Andromeda galaxy extends well beyond its observable borders.
It does reach half the distance to our Milky Way and even beyond in other directions.
It turns out that we can’t simply measure the properties of our galaxy’s halo from our vantage point inside the Milky Way. However, because the two galaxies are so similar in size and appearance, astronomers believe the Milky Way’s halo will be as well.
In other words, the faint halos of the galaxies appear to have begun to touch one another. Thus, in a sense, the collision between our two galaxies has already begun.
The Crux
Motion is no stranger to our universe. The Milky Way and Andromeda indeed revolve around each other. You may broaden your inquiry to ask if the Local Group as a whole orbits something. And it does – the Local Group is a component of the Virgo Supercluster, which is in motion about far greater formations in the universe. After all, nothing is completely at rest.
