Why Is The Andromeda Galaxy Moving Towards Us If The Universe Is Expanding?

Andromeda Galaxy is only 2.5 million light-years away from us. This means that the expansion of the Universe is carrying it away at only 60 km/s. As the strength of gravity between these galaxies and the invisible dark matter that surrounds them both is strong enough to overcome this expansive force. As a result, the Andromeda Galaxy is moving towards the Milky Way Galaxy at a speed of about 110 km/s. Andromeda Galaxy and the Milky Galaxy both belong to the Local Group. The expansion rate of the Universe is infinitesimally small at a local level. It’s only when you reach hundreds of millions of light-years does the expansion takes over from gravity. In short, the universe is expanding, not the Local Group of galaxies. It is a gravitationally bound structure.

Also Read: Kepler's Laws of Planetary Motion