How fast is our galaxy moving through space? Is the movement due to the expansion of the universe?
Our Milky Way galaxy is huge, massive, and most importantly, is in motion. All the stars, planets, gas clouds, dust grains, black holes, dark matter and more move around inside of it, contributing to and affected by its net gravity. But is the galaxy itself stationary? Most certainly not! In space, you see, there’s the gravitation of every other massive (and energetic) object to contend with, and gravitation causes any masses around to accelerate. Give our Universe enough time — and we’ve had some 13.8 billion years of that — and everything will move, drift and flow in the direction of the greatest gravitational attraction. That’s how we go from a mostly uniform Universe to a clumpy, clustered, galaxy-rich Universe in relatively short order. It means our Milky Way is being pulled by all the other galaxies, groups and clusters in our vicinity. It means that the closest, most massive objects around are going to be the ones that dominate our motion. And it means that not only our galaxy but all the nearby galaxies are going to experience a “bulk flow” due to this gravitational force. Recently, this has been mapped to the greatest precision ever, and we’re continually coming closer to understanding our cosmic motion through space.
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