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Astronomers keep trying to measure the mass of the Milky Way and they keep coming up with different numbers. But it’s not that they’re bad at math. Measuring the mass of something as enormous as the Milky Way is confounding. Plus, we’re embedded in it; it takes some very clever maneuvering to constrain its mass.
The Milky Way’s mass is a fundamental scientific question that astronomers have been trying to answer for decades. The problem is, even astronomers’ best estimates vary wildly. The difficulty arises not from measuring the mass of the stars themselves. It comes from the challenge of measuring dark matter.
First - Matter - Something
First of all, dark matter is hypothetical. We don’t really know what it is. But we know it’s there, or rather we know something’s there.
The things we can see and interact with are made of what’s called ‘baryonic matter.’ It’s made of atoms and it’s all the stuff we’re familiar with: Our bodies, the planets, stars, Kim Jong-un’s eyeglasses, etc. But baryonic matter only makes up about 10-15% of matter in the universe.
Matter - % - Matter - Universe - Matter
We think that dark matter makes up about 85-90% of the matter in the universe. It’s distinct from regular matter because it doesn’t interact with light and we can’t see it. That’s why it’s called dark matter.
But we know it’s there because galaxies behave as if they have way more mass than we can see. The hint that it’s there is in the gravity. Galaxies must have more mass, and hence more gravity, than we can see in their regular matter, or they would just fly apart. Their mass and gravity hold them together.
Version - Things - Way - Lot - Mass
The short version is that things just couldn’t be the way they are unless there was a lot more mass than we can measure.
“We just can’t detect dark matter directly.”
“We just can’t detect dark...
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A pox on both their houses!