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For the last point. Where do we get our confidence in the (light) mass estimation of a galaxy? Couldn't we be off by a factor of 10?
by rocqua 6y ago
For the last point. Where do we get our confidence in the (light) mass estimation of a galaxy? Couldn't we be off by a factor of 10?
- knzhou 6y agoMostly the confidence comes from half a century of trying to find such "extra" visible mass! There's a long history of people looking for extra dust or gas or compact objects using a tremendous variety of clever techniques, and yet the deficit has remained. At this point, if you believe that there indeed is extra mass around, it kind of has to be dark matter by definition because it's been so damn hard to see.
- NohatCoder 6y agoThe question is how the f do we know the mass of a galaxy in the first place? We can't have the discrepancy until we have two distinct methods of measuring the mass of a galaxy.