4 ms·
If lensing is so hard to observe, why is lack of lensing considered enough to reject "dark matter==black holes"?
by nytgop77 6y ago
If lensing is so hard to observe, why is lack of lensing considered enough to reject "dark matter==black holes"?
- hannasanarion 6y agoBecause if the galactic halo was so full of black holes that it accounted for all the dark matter in the galaxy, then lensing would be extremely easy to detect. If the MACHO hypothesis was correct, there would be lensing everywhere you look because the whole galaxy is totally surrounded by enormous black holes. A lensing effect could be constantly seen viewing any object outside of the galaxy, because there's guaranteed to be a black hole in front of it. It would be difficult to get a good picture of any but the closest galaxies because of all the lensing artifacts from the black holes all over the place. Lensing around black holes is hard to detect precisely because black holes are so rare and don't frequently cross in front of very bright objects.