Comment by seanw444
19 hours ago
So how do we know that these "dark matter objects" aren't actually just massive collections of normal matter that is dim enough and at such a far distance that it would appear (angular resolution-wise) to be invisible, but we can still detect the lensing?
> just massive collections of normal matter
Normal matter in the universe is mostly hydrogen, which should coalesce to form stars, which give off light. The lack of light compared to the estimated mass is precisely the paradox.
There are a few reasons. It would be visible when backlit. Gravitational lensing detection limits the size so it can't planets (MACHOs). The CMB shows that only sixth of matter interacts with other matter, the rest is only interacts gravitationally.