How do we know dark matter is some mysterious form of matter and not just small distributed particles (gas or solid) that are beyond our ability to detect? Do we have proof of a specific, exotic, non-atomic matter?
Just on the back of an envelope: If we assume the percentages in my post above apply to an individual galaxy, then there has to be 5x as much dark matter mass as lit mass. There's no way you could have 5x as much gas and dust in a galaxy as stars, and not see it.
For comparison, the sun makes up about 99.8% of the Solar System mass (500x as much mass as all the planets, dust, etc. combined).
A bit of Googling tells me that the current estimate of its mass is in the order of 5-10 Earth masses--not nearly enough to explain dark matter.
https://www.wolframalpha.com/input/?i=mass+of+the+solar+syst...
So we might be here only because our solar system is surrounded by an unusual amount of nothing.
Consider that we can currently detect differences in luminosity small enough to tell whether an Earth-size planet is passing between us and the star. A 5x mass Oort cloud would be thousands of times more mass than that. It would have noticeable effect on luminosity.
And, while our sun has an Oort cloud, there are a lot of stars out there that probably don't--too small, too big, too hot, too young, too old, etc.
That leaves just 0.2% for all the planets, dust, Oort cloud, Kuiper belt, etc. So ... no.
Please don't just disagree when you don't know what you are talking about.
> That always confused me. We have an Oort cloud, whose members we cannot resolve very well/at all. Why do we assume only our star has such a thing? If all stars did, that isn't enough mass to explain dark matter?
No, that isn't enough mass to explain dark matter, since it's only 0.1% to 0.2% of the mass of the solar system.
The text I quoted was in complete agreement with what you and others have posted. I was pointing out that the questioner's point had already been answered.
Don't look at the current theory of dark matter (weakly interacting massive particles) as some hare-brained scheme that scientists thought up, instead look at it as the hard-fought victor of numerous observational challenges. Dark matter is the theory that survived. We tried explaining things a zillion other ways (gas clouds, compact objects, neutrinos) and those theories just didn't match the observations. There are also a few exceptional circumstances (such as the bullet cluster) that indicate very strongly that dark matter is something different than either gas clouds or stuff like stars and planets, because in the bullet cluster we can observe the gas and the stars and planets and the mass, and each of them are in different places because each of them follow different rules when it comes to interacting during a galactic cluster collision.
You mean like ether?
In reality, it's something we have no idea what it is, except that it's not visible and a big source of gravity.