In theory, dark matter is composed of particles that have mass (and can therefore produce gravitational effects that are noticeable if you have a bunch of them), but they do not interact with the particles that compose atoms via electromagnetic forces or via the "strong nuclear force" (the force that holds the nucleus of an atom together).
This means that dark matter is not like the "physical matter" that you're used to seeing. Dark matter doesn't absorb or emit light, so it doesn't block our view of some parts of the Milky Way. The stuff that blocks our view is basically "space dust", and that "space dust" is made of atoms, not dark matter.
According to the theories of dark matter, it can affect our view of other places in the universe, but only via "gravitational lensing". "Gravitational lensing" is where there are enough particles with lots of mass all together (like a galaxy) that they noticeably distort light as it goes by. There is compelling evidence for dark matter from observations of gravitational lensing effects near galaxies that do not have enough mass from their observable stars to account for the degree to which light is distorted as it goes past the galaxy--in other words, to produce that effect, some galaxies must have significant amounts of mass from particles which are not visible.
Why couldn't that extra mass be from "space dust"? Because there is an enormous amount of mass that we can detect via gravitational lensing, but which is not emitting or absorbing light. "Space dust" does not make up much mass for each galaxy compared to the stars and black holes. It's nowhere near the quantity required to produce the observed gravitational lensing effects.
Dark matter & gravitational lensing:
http://m.phys.org/news/2014-07-large-dark-peaks-gravitationa...
- This article notes that dark matter is estimated to comprise about 80% of the mass of the universe. If dark matter was made of visible particles, that would be like having four times as much visible material floating around in galaxies as the stars and black holes which comprise the galaxies, and somehow we don't see any of it.
This means that dark matter is not like the "physical matter" that you're used to seeing. Dark matter doesn't absorb or emit light, so it doesn't block our view of some parts of the Milky Way. The stuff that blocks our view is basically "space dust", and that "space dust" is made of atoms, not dark matter.
According to the theories of dark matter, it can affect our view of other places in the universe, but only via "gravitational lensing". "Gravitational lensing" is where there are enough particles with lots of mass all together (like a galaxy) that they noticeably distort light as it goes by. There is compelling evidence for dark matter from observations of gravitational lensing effects near galaxies that do not have enough mass from their observable stars to account for the degree to which light is distorted as it goes past the galaxy--in other words, to produce that effect, some galaxies must have significant amounts of mass from particles which are not visible.
Why couldn't that extra mass be from "space dust"? Because there is an enormous amount of mass that we can detect via gravitational lensing, but which is not emitting or absorbing light. "Space dust" does not make up much mass for each galaxy compared to the stars and black holes. It's nowhere near the quantity required to produce the observed gravitational lensing effects.
Related: Space dust: https://en.m.wikipedia.org/wiki/Cosmic_dust
Dark matter & gravitational lensing: http://m.phys.org/news/2014-07-large-dark-peaks-gravitationa... - This article notes that dark matter is estimated to comprise about 80% of the mass of the universe. If dark matter was made of visible particles, that would be like having four times as much visible material floating around in galaxies as the stars and black holes which comprise the galaxies, and somehow we don't see any of it.