Video lecture discussing the evidence for Dark Matter in galaxies. Explains the concept of rotation curves and how it leads to evidence of non-luminous material in galaxies.
Excellent description. I am helping some people with studying for Intro Astronomy exam, and this video is the most concise and clear I've found without any bells and whistles.
My thoughts : 🤔 Galaxy rotation curve is may be little bit due to distribution of gravitational time dilation in space from galactic center to us and from us to outer side of galaxy for our Galaxy and same for all galaxy's Because mass density in the center of galaxy is higher then middle ( where our earth is ) so time runs slower in center then middle , so stars only appears that it is moving slower relative to us . And for why we see outer stars of galaxy orbiting faster then it should be it is because time runs faster in less dense area of outer side of galaxy so that appears that they are moving faster relative to us . If it's wrong then why ???
There are several hypotheses to explain the rotation curves, including a modified form of gravitational theory. So far, there isn't a definitive answer, but the particle (Dark Matter) hypothesis has the most plausible evidence for it, and it also is consistent with more observations and physical theory than any of the MONDs (Modified Newtonian Dynamics) models out there. Always good to keep thinking :-)
Came here for dark matter, got totally sidetracked in trying to understand how the spiral structures of any galaxy work (upon realizing a few seconds in that, of course, the galaxy does not rotate as if it were a solid pinwheel spinning).
so a galaxy is actually not nearly as extreme as a vinyl record, because in that case the speed would constantly go up with distance. instead it seems to remain roughly the same. that's strange. are there measurements of objects far out, near the edge of the halo where the orbital speed starts to behave like in the solar system? the curves seem to suggest that it never goes down.
In my opinion we cannot compare the motion of stars in a galaxy with billion stars to the motion of planets in the solar system, thus can hardly accept that this equivalence justifies the existence of DM which, in fact, after 30 years or so has never been discovered.
But even the star mass isn't all in the centre, most if it is there and it gradually falls off towards the edges of the visible galaxy, shouldn't this atleast a little contribute to the graph being straight?
Umm, we just figured out that there are many more visible stars in our own galaxy that we had no idea about previously. I think we are mostly blind, and this is the true darkness.
I agree with the comment left a year ago: this is an EXCELLENT and very clear piece of teaching.
Excellent description. I am helping some people with studying for Intro Astronomy exam, and this video is the most concise and clear I've found without any bells and whistles.
My thoughts : 🤔
Galaxy rotation curve is may be little bit due to distribution of gravitational time dilation in space from galactic center to us and from us to outer side of galaxy for our Galaxy and same for all galaxy's
Because mass density in the center of galaxy is higher then middle ( where our earth is ) so time runs slower in center then middle , so stars only appears that it is moving slower relative to us . And for why we see outer stars of galaxy orbiting faster then it should be it is because time runs faster in less dense area of outer side of galaxy so that appears that they are moving faster relative to us .
If it's wrong then why ???
There are several hypotheses to explain the rotation curves, including a modified form of gravitational theory. So far, there isn't a definitive answer, but the particle (Dark Matter) hypothesis has the most plausible evidence for it, and it also is consistent with more observations and physical theory than any of the MONDs (Modified Newtonian Dynamics) models out there. Always good to keep thinking :-)
Excellent video mate, thank you very much.
Came here for dark matter, got totally sidetracked in trying to understand how the spiral structures of any galaxy work (upon realizing a few seconds in that, of course, the galaxy does not rotate as if it were a solid pinwheel spinning).
Thank you so much for this video! I understood everything
so a galaxy is actually not nearly as extreme as a vinyl record, because in that case the speed would constantly go up with distance. instead it seems to remain roughly the same. that's strange. are there measurements of objects far out, near the edge of the halo where the orbital speed starts to behave like in the solar system? the curves seem to suggest that it never goes down.
In my opinion we cannot compare the motion of stars in a galaxy with billion stars to the motion of planets in the solar system, thus can hardly accept that this equivalence justifies the existence of DM which, in fact, after 30 years or so has never been discovered.
But even the star mass isn't all in the centre, most if it is there and it gradually falls off towards the edges of the visible galaxy, shouldn't this atleast a little contribute to the graph being straight?
My bet is that there is no dark matter just bad interpretation of gravitational forces.
Umm, we just figured out that there are many more visible stars in our own galaxy that we had no idea about previously. I think we are mostly blind, and this is the true darkness.