# Tidal tails make dark matter-less galaxies **URL:** \ **Category:** Factual Questions\ **Created:** [March 9, 2022, 8:54pm UTC](https://boards.straightdope.com/t/tidal-tails-make-dark-matter-less-galaxies/960774 "2022-03-09T20:54:19Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [March 9, 2022, 8:54pm UTC](https://boards.straightdope.com/t/tidal-tails-make-dark-matter-less-galaxies/960774/1 "2022-03-09T20:54:19Z")
Here’s a blog by an astrophysicist which I think says that tidal tails caused by two galaxies making a near pass to each other will result in a dark matter-less satellite galaxy. > **[Mystery solved: how the Universe makes galaxies without dark matter](https://bigthink.com/starts-with-a-bang/galaxies-without-dark-matter-167405/)** > > Out of all the galaxies we know, only a few little ones are missing dark matter. At last, we finally understand why. However he isn’t as clear on this as could be (he doesn’t use the term _tidal tail_, for example), so could someone else read that and confirm that that’s what he’s saying. For those unfamiliar with the phenomenon: > **[Tidal tail](https://en.wikipedia.org/wiki/Tidal_tail)** > > Pages for logged out editors learn more > > A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. Tidal tails occur as a result of galactic tide forces between interacting galaxies. Examples of galaxies with tidal tails include the Tadpole Galaxy and the Mice Galaxies. Tidal forces can eject a significant amount of a galaxy's gas into the tail; within the Antennae Galaxies, for example, nearly half of the observed gaseous matter is fou... ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [March 10, 2022, 12:15am UTC](https://boards.straightdope.com/t/tidal-tails-make-dark-matter-less-galaxies/960774/2 "2022-03-10T00:15:58Z")
> [@dtilque](#): > > However he isn’t as clear on this as could be (he doesn’t use the term _tidal tail_ , for example), so could someone else read that and confirm that that’s what he’s saying. I see no reason to force the term “tidal tail” into the picture. In these simulations, tidal forces between interacting galaxies are indeed stripping the satellite galaxies of their gas and dark matter. Also, tidal forces between interacting galaxies can lead to distinctive tidal tails. But the latter doesn’t cause the former, _per se_. In other words, the statement “tidal tails…will result in a dark matter-less satellite galaxy” implies something a bit off about what causes what. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [March 10, 2022, 12:33am UTC](https://boards.straightdope.com/t/tidal-tails-make-dark-matter-less-galaxies/960774/3 "2022-03-10T00:33:12Z")
OK, I think I get it. The satellite galaxies that lose their dark matter were already around before the big galaxies got near each other. This confusion on my part may be because I’ve been wondering what eventually happens to tidal tails after the two galaxies merge. Do they fall back in to the combined galaxy, form a small galaxy of their own, or break up into small clusters of stars? Or maybe some combination of those? ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [March 10, 2022, 7:46pm UTC](https://boards.straightdope.com/t/tidal-tails-make-dark-matter-less-galaxies/960774/4 "2022-03-10T19:46:02Z")
Yeah, all of the above, depending on the dynamics of the specific collision and the timescale of interest. You can find some neat animations/simulations of galaxy collisions online that show some of the structural evolution, with tails whipping around and maybe spinning off or (often) coalescing back into the central galaxy.