[Diogo_Afonso_Leitao (OP)]

Hello!

My name is Diogo and I'm 13 years old. Currently I am making a video about dark matter! I am not sure if I can say correctly that ALL galaxies have dark matter halos around them so I would like to be sure of the information. After all, I don't want to spread misinformation

Thank you!

[chris]

This is a very good question, and a hard one to answer. In fact, I have asked more broadly for some input here...

Who can help?

[evan_au]

There are claims from NASA that in the Bullet Cluster, a high-velocity impact of Matter (which interacts strongly) has separated from the expected accompanying Dark Matter (which interacts weakly, if at all, with Matter or Dark Matter).

They used the technique of gravitational lensing to detect the invisible Dark Matter by its gravitational impact on light from more distant galaxies.
See: http://chandra.harvard.edu/press/06_releases/press_082106.html

There have been some contentious claims that certain galaxies show no signs of Dark Matter, for example:
https://www.newscientist.com/article/dn13280-galaxy-without-dark-matter-puzzles-astronomers/

But for now, most cosmologists think that the universe could only get the way we see it today if there is far more Dark Matter in the universe than the Matter we can see.

Most astronomers think that most galaxies show signs of a Dark Matter halo through internal evidence (rotation curves) or external evidence (gravitational lensing), among others.

It's just that we don't know what Dark Matter is, as yet - but that won't stop scientists dreaming up theories (that might win them a Nobel Prize, someday).