Bad Astronomy (@BadAstonomer): When Galaxies Strip For Each Other
Polar ring galaxies are, as you might expect from seeing them, rather odd.
The outer ring in Hoag’s Object (bottom picture) has lots of young, hot stars, and the gas and dust needed to keep forming them, while the center, looking very yellow, is full of older stars and no star formation.
NCG 660 has a similar ring, but it is out of kilter (Hoag’s is perpendicular to the central core) and warped.
So, Phil tells us he read up on it and found that galaxies in near-passes (instead of collisions) can end up pulling the gas and dust out of each other, and into these rings. And, since they are moving slowly, the gravitational tidal forces start pulling the gas and dust into different places in the galaxy, even the center. So, while Hoag’s Object has no star formation in the center, NGC 660 has a bit of star formation both in the ring and in the center.
Phil learns something new and so, then, do we all. (Because, hey, let’s face it, he’s a professional astronomer and can understand these things quite a bit more easily than I can, and then he explains pretty well, too.)