What would happen if dark matter disappeared ?

[Rhysy]

This may be of interest. It's a simulation a friend ran for me (because I asked nicely) showing what would happen to a run-of-the-mill spiral galaxy if it suddenly and magically lost all of its dark matter. I've always wanted to see this, because I've been telling people for years that without dark matter galaxies would fly apart. Turns out (reassuringly) that's exactly what they do. Though it's a bit more complicated than that, because dark matter is only really important in the outer parts of the disc. The inner parts don't really notice.

Click to play embedded YouTube video.

I wrote a more detailed article about this on my blog : http://astrorhysy.blogspot.com/2013/05/ ... -them.html

[Markus Schwarz]

Nice work Rhys and Rory!

Is there a reason why the central bulge starts to move to the "upper right"? Naively, I would imagine that the center of gravity stays at the center.

[Rhysy]

Thanks !

You're right, it should stay central. I think it's because of small numerical errors which are increased because the program was never designed to have 90% of the mass suddenly removed. Apparently the first run generated 10GB of error messages, which is clearly not a sign of a happy program. It also resulted in the central part of the galaxy moving quite neatly along the line y=x. This version is a lot better, but not perfect.

Rhys

[MargaritaMc]

Very interesting piece of work, Rhysy - thanks a lot.
Just noting that you are the "rhysy" who produced that helpful galaxy size comparison chart which was posted in April are you not?

http://asterisk.apod.com/viewtopic.php? ... 04#p196682
Margarita

[Beyond]

Very interesting piece of work, Rhysy - thanks a lot.
Just noting that you are the "rhysy" who produced that helpful galaxy size comparison chart which was posted in April are you not?

http://asterisk.apod.com/viewtopic.php? ... 04#p196682
Margarita

I just checked the two links in your viewtopic Margarita, and they're now blocked because of Zoomit.com code violations.

[MargaritaMc]

Very interesting piece of work, Rhysy - thanks a lot.
Just noting that you are the "rhysy" who produced that helpful galaxy size comparison chart which was posted in April are you not?

http://asterisk.apod.com/viewtopic.php? ... 04#p196682
Margarita

I just checked the two links in your viewtopic Margarita, and they're now blocked because of Zoomit.com code violations.

So they are!
The original is at:

http://astrorhysy.blogspot.com.es/2013/ ... chart.html

I'll put a comment on the blog that the zoomit versions are defunct.
Margarita

[MargaritaMc]

PS. I've just discovered a video version of the zoomable galaxy size comparison in Video submissions.

http://asterisk.apod.com/viewtopic.php? ... 50#p197344

[Rhysy]

Yes, I am he.

I don't know why the images should be blocked for "code of conduct" violations... maybe it's because I removed the original images (I don't know how zoomit works exactly, perhaps they require the originals to be accessible ?). Anyway the links in the original blog post do work. I edited them because someone pointed out that I'd got the size of a light year wrong by a factor of 1000.

[MargaritaMc]

Yes, I am he.

I don't know why the images should be blocked for "code of conduct" violations... maybe it's because I removed the original images (I don't know how zoomit works exactly, perhaps they require the originals to be accessible ?). Anyway the links in the original blog post do work. I edited them because someone pointed out that I'd got the size of a light year wrong by a factor of 1000.

Good to have you here!
But quite disappointed in the explanation about the 'code of conduct violations '! I thought that at least you would have run off with the MD's cat!

Do you think you could put a post on the original thread (follow the link above on my or Beyond's post) to say where the zoomable image is now available?

Margarita