Oops, I did it again

Last year there was the simulation where the dark matter content of a galaxy was suddenly and brutally removed. Consequently, half of it exploded.

This one is similar but less intentional. I'm trying to get the gas to have self-gravity, so we don't have to simulate it with a fixed, analytic potential (which is unrealistic except in the case that the disc is stable). Got that working, but I had problems compiling the code with the analytic gravity as well, so I just commented it out. Et voila...

In last year's simulation we not only had dark matter and gas but also stars. In centre of the galaxy, the stellar mass dominates. Problem is in this simulation, there aren't any stars, and the mass of the gas is negligible - not nearly enough to hold it together. So this time it's not just the inner regions but the entire gas disc which flies apart. Since the boundary conditions are periodic (anything that hits the edge re-appears on the opposite side), what you get is an expanding gas disc that collides with itself. And behold, all hell breaks loose.

RESCUE ALL THE HYDROGEN OVERPASSES !

RESCUE ALL THE HYDROGEN OVERPASSES !

Multiple Google translates, methinks. Choice highlights :

"Using a William E. Gordon Telescope, astronomers rescued a overpass of atomic hydrogen gas 2.6 million light years prolonged between galaxies 500 million light years away."
SAVE THE HYDROGEN ! SIGN THE PETITION !

"...Arecibo Observatory, a radio astronomy trickery of a US National Science Foundation..."
No comment.

" “Student impasse is really critical to us." "
God forbid we should actually teach them anything useful.

via Robert Minchin
http://techknowbutler.net/astronomers-discover-a-bridge-of-atomic-hydrogen-gas-2-6-million-light-years-long

Hydrogen clouds in the Milky Way

I just discovered the VLA Galactic Plane Survey - oodles of high resolution hydrogen data to play with. I can probably get this looking nicer with some tweaking.

I don't need no stinkin' gravity

Another FLASH simulation gone wrong. More adventures with ram pressure stripping. This time I moved the gas disc inside the computational domain so that the stripped wake would be longer. I also set the density of the initial medium and the inflowing wind to the same value. What I forgot to do was move the gravity... these tests use a fixed analytic potential for the dark matter [I don't remember if we used self-gravity for the gas; we probably did but the dark matter is hugely mass dominant]. So now the disc finds itself not only being blasted by a 1,000 km/s wind but also without having any gravity holding it in place. Oops.

And I rendered it rotating as well this time, just for good measure.

Introducing FRELLED

Why your ancestors not being eaten by a lion makes you well-suited to detecting extragalactic hydrogen, and the amount of work that goes into a few paragraphs in a publication. Also, why Blender is really really cool.


Placeholder post intended to be replaced with a better summary.

Giant gas streams in the mass media

More detailed article about the giant gas stream now on Vice. Press releases are cool.
http://motherboard.vice.com/read/colliding-galaxies-left-a-stream-of-gas-26-million-light-years-long

Galaxy Simulations As Abstract Art

Not another FLASH simulation today (perhaps tomorrow). This one's a particle-based sim of a star-forming gas blob being hit by a hot wind. Instead of animating it, every frame from the simulation is shown at once, so it shows the particle trajectories.

Gas is white, stars are the very bright hard lines, and dark matter is in green because green is nice.

A cosmic jellyfish

Simulation I set running before I went on holiday. This one has a much higher density surrounding medium than the last one did, so the effects are much more dramatic. As with the last one, it's an otherwise stable cold, dense gas disc face-on to a 1,000 km/s wind of hot, low density gas.

Unfortunately I forgot to change the density of the wind. So, although the surrounding medium is initially much denser, as intended, it gets quickly replaced by a much lower density medium.

Interestingly, even after the medium is replaced with the uniform low-density gas, the cold gas removal seems to happen in pulses. That wasn't what I was expecting at all.