Well, not very much at any rate. It definitely does not explode or disintegrate. It does make some rather nice rings, but that's OK. I don't need (or expect) it to be perfectly stable - not exploding is all I ask.
This one is embedded in a dark matter halo. I don't have a script to convert the dark matter particles into a format I can display but I'll try and get one.
A number of failed attempts proceeded this one, even with the dark matter. I tried spherical clouds first, which worked well at low masses but not at high masses. With a spherical system the gas is supported by its temperature, which for a massive cloud has to be extremely high. That means an extremely high pressure, which I think was tending to blast things apart.
With a disc, the support comes from rotation much more than pressure. So the gas can be cool and is far less prone to expanding. I also used a lower mass of gas than in the previous runs. With a pure gas disc that would have meant the rotation speed would also have been lower, making it difficult to judge if it was really stable against rotation without doing a very long simulation. Anyway I need a higher rotation speed to match the observations.
With the dark matter, I don't need to worry about finding a sweet spot in terms of being hot enough to avoid collapse but not so hot it explodes. It's bound by the mass of the dark matter, not the gas - so if I make it hotter, it doesn't matter so much. A lot of instabilities caused by making it colder are also avoided - there's less differential rotation across the disc because the extra mass changes the rotation curve.
This isn't quite the disc I need - it needs a bit more dark matter, be a bit smaller, spin a bit faster, and the gas needs to be a bit hotter. But it's very close. With luck, by next week I should be able to chuck this into a galaxy cluster and watch the carnage (or lack thereof).
Nice! What kind of equipment are you using for crunching the numbers?
ReplyDeleteRhys Taylor You're attempting to model a stellar system accretion disc birth, right?
ReplyDeleteSakari Maaranen Thanks ! No special hardware here, just an ordinary desktop. 16 GB RAM, 3.2 GHz i7 processor. We have a computer cluster downstairs, but it's not needed for this. Simulations take ~2 hours to run, though that varies by a factor of a few.
ReplyDeletePaul McIntyre Nope, a galactic disc.
ReplyDeleteIt might be more interesting if you dyed the dark matter brighter. How about hot pink? Everybody knows divine fingers are pink as a piglet!
ReplyDeleteso the dark matter is outside? What about the center, the cluster is strange?
ReplyDeleteAndres Soolo Tim Stoev In fact since I don't have a script to plot the positions of the dark matter particles I have no idea what it's doing. It should be in a cloud of the same size of the disc. At least it is initially, but what it does as the simulation evolves I have no idea.
ReplyDeleteAs soon as I get the dark matter plotted, I'll be sure to make it bright luminous pink.
A new study is shedding pink light to dark matter. In a groundbreaking simulation experiment tomorrow, scientists are evolving a new model of dark matter involving what they describe as a 'bright luminous pink' element. To be continued...
ReplyDelete