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bolverk / generalised_bondi

Semi analytic solutions to the generalised bondi problem
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Application to our galactic center #2

Open bolverk opened 7 years ago

bolverk commented 7 years ago

Almog wrote:

Re’em suggested we apply our model to our galactic centre, like Quataert 2004. Like in that paper, I got that the best fit for the density was obtained for \eta=0. This is very different from the power law index of the stellar density, which is between 1.4 and 2. The reason for the discrepancy might be due to the fact that wind emitting stars are more evenly distributed (see Rockefeller 2003).

Aleksey wrote:

There is an entire industry modeling the hot gas in the galactic center (a recent example here). Another good reference is Cuadra+2006, since they show how adding different different effects change the gas density from the Quataert model.

Overall, there is a lot of important physics which our model cannot capture (for example the angular momentum of the gas). I suggest we don't go deeply into this.

Angular momentum might be important at small radii, but its effect diminishes as the radius increases. In addition, collisions between winds mitigate this problem. What other physical effects do they consider?

I agree that we shouldn't go too deep, but we should address this issue to some extent.

alekseygenerozov commented 7 years ago

They explore a few different effects: (i) Discreteness of stellar sources (ii) Angular momentum of the gas (due to motions of the stars especially when they are in a disk -- as is the case for the massive stars in the galactic center). (iii) A range of stellar wind velocities. Overall they find fairly substantial differences with Quataert especially with their stellar disk model.

There were some works which tried to include more sophisticated microphysics like conductivity and a 2-temperature plasma (see here, though I think this is somewhat dubious (for example conductivity may be suppressed by magnetic fields).

bolverk commented 7 years ago

Overall they find fairly substantial differences with Quataert especially with their stellar disk model.

What are the differences? are they consistent with observations?

alekseygenerozov commented 7 years ago

The Cuadra paper finds a shallower rise in the density on small scales than Quataert for the same value of eta (For example see their Fig. 5. In general, they take eta=2).

To 0th order, yes I think that their density profile is consistent with observations. Of course to really compare to observations you have to create a simulated x-ray image and compare to the galactic center. They do not attempt to do such a detailed comparison.

One example of such a detailed comparison is here, though they don't directly model injection of stellar winds, and they mostly focus on the region inside of rb~0.1 pc. They find that including angular momentum of the gas is necessary to get a good match to x-ray observations on small scales...