Open tassos25 opened 2 days ago
The integration for BH spin alignment due to accretion is too slow. In my NSHB paper, I did a simplified calculation. I assumes the BH accretes the angular momentum of a chunk of mass at the ISCO only at the direction of the orbital plane (Y axis), and the angular momentum at X axis remains unchanged. Then, we have a new spin magnitude and a new direction. Issues: I used IF, so I assumed all the mass is thrown only once. This could potentially induce a final spin greater than one. The condition at ISCO changed step by step, and we didn't consider this.
An additional complication is that the specific AM of teh ISCO, does depend also on the angle between the plane of the assumed accretion disk and the BH spin, which is also evolving. In Fragos et al. (2010), we followed the evolution self-consistently, but there is a root finder involved in the solution, that slows down things. I had dug out the IDL scripts i used to do the calculation, which Zepei had translated to python.
This is a subtle but important process that I do not think any other BPS does correctly. It becomes especially important when looking at the misalignment angles of BH spins. It's one of these things that people assume it is doen correctly, but in most cases it is not. I suggest that we work on a better implementation before the v2 code release.
In teh v2 paper, section 5.4, we say:
In Fragos et al. 2010, we had performed the necessary integration in order to estimate the spin alignment. We should implement the same the sam thing in a computationally efficient way in POSYDON as well.
@ZepeiX had already experimented with some implementations but found it to be too slow. @ZepeiX can you comment?