Hello everyone and welcome back to my blog! This week is special because it is the final week of reading papers, so I can finally start working on my model. This week I read “Effects of Turbulence and Rotation on Protostar Formation as a Precursor of Massive Black Holes” by Van Borm et al. As usual, it is time for me to present what I learned in a way that you can hopefully understand.

Direct Collapse

In the early universe, there were huge, hot gas clouds that would later collapse into galaxies. There are multiple ways that they could’ve collapsed, but the way that matters to my model is the direct collapse scenario. The requirements for this scenario are that the gas cloud has a temperature greater than 10^4 K and that it is rotating relatively slow. The way that direct collapse works is that much of the matter in the gas cloud quickly falls directly towards the center. The slow rotation makes it easier to fall, and the high temperature basically forces matter into the center. This quick, large infall of matter allows a huge protostar (the things that evolve into stars) to build up in the center of the cloud. If the protostar keeps gaining mass at a rate of at least 0.14 solar masses per year, it gains enough mass for the core to collapse and form a quasistar.

Cooling

In order for all of that to happen, the gas cloud needs to both start hot and stay hot. There are a few things that need to happen so that heat doesn’t quickly escape the cloud. First, most of the gas in the cloud needs to be hot enough to stay as singular hydrogen atoms. If 2 hydrogens bond to each other, they cool much more efficiently. Second, the gas needs to be thick so that it absorbs radiation. In order for the gas to be thick enough to absorb the radiation that atomic hydrogen releases, it needs to have a density of at least 10^17 molecules (or atoms) per cm^3 (for comparison, the density of air at sea level is 2.7 * 10^19/cm^3). Collisions between H₂ and H atoms, other H₂ molecules, or He atoms have a high chance of releasing radiation, making thick gas even more important. Third, the gas in the cloud needs to have a very small amount of metals, as the radiation they produce can’t be absorbed by a 10^17/cm^3 cloud. In order for the gas to absorb nearly all radiation, it would need to have a density of 10^20/cm^3, which is very unrealistic for a gas cloud.

As I said earlier, this coming week I’ll finally start working on the model, so I’m very excited for that. With that being said, thank you for reading this week’s blog, and I hope you tune in next week as well!