Stars in the early universe and stellar processes

[snorkack]

What does a star passing through Hayashi forbidden zone look like?
There are 2 ways for a star to exist in Hayashi forbidden zone: either it is hydrostatically supported by degeneracy pressure, in which case it is small and of low luminosity, or else it is rapidly contracting.
And a star contracting through Hayashi forbidden zone should be big and bright (in near-infrared).
Since a lot of brown dwarfs are seen in near-IR, despite being small and dim, how about big and bright protostars in Hayashi forbidden zone?

 

[Ken G]

What does a star passing through Hayashi forbidden zone look like?

It isn't called a star at all, that's star formation. And as I said, one needs a different approach to answer that question-- rather than the approach we take for stars, which is asking "what set of simplifiying idealizations can help us understand the basic structure of stars in such a way that time becomes a kind of external driving parameter", one needs to follow the time evolution explicitly from stage to stage. That is much more difficult, because you cannot know what is happening in any stage without first knowing the situation in the previous stage.

There are 2 ways for a star to exist in Hayashi forbidden zone: either it is hydrostatically supported by degeneracy pressure, in which case it is small and of low luminosity, or else it is rapidly contracting.

As I said above, the Hayashi limit does not apply for degeneracy, it applies for ideal gases. Including degeneracy allows a continuous transition from star models to brown dwarf models to planet models, all the way down to the blueprints for your house. But the topic of the thread was defined early on.

Since a lot of brown dwarfs are seen in near-IR, despite being small and dim, how about big and bright protostars in Hayashi forbidden zone?

As I said, brown dwarfs can have long-lived phases in that region, because they can be in a stable hydrostatic equilibrium. Stars like the Sun, which are not degenerate until they become white dwarfs, cannot.