Earendel and HD1; identifying population 3 stars and galaxies

Question

Will JWST be able to tell if Earendel, a 12.9 billion year old star, is a population 3 star? Or do we already know from the current Hubble observations that Earendel is a population 3 star?

I've read that population 3 stars are the previously never observed first stars in the universe which would have formed from only primordial hydrogen and helium and a little lithium, and would lack all other heavier elements, and which might have other unusual properties.

Also, will JWST be able to tell if galaxy HD1, a recently observed 13.5 billion year old galaxy consists of population 3 stars? EarthSky Most distant galaxy yet discovered says:

Scientists estimate that HD1 is forming more than 100 stars every single year. This rate is at least 10 times higher than a normal starburst galaxy. This is one of the reasons they think the galaxy is not forming “normal” stars.

If 100 stars are forming every year, might there also be 100 supernova every year as well, and would they be visible to JWST, or other observatories? What might we learn about those earliest stars and galaxies?

Also, if this is a mostly population 3 star galaxy then most of the supernova could be incredibly bright pair instability supernova. Might the brightness of HD1 be explained by these much brighter and longer lasting pair supernova? HD1 could in effect always be shining by light mostly generated from dozens of Pair-instability-supernova.

Answer 1

I will attempt to provide an answer to the first question (or pair of related questions):

Will JWST be able to tell if Earendel, a 12.9 billion year old star, is a population 3 star? Or do we already know from the current Hubble observations that Earendel is a population 3 star?

The short answer is "maybe". According to Welch et al. (2022), which presents an analysis of multi-band JWST imaging of Earendel, spectroscopy with NIRspec -- which would be the best way to get a handle on the nature of Earendel -- is currently "expected" for December, 2022.

Schauer et al. (2022) discuss the possibility that Earendel could be, from a statistical point of view, a Pop III star. They note that

There is a significant chance that Earendel is a Pop III star if it is indeed a single star of high mass. Given that the magnification is quite uncertain, determining the location of Earendel in the Hertzsprung–Russell diagram is only possible using spectroscopy. NIRSpec on board JWST has the required sensitivity to detect, e.g., mass-sensitive non-LTE He ii emission features in Earendel's spectrum (Bromm et al. 2001; Nakajima & Maiolino 2022), expected to have equivalent widths of ≳100 Å. If, on the other hand, Earendel is a low-number multiple, the most massive member star will dominate and there will remain some uncertainty, although it is still likely that a Pop III origin can be confirmed or ruled out spectroscopically.

Current Hubble observations do not tell us whether it is Pop III; even the recent JWST imaging observations by Welch et al. can't tell us that, either. (The latter do provide good evidence that it is probably a star -- or maybe a binary star -- rather than a cluster.)