Can JWST see galaxies made of primordial stars?

All stars are composed of principally hydrogen and helium, however most stars even have measurable quantities of heavier components, which astronomers lump into the class of “metals.” Our sun has extra metals than most stars as a result of the nebula from which it shaped was the remnant particles of earlier stars. These have been in flip kids of even earlier stars, and so forth.

Usually, every new era of stars has a bit extra metallic than the final. The very first stars, these born from the primordial hydrogen and helium of the cosmos, had nearly no metallic in them. We have by no means seen one in every of these primordial stars, however with the facility of the Webb and a little bit of luck, we would catch a glimpse of them quickly.

One strategy to decide the quantity of metallic a star has is by evaluating the ratio of iron in its environment in comparison with helium, referred to as [Fe/He]. This metallicity quantity is normally expressed on a logarithmic scale, the place the sun’s metallicity is about to zero. Stars are then set into populations primarily based on this quantity. Any star with a metallicity of no less than -1 (that means it has no less than 10% of that of the sun) is a Inhabitants I star. Stars with decrease metallicity are Inhabitants II stars, and the very first stars with no observable metals can be Inhabitants III stars.

Within the Milky Way, Inhabitants I stars are sometimes discovered throughout the galactic plane and spiral arms, whereas Inhabitants II stars are principally in a extra diffuse halo of stars surrounding the galaxy. This is smart, since stars type throughout the fuel and dust of spiral arms, and might drift away from the galactic aircraft as they age. Aside from the truth that Inhabitants II stars are normally billions of years older than the sun, they’re broadly much like youthful stars.

The primary era of stars is assumed to have been very totally different. The extra metallic a star has the extra dense it may be. A star such because the sun is extra compact than a Inhabitants III star, and due to this fact does not want as a lot mass to shine so brightly. Because the first stars have been made solely of hydrogen and helium, we predict they have been massive stars that lived brief however very luminous lives. They possible shaped through the first few hundred million years of the universe, and died inside a number of tens of million years or much less. The one approach we are able to see their mild is by peering into the deepest reaches of space. Even the brightest galaxy of Inhabitants III stars can be very dim as seen from Earth. However are they too dim for the almighty Webb to watch?

That is the query this current examine, accessible on the preprint server arXiv, tried to reply. The group simulated each the depth and spectrum of first-generation stars to find out how they could seem inside an early galaxy, then in contrast this to the aptitude of the Webb Area Telescope. They discovered that if Webb had a direct, unobstructed view of a brilliant primordial galaxy, it will nonetheless be too dim for Webb to see. But when a very massive primordial galaxy occurs to be positioned behind a big nearer galaxy, gravitational lensing might amplify and brighten the distant galaxy’s mild to a degree the place Webb might detect it.

In different phrases, we’re on the irritating fringe of with the ability to detect first-generation stars. If issues are lined up simply so, and we are able to separate the spectra of the first-generation galaxy from the nearer galaxy, then we’ve got an opportunity. Which will sound disappointing, however astronomers are expert and intelligent, so there’s purpose to hope that in time we’ll see mild from the grandmothers of all stars.