# On the Detection of Supermassive Primordial Stars. II. Blue Supergiants

## TL;DR

This paper models the spectra and brightness of hot, blue supermassive primordial stars, suggesting they could be detected by upcoming telescopes like JWST, Euclid, and WFIRST at redshifts up to 10-12.

## Contribution

It provides the first detailed spectral and photometric predictions for blue supermassive primordial stars, highlighting their potential observability.

## Key findings

- JWST can detect these stars up to z ~ 10-12
- Euclid and WFIRST could detect them with gravitational lensing
- Blue supermassive stars are brighter and hotter than previously modeled red hypergiants

## Abstract

Supermassive primordial stars in hot, atomically-cooling haloes at $z \sim$ 15 - 20 may have given birth to the first quasars in the universe. Most simulations of these rapidly accreting stars suggest that they are red, cool hypergiants, but more recent models indicate that some may have been bluer and hotter, with surface temperatures of 20,000 - 40,000 K. These stars have spectral features that are quite distinct from those of cooler stars and may have different detection limits in the near infrared (NIR) today. Here, we present spectra and AB magnitudes for hot, blue supermassive primordial stars calculated with the TLUSTY and CLOUDY codes. We find that photometric detections of these stars by the James Webb Space Telescope (JWST) will be limited to $z \lesssim$ 10 - 12, lower redshifts than those at which red stars can be found, because of quenching by their accretion envelopes. With moderate gravitational lensing, Euclid and the Wide-Field Infrared Space Telescope (WFIRST) could detect blue supermassive stars out to similar redshifts in wide-field surveys.