Detectability of Supermassive Dark Stars with the Roman Space Telescope

Saiyang Zhang; Cosmin Ilie; Katherine Freese

doi:10.3847/1538-4357/ad27ce

paper

Detectability of Supermassive Dark Stars with the Roman Space Telescope

arXiv:2306.11606 · doi:10.3847/1538-4357/ad27ce

Abstract

The first bright objects to form in the Universe at redshift $z \sim 10 - 20$ might have been Dark Stars, made primarily of hydrogen and helium but powered by dark matter. In this study, we investigate the detectability of Supermassive Dark Stars (SMDS) by the Roman Space Telescope. RST will be able to detect SMDSs at redshifts as high as $z ≃ 14$ . In cases with gravitational lensing factors of $μ \sim 100$ , RST will be able to find SMDS as small as $\sim 1 0^{4} M_{⊙}$ at $z \sim 12$ with $\sim 1 0^{6}$ s of exposure. To differentiate SMDS from early galaxies containing zero metallicity stars at similar redshifts, we compare their spectra, photometry in RST bands, color indexes and image morphology. With RST alone, the differentiation is possible only for limited cases: SMDS formed via "adiabatic contraction" (DM pulled into the star via gravity alone) with $M ≳ 1 0^{5} M_{⊙}$ and lensed by $μ ≳ 30$ have distinct photometric signatures from those of the first galaxies. For SMDSs formed via "dark matter capture," their spectra are degenerate to those of many galaxies with little to no nebular emission. Thus with RST alone, the only way to tell them apart from first galaxies would be via image morphology: i.e. point object (SMDSs) vs. extended object (sufficiently magnified galaxies). However, if the same objects are further examined by JWST spectroscopy, a "smoking gun" for detection of SMDS is the HeII $λ$ 1640 absorption line. While RST does not cover the wavelength band required to find this line (for $z_{emi} ≳ 10$ ), JWST does. Hence the two detectors can be used together in identifying SMDS. The confirmed detection of any SMDSs will provide evidence for a new type of star, powered by dark matter. Moreover, such massive stars can also be natural progenitors of the supermassive black holes powering the extremely bright quasars observed at $z ≳ 6$ .

arXiv comment49 pages, 24 figures

Detectability of Supermassive Dark Stars with the Roman Space Telescope

Abstract

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