An article published in the journal “Proceedings of the National Academy of Sciences” reports the discovery of candidate supermassive dark stars observed by the James Webb Space Telescope (Image NASA/ESA). Cosmin Ilie, Jillian Paulin, and Katherine Freese argue that three of what were considered primordial galaxies have characteristics of a type of object that so far was only hypothesized. According to the model proposed in 2007, supermassive dark stars have a large dark matter component that powers them instead of nuclear fusion. These strange objects could reach masses up to ten million times the Sun’s and a brightness up to ten billion times the Sun’s, which could lead to mistaking them for primordial galaxies.
The study of what were considered primordial galaxies within the JWST Advanced Deep Extragalactic Survey (JADES) program demonstrated the James Webb Space Telescope’s performance in observations of the early universe. One possibility was that they even hosted stars from the first generation that existed in the universe, but now a new analysis of those observations offers an alternative interpretation of the nature of three of those objects.
In 2007, Katherine Freese and two other colleagues, Douglas Spolyar and Paolo Gondolo, proposed a mechanism by which certain conditions in the early universe could lead to the formation of supermassive dark stars. In simple words, according to this hypothesis, at the center of the first protogalaxies, there were clusters of dark matter together with clouds of hydrogen and helium. In this situation, the cooling of the gas could have caused a collapse that included the dark matter due to the gravitational interaction. Due to its high density, dark matter may have begun to annihilate itself preventing the collapse from forming a normal star powered by stellar fusion. Common matter and dark matter may have continued to coalesce in an object with a mass up to ten million times the Sun’s.
The expression dark star is due to the significant presence of dark matter but the annihilation of the particles that power this type of object could generate a very bright light, up to ten billion times the Sun’s. Such an object could be mistaken for a primordial galaxy.
The objects cataloged as JADES-GS-z13-0, JADES-GS-z12-0, and JADES-GS-z11-0 and classified as galaxies were considered supermassive dark star candidates in this new study. These objects must show in spectroscopic measurements a helium absorption line called He II at 1640 ångström. The identified candidates show that line, which shouldn’t be present in primordial galaxies.
Verifying the existence of supermassive dark stars is difficult because the model that describes them indicates that only in the early universe were all the conditions for their existence to exist. In particular, metallicity, which means the presence of elements heavier than hydrogen and helium, increased with the passing generations of common stars that generated heavy elements that were scattered by supernovae in the gas clouds.
Confirming the existence of supermassive dark stars would solve one of the problems caused by recent observations by the James Webb Space Telescope, which found too many of what appear to be massive galaxies in the early universe compared to predictions from current cosmological models. If we were dealing at least in part with supermassive dark stars and not with galaxies, the models could be correct, or in any case, they could only need some refinement and not major revisions.
The Nancy Grace Roman Space Telescope, scheduled to launch in 2027, could help find new supermassive dark star candidates. Katherine Freese and Cosmin Ilie, together with their colleague Saiyang Zhang, wrote an article on this topic which also concerns the problem of how these objects look like galaxies. The ALMA radio telescope could also find candidates by detecting other spectral lines at wavelengths longer than He II. While waiting for new follow-up studies of JADES-GS-z13-0, JADES-GS-z12-0, and JADES-GS-z11-0, the hunt for other candidates continues for the interest of astronomers and physicists.
