The bright galaxies that the JWST unexpectedly discovered shortly after the Big Bang may not be powered by hydrogen mergers, as stars are today, but by concentrations of dark matter, physicists have suggested. These “dark stars” are said to have masses a million times that of the Sun. Don’t let the name fool you though – astronomers believe such stars would also be more than a billion times as bright as the Sun, which explains why we can see them from such great distances.
Since we don’t know what dark matter is made of, any reference to its ability to power light sources is highly speculative. Still, some of the very early galaxies discovered by JWST are difficult to explain, opening up space for ideas previously thought to be edge galaxies.
In a new paperR, Three physicists from Colgate University show how their idea of ”dark stars” could explain some of the anomalies in the JWST observations.
The fact that light is not infinitely fast means that in order to see anything you have to look back in time. The JWST has seen galaxies more distant than anything before, and therefore looks further back in time, almost to the Big Bang itself. These earliest galaxies appear to be more evolved than conventional physics has predicted in the limited time available would consider possible. Most physicists believe that this paradox can be solved with relatively minor changes to existing models of the Universe, but some are exploring more radical options.
The researchers suspect that the first stars formed mostly from hydrogen and helium, like those in our own galaxy, but that concentrations of dark matter provided a source of energy for their heating, which happened faster than fusion took off. So-called galaxies are rather individual stars that achieve galactic brightness in this way. At that distance, they argue, the JWST lacks the angular resolution to determine whether it’s seeing a point source or a more widespread galaxy.
According to the authors, dark stars are so large that if they were replaced, their surface would be outside of Saturn’s orbit. Even given their enormous mass, fusion could not be sustained over such a large area. Instead, dark matter particles annihilate themselves, releasing enough energy to heat the surface to 10,000K (similar to Sirius), producing a staggering amount of light.
Such an energy release cannot be sustained for long. The authors believe that when dark stars run out of dark matter to fuel themselves, they collapse into black holes, providing the seeds for the supermassive black holes (SMBH) found at the core of galaxies. The presence of such evolved SMBHs powering quasars in the early Universe is another problem that physicists struggle to explain.
Although dark stars could solve some of the cosmological problems brought to light by the JWST, we do not know if dark matter particles are their own antiparticles and therefore can annihilate as the authors suggest. Would stars of this kind be stable even if they could? Were hydrogen and helium sufficiently concentrated in the early Universe to produce objects of the magnitude this proposal calls for? Modeling may suggest that the ideas are plausible, but we don’t yet have evidence that this is real.
In addition, the work acknowledges that one of the four early universe objects whose spectra passed an initial fitness test may not fit the Dark Star model. If this object, JADES-GS-z10-0, is anything more conventional than a Dark Star, critics might remark, the other three might be, too.
However, the paper is more than speculative. The authors suggest that if the other three objects in question are Dark Stars, their spectra should show prominent helium lines, particularly an absorption line at 1640 Angstroms, where a galaxy of ordinary stars would have emission lines. So far, the JWST has not investigated the three in enough detail to resolve the matter. The authors want to change that.
The paper was published in Proceedings of the National Academies of Science.