What is the Supermassive Dark Star hypothesis, and what supports a recent claim of their existence?
Article by: Keisha Kwok, on 28 August 2023, at 01:42 pm PDT
The idea of a dark matter star existing in the early universe was initially proposed by a group of researchers in 2008. Unlike regular stars that derive their energy from nuclear fusion of hydrogen into helium, dark matter stars are powered through a process called Dark Matter Annihilation. This involves particles colliding with their corresponding anti-particles, resulting in the conversion of mass into energy according to Einstein's special relativity.
Under the influence of the gas' gravity, more hydrogen, helium and dark matter from its surroundings would be drawn towards it, allowing it to accrete more mass. This rapid accumulation allows it to grow quickly; it could grow to around 10,000 times the mass of the Sun. Due to the energy produced in annihilation as well as the heated gas, this gas would glow with a brightness that could surpass that of an entire galaxy of currently known stars.
This phenomenon is what the research group suggests as a "Supermassive Dark Matter Star" (SMDS). According to the group's research in 2008 and 2012, the spectrum of a hypothetical dark star should match that of black body radiation, because the light emitted is only related to the object's temperature. In addition, absorptions of hydrogen and helium gas are expected to cause sharp dips in the spectrum.
The launch of the JWST enabled the researchers to study more distant objects. In this recent research, their approach was to compare JWST photometric data of three formerly identified potential candidates for Population III stars (first stars purely formed from hydrogen and helium), namely JADES-GS-z11-0, JADES-GS-z12-0, and JADES-GS-z13-0, to their dark star model.
Processing the images requires the group to apply filters that allow different wavelengths through them. The group could then observe the brightness at different wavelengths, and compare the brightness ratios produced from this observation to black body emission and absorption spectrums. In doing so, the group has found that the three candidates' data fit into the dark star model, leading to their conclusion that the model explained them well. This was used to support their claim that the three observations are SMDSs and that the new class of stars exist.
However, it must be noted that the group's dark star model is built on a number of assumptions about dark matter, which may not be reliable given our little understanding of it. Moreover, the data used was only photometric data from the JWST, instead of the telescope's more precise spectral data; it will likely take time for NASA to publicise the spectral data. In order to make a stronger claim, further investigation is necessary where spectral data is to be analysed.
Presently, the hypothesis is relatively unexplored in the field, as there have not been any published papers about SMDS except those from the research group. In the future, if the hypothesis is indeed proven, SMDS could be used to explain the reionisation process, which occurred 150 million years after the beginning of the universe, allowing light to travel freely in space. The collapse of SMDSs could also be a convincing explanation for the formation of supermassive black holes compared to the current theories.
The research paper for the recent claim of discovering dark stars in JWST data can be found here. The 2008 paper on the hypothesis of dark stars' existence can be read here, and the 2012 paper estimating the number of dark stars can be read here.