The first generation of stars in the Universe is yet to be observed. There are two leading theories for those objects: hydrogen burning Population III stars and the so-called ‘dark stars,’ made of hydrogen and helium but powered by dark matter heating rather than by nuclear fusion. New research shows that JADES-GS-z13-0, JADES-GS-z12-0, and JADES-GS-z11-0 — three high-redshift galaxy candidates detected by the NASA/ESA/CSA James Webb Space Telescope — are consistent with a supermassive dark star interpretation, thus identifying the first dark star candidates.
An artist’s impression of a supermassive dark star. Image credit: Sci.News.
Dark matter is the mysterious substance that makes up about 25% of the Universe.
There is strong indirect evidence for its existence from measurements of cosmic primordial radiation, anomalies in the radial dependence of galactic rotational curves and gravitational lensing.
Despite its apparently pivotal role in the Universe the physical origin of dark matter remains unknown.
Theoretical physicists suspect that it is made of unseen particles that neither reflect nor absorb light, but are able to exert gravity.
Experiments around the world are attempting to detect and study such particles. Among the leading candidates are WIMPs (weakly interacting massive particles).
When they collide, these particles annihilate themselves, depositing heat into collapsing clouds of hydrogen and converting them into brightly shining dark stars.
The identification of supermassive dark stars would open up the possibility of learning about the dark matter based on their observed properties.
Follow-up observations from Webb of the objects’ spectroscopic properties could help confirm whether these candidate objects are indeed dark stars.
Confirming the existence of dark stars might also help solve a problem created by Webb: there seem to be too many large galaxies in the early Universe to fit the predictions of the Standard Model of cosmology.
“It’s more likely that something within the Standard Model needs tuning, because proposing something entirely new, as we did, is always less probable,” said Dr. Katherine Freese, an astrophysicist at the University of Texas at Austin.
“But if some of these objects that look like early galaxies are actually dark stars, the simulations of galaxy formation agree better with observations.”
JADES-GS-z13-0, JADES-GS-z12-0, and JADES-GS-z11-0 were detected by the JWST JADES program. Image credit: Robertson et al., arXiv: 2212.04480.
JADES-GS-z13-0, JADES-GS-z12-0, and JADES-GS-z11-0 were originally identified as galaxies in December 2022 by the JWST Advanced Deep Extragalactic Survey (JADES).
Using spectroscopic analysis, the JADES team confirmed the objects were observed 320 to 400 million years after the Big Bang, making them some of the earliest objects ever seen.
“When we look at the Webb data, there are two competing possibilities for these objects,” Dr. Freese said.
“One is that they are galaxies containing millions of ordinary, Population III stars. The other is that they are dark stars.”
“And believe it or not, one dark star has enough light to compete with an entire galaxy of stars.”
Dark stars could theoretically grow to several million solar masses and up to 10 billion times as bright as the Sun.
“We predicted back in 2012 that supermassive dark stars could be observed with Webb,” said Dr. Cosmin Ilie, an astrophysicist at Colgate University.
“Discovering a new type of star is pretty interesting all by itself, but discovering it’s dark matter that’s powering this — that would be huge,” Dr. Freese said.
This research is described in a paper in the Proceedings of the National Academy of Sciences.
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Cosmin Ilie et al. 2023. Supermassive Dark Star candidates seen by JWST. PNAS 120 (30): e2305762120; doi: 10.1073/pnas.2305762120
