Some Astronomers Claim Dark Star Candidates in Webb Images

A trio of astrophysicists has identified three possible “dark stars” — stars powered by dark matter rather than fusion — skulking in James Webb Space Telescope observations of the early universe. If true – and right now that's a big if – it could solve multiple cosmological puzzles at once.

Despite launching less than two years ago, Webb is already tantalizing astronomers with unexpected results. Astronomers have used it to look back to a few hundred million years after the Big Bang and they quickly found that too many bright galaxies had already formed, earlier than our standard cosmological models predict. There were also indications that some early galaxies were too massive, but that hasn't panned out as the JWST JADES survey progressed.

What if some of these unexpected galaxies aren't galaxies at all? That’s what Cosmin Ilie and Jillian Paulin (both Colgate University) and Katherine Freese (University of Texas at Austin) suggest in the Proceedings of the National Academy of Sciences. They argue that three “galaxies” seen with Webb could in fact be single, supermassive stars powered by dark matter.

The primary evidence is that these light sources appear unresolved — in other words, whatever’s emitting the light is very small in size. The light in different wavebands also matches what theorists, including Freese, had predicted for dark stars.

“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,” Freese says.

Dark matter is one the biggest mysteries in cosmology. Often astronomers need an extra source of gravity to help bind structures in the universe together, so they invoke the presence of an invisible glue that's been around since the beginning of the universe.

For decades the leading candidate for dark matter has been weakly interacting massive particles (WIMPs). When two WIMPs meet, they can annihilate, converting their mass into energy. If WIMPS do indeed exist, here's a possible scenario for how things could have unfolded in the early universe.

Primitive clouds of hydrogen would have been laced with WIMPs, at a level of about 0.1% . As those clouds collapsed under their own gravitational pull, WIMP annihilations ramped up and the energy released heated the cloud. This prevented the cloud from collapsing far enough to reach the temperatures and pressures required for fusion, the normal nuclear reactions that power stars. Instead of an ordinarystar, the cloud would have formed an enormous dark star, powered entirely by dark matter annihilations.

“One dark star has enough light to compete with an entire galaxy of stars,” Freese says, who helped name these objects after Grateful Dead’s song “Dark Star.” Theoretically, they could grow to millions of times the mass of the Sun and shine 10 billion times as brightly. At first glance they could even be mistaken for protogalaxies.

For Illie this has been a long time coming. “We predicted back in 2012 that supermassive dark stars could be observed with JWST,” he says. “I am confident we will soon identify many more [dark star candidates].”

Candidates is the operative word here. The team aren't claiming to have found dark stars just yet, only that the three objects are "consistent” with being dark stars. “Proposing something entirely new is always less probable,” Freese says. “But if some of these objects that look like early galaxies are actually dark stars, the simulations of galaxy formation agree better with observations.” Another strength of this idea is that it invokes the most ordinary type of dark matter, without introducing even more exotic physics.

“Dark stars are a very plausible consequence of our current cosmological model,” says Tanja Rindler-Daller (University of Vienna, Austria), who was not involved in the research. “High-quality spectra at redshifts beyond z ~ 10 will be required in order to determine finally whether they exist,” she adds. Illie's team argue that a helium-II absorption feature at 1640 Å would be a tell-tale characteristic of a hot, supermassive dark star.

“I don't think the evidence presented is especially in favor of dark stars, but it does not rule it out,” says Alexander Ji (University of Chicago), who was also not involved in the research. “If confirmed, this could completely change our picture of the early universe, as well as provide clear constraints on the nature of dark matter. So it's a small chance of a huge impact.”