James Webb Telescope glimpses possible first dark stars

Stars radiate bright from the darkness of space thanks to fusion, atoms fuse together and release energy. But what if there’s another way to power a star?

A team of three astrophysicists – Katherine Freese of the University of Texas at Austin, working with Cosmin Ilie and Jillian Paulin ’23 of Colgate University – analyzed images from the James Webb Space Telescope (JWST) and found three bright objects that could be “dark stars”, theoretical objects much larger and brighter than our sun, powered by annihilating dark matter particles. If confirmed, dark stars could reveal the nature of dark matter, one of the most profound unsolved problems in all of physics.

“Discovering a new type of star is pretty cool in itself, but finding that dark matter is fueling it would be huge,” said Freese, director of the Weinberg Institute for Theoretical Physics and Jeff and Gail Kodosky Endowed Chair in Physics at UT. Austin.

Although dark matter makes up about 25% of the universe, its nature has eluded scientists. Scientists believe it is made from a new type of elementary particle, and the hunt to detect such particles is on. Weakly interacting massive particles are among the main candidates. When these particles collide, they annihilate each other, depositing heat in the collapsing hydrogen clouds and converting them into bright dark stars. The identification of supermassive dark stars would open up the possibility of learning about dark matter based on their observed properties.

The research is published in the Proceedings of the National Academy of Sciences.

Follow-up observations from JWST of the objects’ spectroscopic properties, including dips or excesses in light intensity in certain frequency bands, could help confirm whether these object candidates are indeed dark stars.

Confirming the existence of dark stars could also help solve a problem JWST created: There seem to be too many large galaxies too early in the universe to fit the predictions of the Standard Model of cosmology.

“It’s more likely that something within the standard model needs to be fine-tuned, because coming up with something completely new, like we’ve done, is less and less likely,” Freese said. “But if some of these objects that look like early galaxies are actually dark stars, the simulations of galaxy formation agree better with the observations.”

The three candidate dark stars (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 that the objects were observed at times ranging from about 320 million to 400 million years after the Big Bang, making them some of the earliest objects ever seen.

“When we look at James Webb’s data, there are two competing possibilities for these objects,” 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, a dark star has enough light to compete with an entire galaxy of stars.”

Dark stars could theoretically grow to be several million times the mass of our sun and up to 10 billion times brighter than the sun.

“In 2012, we predicted that supermassive dark stars could be observed with JWST,” said Ilie, assistant professor of physics and astronomy at Colgate University. “As shown in our recently published PNAS article, we have already found three supermassive dark star candidates during JWST data analysis for the four high-redshift JADES objects spectroscopically confirmed by Curtis-Lake et al, and I am hopeful that we will soon identify many more.

The idea for the dark stars came from a series of conversations between Freese and Doug Spolyar, then a graduate student at the University of California, Santa Cruz. They wondered: what does dark matter do to the first stars to form in the universe? Then they contacted Paolo Gondolo, an astrophysicist at the University of Utah, who joined the team. After several years of development, they published their first paper on this theory in the journal Physical Review Letters in 2008.

Together, Freese, Spolyar and Gondolo have developed a model that goes something like this: at the center of the first protogalaxies, there would be very dense clusters of dark matter, together with clouds of hydrogen and helium gas. As the gas cools, it would collapse, dragging the dark matter with it. As the density increased, the dark matter particles would annihilate more and more, adding more and more heat, which would prevent the gas from collapsing into a core dense enough to support fusion as in a normal star. Instead, it would continue to collect more gas and dark matter, becoming big, bloated, and much brighter than normal stars. Unlike ordinary stars, the energy source would be evenly distributed, rather than concentrated in the core. With enough dark matter, dark stars could grow to be several million times the mass of our sun and up to 10 billion times brighter than the sun.

Funding for this research was provided by the US Department of Energy’s Office of High Energy Physics program and the Vetenskapsradet (Swedish Research Council) at the Oskar Klein Center for Cosmoparticle Physics at Stockholm University.