Since 2007, astronomers have proposed the existence of a weird type of star: one powered by the heat of dark matter. In cosmology, dark matter is a difficult thing to explain because we literally don't know what it is. We can't see it, hence the name "dark," but without it factored into our equations of the universe, things just don't add up. Learning how certain so-called "dark stars" form would be a major win for better understanding our place in the cosmos. Now, the James Webb Space Telescope (JWST) may have just proven that dark stars exist.
The ancient universe was very different than it is today. Some astronomers believe that before our solar system existed — indeed, before our galaxy was formed — dark stars were abundant. According to this theory, dark stars would have been fueled by large quantities of dark matter that would generate heat. This heat in turn would prevent dark stars from turning into modern stars — the bright, burning kind fueled by nuclear fusion — and, instead, to become enormous clouds of molecular hydrogen and helium.
The first stars in the universe may have been much cooler and powered by the annihilation of dark matter
If these dark stars still exist today, they would be too cold and dark to be easily detected. Only their gamma ray, neutrino and antimatter emissions would reveal their existence, as might perhaps the presence of cold molecular hydrogen gas. A new study in the journal PNAS suggests that, thanks to the power of the James Webb Space Telescope, we may have identified three entities that might very well be lingering dark stars.
Theoretical physicist Katherine Freese, coauthor of the paper and a physics professor at both the University of Texas and Stockholm University, has been pursuing different ways to detect dark matter since her career began in the '80s. In a 2008 paper in the journal Physical Review Letters, she and her colleagues proposed a "new phase of stellar evolution," in which the first stars in the universe are much cooler and powered by the annihilation of dark matter.
One of the leading theories about dark matter is that it's composed of a type of particle known as a WIMP, or Weakly Interacting Massive Particle. When two WIMPs collide, they can annihilate each other, transforming into other particles. This would generate energy that is different from the fusion process that powers modern stars (including our own), in which hydrogen atoms combine under extreme heat and pressure to form helium. However, until the James Webb telescope came along, there has been no direct evidence supporting this theory about dark stars.
"Nothing has been proven for sure by our paper," Freese explained to Salon in an email, but it is some of the strongest evidence for dark stars to date. Back in 2007, Freese and her fellow coauthor Cosmin Ilie (then her graduate student at the University of Michigan) determined what a dark star would look like in the JWST. Once the telescope had enough data to test their theories, Freese and Ilie began sifting through the new information.
"JWST has found roughly 700 high redshift objects (i.e. from very early in the Universe)," Freese said. "Of these, one of their instruments has been able to measure spectra (i.e. the intensity at different frequencies) for 9 of them, thereby for sure proving that they are indeed from the early Universe."
Five of those nine produced useable data, and from there the researchers studied four of them as JADES objects, which stands for the James Webb Advanced Extragalactic Survey. In the end, Freese said, they determined that "three of them are a good match to our predictions for dark stars."
Those three objects include JADES-GS-z13-0, JADES-GS-z12-0 and JADES-GS-z11-0. The authors ruled out the possibility that their readings were somehow messed up by a low redshift contaminant, and they similarly found "smoking gun" features that their previous research had anticipated would signify the presence of dark stars. The study concludes with a bold proclamation: "The confirmation of even a single one of those objects as a Dark Star (with detailed NIRSpec spectra) would mark a new era in astronomy: the observational study of DM–powered stars."
"The discovery of a new type of star, made of hydrogen and helium but powered by dark matter, would be a huge advance."
"The discovery of a new type of star, made of hydrogen and helium but powered by dark matter, would be a huge advance," Freese added, echoing the enthusiasm in her paper. "As yet it is not possible to distinguish dark stars from early galaxies; as yet both are possible explanations for the data. Better spectra in the future will enable discovery of a helium line in the data — that would be a smoking gun for dark stars."
The research team — which included Freese, Ilie and Jillian Pauline from Colgate University —suggests that these dark stars would not be lit by nuclear fusion, but rather would be much more massive than most stars, so large they could even resemble galaxies from Earth-based telescopes. The researchers also argue that the dark stars collapse into supermassive black holes when they get older, which would explain why there are so many black holes in the universe.
This is hardly the first ancient celestial discovery that would have been made possible by the JWST. Speaking with Salon earlier this week, NASA official Dr. Michelle Thaller explained why she is particularly fond of some "splotches" that may be among the oldest known objects in the universe.
"The confirmation of even a single one of those objects as a Dark Star would mark a new era in astronomy."
"The Big Bang was only about 13.8 billion years ago. So we're looking back to the very, very early youngest galaxies here," Thaller told Salon at the time. "The thing that blows my mind about these splotches is that I never thought I would be able to actually see an image of this, when I was in astronomy grad school and we were learning about what happened in the very earliest part of the universe."
Freese also praised the JWST in her interview with Salon, making it clear that it alone was technologically advanced enough to acquire this data.
"JWST is the only telescope as yet capable of seeing far enough back in the universe to discover dark stars," Freese told Salon, adding that other telescopic instruments currently being developed may also serve that purpose, such as Roman and EUCLID.
"As yet all we know for sure is that objects have been found in JWST that are the earliest ever to form in the universe," Freese concluded. "We don't know anything more about their past evolution, until we know for sure what these objects are."
