Recent research suggests that exotic stars, potentially powered by dark matter, could exist in the early universe. These so-called dark stars may offer insights into some of the cosmos’ greatest mysteries, including the formation of supermassive black holes. The findings were led by a team headed by Katherine Freese at the University of Texas at Austin and published in a prominent scientific journal.
Normal stars are formed when a gas cloud collapses, leading to a dense core that ignites nuclear fusion. In contrast, dark stars could have emerged during a denser epoch of the universe, where dark matter was prevalent. If a collapsing gas cloud contained sufficient dark matter, its annihilation could release energy before nuclear fusion begins, allowing the dark star to shine and resist gravitational collapse.
The research explored how dark stars might evolve. In conventional massive stars, the depletion of hydrogen and helium leads to the fusion of heavier elements until they collapse into black holes. However, dark stars can potentially evade such fates. As noted by George Fuller from the University of California, San Diego, adding dark matter as a power source could allow a dark star to avoid the nuclear evolution that typically leads to instability.
According to Einstein’s theory of general relativity, gravity does not simply increase with mass; it can create complex gravitational fields. This means that dark stars, while resilient for a time, will eventually become unstable when reaching a mass between 1,000 and 10 million times that of the sun. This mass range positions dark stars as strong candidates to explain the formation of supermassive black holes, some of which astronomers have observed dating back to the universe’s infancy.
The presence of enormous black holes so early in cosmic history raises questions about their formation. Katherine Freese emphasized the challenge: “If you have a black hole of 100 solar masses, how do you get to 1 billion solar masses in a few hundred million years? It’s just not possible if you’re only making black holes from standard stars.” Dark stars could serve as “seeds” for these massive black holes, enabling their rapid growth.
Additionally, the James Webb Space Telescope (JWST) has identified two unusual types of distant objects, informally referred to as “little red dots” and “blue monsters.” Initial analyses suggest these could also be extremely massive dark stars rather than compact galaxies, as their formation would seem improbable given the early universe’s timeline.
The team led by Katherine Freese found potential evidence of a specific light absorption signature in JWST’s observations, which would indicate the presence of dark stars. Regular stars are too hot to exhibit this signature, but the data remains inconclusive due to noise. “Right now, all the candidates that we have could fit the spectra equally well: one supermassive dark star or an entire galaxy of regular stars,” Freese explained.
While the current findings do not confirm the existence of dark stars, they represent a promising lead. According to Dan Hooper from the University of Wisconsin-Madison, “This isn’t some profound, unambiguous smoking gun, but it’s a really well-motivated thing that they’re looking for.”
Researchers emphasize the need for additional observations to determine if these potential dark stars exist. Volodymyr Takhistov from the High Energy Accelerator Research Organization highlighted the significance of confirming dark stars, stating that their discovery could open new avenues in understanding the universe’s fundamental physics, particularly regarding dark matter.
The team theorizes that the mass at which dark stars would collapse into black holes is related to the characteristics of the dark matter particles annihilating at their cores. This means that if dark stars are confirmed, they could help measure or constrain our understanding of dark matter’s properties.
In conclusion, while the existence of dark stars remains to be seen, the research provides a compelling foundation for future exploration. “If these things are out there, they’re rare,” Hooper remarked. “Rare, but extraordinary.”
