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WHAT IS A DARK MATTER STAR??
Blog#490
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Saturday, March 22nd, 2025.
In a first, the James Webb Space Telescope (JWST) might have glimpsed a rare type of star that astronomers aren’t even sure exists. These stellar objects, called dark stars, might have been fueled not by nuclear fusion but by the self-annihilation of dark matter—the invisible stuff that is thought to make up about 85 percent of the matter in the universe.
Scientists will need more evidence to be able to confirm the candidates seen by JWST, but if these dark stars are real, the finding could change our story of how the first stars formed.
Contrary to their name, dark stars could have glowed a billion times more luminously than the sun and grown to a million times its mass. Dark stars have never been definitively observed, but cosmological simulations suggest that they should have formed soon after the big bang from clouds of pure hydrogen and helium that collapsed at the centers of protogalaxies rich in dark matter.
In July 2023 researchers reported in the Proceedings of the National Academy of Sciences USA that at least three far-off objects observed by JWST and previously identified as galaxies could, in fact, each be a single, supermassive dark star. “If you find a new kind of star, that’s huge,” says study co-author Katherine Freese, an astrophysicist at the University of Texas at Austin.
The researchers can’t yet prove that the objects are dark stars—only that their characteristics are consistent with their being either dark stars or galaxies populated by regular fusion-powered stars. JWST’s technology is sufficient to do that job, however, says study co-author Cosmin Ilie, an astrophysicist at Colgate University.
All researchers need is more observation time. “We hope we are going to find one of these dark stars with the Webb within its lifetime,” Ilie says.
There are two possibilities for how the first stars in the universe formed. The conventional wisdom is that these early stars were “Population III” stars. Such stars would have been powered by nuclear fusion, like stars today, but they would have had very little to no metal in them—in astronomy, that means elements heavier than helium—because those elements had not yet formed in the early universe.
There is another possibility, though. In 2008 Freese and some of her colleagues proposed that the universe’s first stars could have been powered by dark matter. Dark matter is a mysterious form of matter that does not interact with electromagnetic forces; scientists know it exists only because of its gravitational effects, and they don’t know what it’s made of.
In the early universe, dark stars could have formed from the collapse of helium and hydrogen clouds made in the big bang. If dark matter particles are also their own antiparticles, as many dark matter theories posit, then within these collapsing clouds, those particles would have collided with one another and self-annihilated.
The collision would have kicked off a chain of particle decay that ended with the production of photons, electron-positron pairs and neutrinos. Only the neutrinos would have really left the cloud because they barely interact with matter. The other particles would have hit the hydrogen and helium and transferred their energy to that matter, which would have heated up the cloud and fueled the star’s formation and continued growth.
These stars would have formed at the center of “minihaloes,” which were early protogalaxies that existed 200 million years after the big bang, before the advent of elements heavier than helium and hydrogen. These minihaloes consisted almost entirely of dark matter, making conditions within them ripe to power dark stars. This high concentration of dark matter is why dark stars could form only in the early universe, Freese says.