The James Webb Space Telescope (JWST) may have spotted weird stars powered by dark matter instead of nuclear fusion. If these stars are really out there, it could solve three major cosmic mysteries in one fell swoop.
Regular stars form when a cloud of dust and gas becomes so massive that it collapses in on itself, and the pressure and temperature in the centre are high enough to begin the process of nuclear fusion, wherein atoms slam together and merge into heavier elements. So-called dark stars wouldn’t have any fusion at all – in the early universe, they could form from similar clouds rich in dark matter. For several postulated types of dark matter, when two particles collide they should annihilate in a blast of energy, which would be intense enough to power a supermassive star.
“They’re very bizarre stars – in radius they’re around 10 AU [astronomical units, the distance between Earth and the sun], so they’re puffy beasts, and there’s no core,” says Katherine Freese at the University of Texas at Austin. “They’re relatively cool throughout, and because they’re so cool there’s nothing that’s preventing accretion onto them, so they grow – they can grow to a million solar masses, a billion solar luminosities, maybe even more.”
Freese and her colleagues hunted through data on some of the most distant objects JWST has seen and found three of them that could potentially be supermassive dark stars, not galaxies as was initially assumed. JWST has found many more distant galaxies than expected, which could be a problem for our standard model of cosmology, so if some of them are actually dark stars it could solve that dilemma.
“Right now the spectra are not really good enough to tell – you’d have to look at one of these objects for a year with JWST, which is not likely to happen,” says Freese. The other way to figure it out would be to find a dark star with its light magnified by gravitational lensing, which could give us much more information.
If these objects turn out to truly be dark stars, it would be a major leap in our understanding in dark matter. “Despite decades of experiments and observations, we have yet to conclusively observe anything related to the non-gravitational nature of dark matter,” says Pearl Sandick at the University of Utah. “Observing a dark star would be an incredible confirmation that dark matter experiences forces other than gravity, and at the same time it would really confirm a very interesting and different picture of the formation of the first stars in the universe than the standard story.”
Once a dark star drifted out of the area where it formed, it would no longer have enough dark matter to act as fuel within it. “As soon as it moves, it’ll collapse, and boom – you have a black hole,” says Freese. But dark stars can, in theory, grow much bigger than regular stars, so the resulting black holes would be similarly enormous. This could provide an answer to the long-standing mystery of how supermassive black holes form in the early universe.