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Pulsars are "listening" to the universe
Pulsars are rapidly rotating neutron stars that emit radio signals as regular as cosmic clocks.
As gravitational waves pass through space, they cause tiny shifts in the arrival times of these signals on Earth. By monitoring multiple pulsars over long periods, astronomers have detected a nanohertz gravitational wave background spanning the universe.
The problem of black holes appearing too early
The James Webb Space Telescope has detected numerous supermassive black holes that existed when the universe was still very young.
This poses a challenge to current models, as such black holes should have required a vast amount of time to grow. One possibility is that they formed from massive black hole seeds early in cosmic history.
Dark stars could be the solution
Dark stars are a hypothetical type of star powered by the interaction of dark matter rather than relying primarily on nuclear fusion.
According to some models, they could grow to hundreds of thousands or millions of times the mass of the Sun before collapsing into giant black holes. These black holes could then serve as seeds for today's supermassive black holes.
Traces left behind in gravitational waves
New simulations suggest that if dark stars were once common in the early universe, their descendants could contribute significantly to the gravitational wave background currently observed by PTAs.
If this hypothesis is correct, gravitational waves not only record modern black hole mergers but also preserve information about objects that existed at the dawn of the universe.
A new window into the past
Researchers suggest that the number of black hole seeds originating from dark stars cannot be excessively high, or the gravitational wave background would be stronger than observed. Conversely, if there are too few, other mechanisms would be needed to explain the early emergence of supermassive black holes.
Instead of directly searching for long-vanished dark stars, astronomers are using gravitational waves as a "cosmic fossil" to help explore the earliest chapters in the formation history of the universe.
🌌 If confirmed, dark stars could become the missing link between dark matter, the earliest black holes, and the gravitational wave background echoing across the universe today.
