The Sun has been burning hydrogen fuel for a staggering 4.6 billion years and astrophysicists estimate it has another 7 to 8 billion years left before it sputters out and dies. All stars go through this lifecycle of formation, fuel consumption, and ultimate collapse — or do they?
Stars swirling in the violent galactic center of the Milky Way are exhibiting strange properties. A peculiar cluster of such stars could become “immortal” by continuously capturing and destroying dark matter particles in their cores, a new study suggests. In effect, such stars may be primarily fueled by dark matter instead of nuclear fusion.
Dark Matter Fuel
Researchers at Stockholm University in Sweden and Stanford University in California used computer simulations of stellar evolution on stars orbiting the galactic center. This is how they uncovered an intriguing phenomenon: dark matter particles, captured by these stars’ gravity, may frequently collide and “annihilate” each other inside the star. This process transforms dark matter into ordinary particles while releasing a significant amount of photons and electrons.
This exotic reaction could maintain the star’s stability, preventing its gravitational collapse at the end of its lifecycle after its regular supply of nuclear fuel runs out. The outward pressure effect could extend the star’s lifetime by up to 100-fold, making them practically immortal.
The investigation was spurred by the observation that many stars spotted near the Milky Way’s central supermassive black hole — known as Sagittarius A* and whose mass exceeds 4.3 million Suns — seem to be far younger than theories of stellar evolution predict.
Stars Defying Expectations
Stars nearby Sagittarius A* orbit around it at speeds of several thousand km/s. The origin of such inner stars, known as S-cluster stars, is shrouded in mystery due to the extreme environment at the galactic center. S-cluster stars orbit only three light-years away from the massive black hole.
To investigate this mystery, the researchers tested whether the stars could be drawing energy from the plentiful supply of dark matter thought to exist at the galactic center. The density of dark matter in a galaxy is highest near its center and decreases with distance outward. Astronomers infer its presence from the high rotational speeds of stars around the galactic center.
The computer simulations ultimately showed that the inclusion of dark matter annihilation in stellar dynamics solves many of the known inconsistencies in astronomers’ observations.
“Our simulations show that stars can survive on dark matter as a fuel alone,” said lead co-author Isabelle John from Stockholm University, “and because there is an extremely large amount of dark matter near the Galactic Center, these stars become immortal, staying forever young, occupying a new, distinct, observable region of the HR diagram.”
John also noted that lighter stars might become very ‘puffy’ and lose parts of their outer layers. This phenomenon could explain the mysterious, so-called G-objects near the galactic center. These appear star-like but are surrounded by gas clouds.
Currently, observing individual stars close to the galactic center is difficult due to the high brightness of the area. However, upcoming telescopes will offer clearer views, allowing scientists to better understand this stellar population and verify the existence of the “dark main sequence”.
This study was published on the preprint server arXiv in May and has yet to undergo peer review.
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