A special cluster of stars swirling around the violent center of the Milky Way could become “immortal” by continually capturing and destroying dark matter particles in their cores, a new study suggests.
Researchers discovered this using computer simulations of stellar evolution dark matter particles captured by the gravity of these stars can often collide and ‘destroy’ each other within the star, turning into regular particles while releasing a significant amount of energy.
This additional energy source could maintain the star’s stability and possibly make it immortal even after its regular supply of nuclear fuel is used up, the researchers suggest.
‘Stars burn hydrogen nuclear fusion”, lead author of the study Isabelle Johannes, a doctoral candidate in astroparticle physics at Stockholm University, told LiveScience via email. “The outward pressure of this balances out the inward pressure of the gravitational forces and keeps the stars in a stable equilibrium.”
However, it appears that many stars observed near the Milky Way’s central black hole are much younger than theories of stellar evolution predict. To investigate this mystery, the researchers tested whether the stars could draw energy from the abundant supply of dark matter believed to be present at the galactic center.
‘Our simulations show that if stars can accumulate large amounts of dark matter, which is destroyed within the star, this can create a similar outward pressure, making the star stable through the destruction of dark matter rather than through nuclear fusion. So stars can use dark matter as a fuel instead of hydrogen,” said John. ‘The important difference is that stars use up their hydrogen, which will eventually kill them. On the other hand, stars can continuously accumulate dark matter.’
The study, published on the preprint server arXiv in May, has not yet been peer-reviewed.
Stars that defy theory
Stellar evolution is a well-studied subject. Relationships between a star’s age, brightness, size and temperature have been derived with high precision, based on both theory and astronomical data. However, recent observations have shown that the properties of stars near the center of the Milky Way defy the generally accepted theory of stellar evolution.
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‘The innermost stars of our Milky Way, the stars of the S cluster, exhibit a series of properties that do this [are] found nowhere else: it is not clear how they got so close to the center, where the environment is thought to be quite hostile to star formation,” John explained. “They also appear to be much younger than what would be expected if the stars had moved there from elsewhere. Moreover, it seems as if there are an unexpected number of massive stars.”
These strange properties of the stars of the S cluster can be explained by the presence of an additional energy source in them. For example, this extra energy source could cause the star to burn hydrogen – its usual energy source – at a slower rate, making it age more slowly and look younger than it actually is.
In their recent research, John, along with Tim Linden from Stockholm University and Rebecca K. Leane from the SLAC National Accelerator Laboratory at Stanford University, suggested that this source could be the destruction of dark matter particles. This explanation is consistent with the fact that larger amounts of dark matter are believed to be lurking in the center of the Milky Way, right where the strange stars were observed.
“In most of the Milky Way, the density of dark matter is not high enough to affect stars,” says John. ‘But in the Galactic Center the amount of dark matter is very high, possibly many billions of times higher than on earth.”
Virtual destruction
To test their hypothesis, the researchers ran a computer simulation of the life cycle of a star surrounded by a dark matter cloud with a density similar to that of the galactic center. They assumed that dark matter consists of weakly interacting massive particles, one of the leading candidates for dark matter components.
Because dark matter particles have not yet been found in laboratory experiments, the strength of their interaction with ordinary matter and the rate at which they destroy each other are not known. But the study showed that for certain values of these quantities, the dark matter-based mechanism of energy production perfectly explained the observed properties of the S-cluster stars.
However, to confirm their statement, the authors believe that more stars need to be discovered near the galactic center. In addition, more accurate measurements of the parameters of known stars must be made to reliably compare observations with theoretical predictions. Hopefully, such observations will be possible in the near future using the Very Large Telescope in Chile or the Keck Observatory in Hawaii, the researchers said.
“More accurate observations of the S cluster stars will give us more information about these stars and the ongoing processes,” John said. “This will reveal whether the observations are consistent with our simulations, or whether other explanations for their unusual properties become more favorable.”