This sequence shows snapshots of a star’s density when two dark matter cores collide, where the x-axis is the plane of collision (only half the space is shown, but the remaining space can be obtained by symmetry). Although the final configuration is more compact and massive than the original, the star does not collapse into a black hole because it ejects some of its mass, slowing down its growth so that it remains stable. Credit: Brito, et al. ©2015 American Physical Society Read more at: http://phys.org/news/2015-09-dark-stars-oscillations.html#jCp
Large amounts of hidden mass inside stars might be composed of extremely lightweight hypothetical particles called axions, which are a primary dark matter candidate. “Our work studies how dark matter piles up inside stars if the dark matter is composed of massive bosonic particles (axions are an example of such particles),” said scientist Brito. “Our results show that dark matter accretion by stars does not lead to gravitational collapse; instead it may give rise to characteristic vibrations in stars.”
The researchers theoretically showed that, if numerous axions were to pile up inside normal stars, then the dark matter core would oscillate, causing the star’s fluid to oscillate in tune with it at a specific frequency related to the star’s mass, or at multiples of this frequency. For a typical axion mass, the oscillating stars would emit microwave radiation and might have observable effects.
“What oscillates is the fluid density and its pressure, but it’s probably correct as well to say that the entire star is oscillating,” Brito explained. “These are like sound waves propagating through the fluid, with a very specific frequency. Oscillations of this kind could, for example, lead to variations in the luminosity or in the temperature of the star, and these are quantities that we can measure directly. “In fact, there is already a whole branch of physics called asteroseismology, which studies the internal structure of stars by observing their oscillation modes… It is possible that the oscillations of a star driven by a dark matter core could also be observed using similar methods. Given the very specific frequencies at which these stars would vibrate, this could be a smoking gun for the presence of dark matter.”
Unlike previous studies, the new physicists’ simulations showed stars accreting dark matter do not eventually collapse into black holes. Their stability arises from a self-regulatory mechanism called “gravitational cooling” in which the stars eject mass to slow down and stop their growth before they approach the critical Chandrasekhar limit, the point at which they collapse into black holes.
“We want to understand in depth how the dark matter core grows for different kind of scenarios, and how viscosity in the star’s material affects the development of the accretion process.”
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.111301
http://phys.org/news/2015-09-dark-stars-oscillations.htmljCp
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