For the first time, researchers from the University of Granada and the Andalusian Institute of Astrophysics have studied the music of a pulsating star with the help of fractals.
Scientists say that the stars emit a continuous whispering noise in the background. They have managed to isolate stellar music from noise in an efficient and simple way, using an algorithm to better identify variable stars.
In nature, fractal behavior appears frequently, from the geometry of a cauliflower to the profile of a mountain or the ramifications of rivers. Having a fractal behavior means that they have a similar structure to all scales (that is, scale invariance), so that, observing them through a magnifying glass or a telescope, we would not notice a difference.
Most stars are pulsating variables (as is our own Sun), that is, their luminosity varies periodically over time. This is because waves of density and temperature that are generated inside reach the surface of the star causing it to oscillate, causing changes in its brightness. These stellar oscillations form three-dimensional patterns just like a guitar string or the skin of a drum in one and two dimensions respectively.
Experts from a branch of astrophysics called astroseismology, have analyzed these luminosity oscillations, trying to classify pulsating stars into different types, each one with a certain internal structure and physical properties, in the same way through which our ear can identify different musical instruments in an orchestra, and therefore, the properties of each of them, such as material or dimensions.
But in the background of stellar music there is more. As explained by Juan Carlos Suárez Yanes, researcher at the Department of Theoretical and Cosmos Physics at the UGR, and Sebastiano de Franciscis, from the IAA-CSIC, "The music of a pulsating star turns out to have a continuous whispering noise in the background, like an annoyed audience in a concert hall, which makes listening difficult".
Better characterize variable stars
Researchers have applied an algorithm based on Fourier harmonic analysis (which studies the representation of functions or signals as superposition of “basic” waves or harmonics) of time series with fractal properties to isolate stellar music from annoying background noise. in an efficient and simple way. This makes it possible to debug the oscillations that are part of the noise from stellar music, and thus better identify and characterize variable stars.
Thanks to this method, researchers can better identify and characterize variable stars. This is an important step to understand more and more the physical mechanisms that govern pulsating stars, since it is now possible to see more clearly inside them.
S. de Franciscis, J. Pascual-Granado, J. C. Suárez, A. García Hernández, R. Garrido, M. Lares-Martiz, J. R. Rodón, "Physical insights on fractal analysis applied to light curves δ Scuti stars"Monthly Notices of the Royal Astronomical Society, (2019), In Press.