The children's song "Twinkle, Twinkle, Little Star" has helped calculate how convection in stars causes variations in their brilliance. It also disproved assumptions about the causes of "red noise" in massive stars.
The atmosphere of our planet bends light, so it seems to us that the stars in the night sky twinkle. In space, this effect does not exist, so the images from space telescopes are much clearer. In fact, the stars are really "winking" on their own. These light changes are so small that even the best modern telescopes cannot detect them. But the next generation of telescopes will be able to detect them.
Although we can't see this variability, we understand that it's triggered by processes deep within the stars. "Movements that start in the cores of stars trigger ocean-like waves. When these waves reach the surface of the star, the star starts to wink, and these changes in brilliance astronomers are likely to be able to observe," explains lead author of the new paper Evan Anders (Evan Anders) from the Center for Interdisciplinary Research in Astrophysics (CIERA, USA).
Together with a team of scientists from the Flatiron Institute (USA) and Northwestern University (USA), he created the first computer model of processes in the depths of stars, which can be used to determine how much variability in the luminosity of their surface. In turn, when scientists can observe the light variations of a particular star, the same model can be used to calculate the processes in its interior.
Convection, or mixing of matter in stars, occurs due to thermonuclear reactions in the core. There, under great pressure, heavier elements are synthesized from the nuclei of hydrogen atoms, releasing energy. This energy heats up the matter and it begins to rise and stir. Waves from these processes reach the surface, where the differential pressure of the plasma changes its brightness - and the star "winks".
The complexity of such calculations is that near the core waves are formed within weeks, and to the surface they "creep" hundreds of thousands of years. Combining such different time periods in one model is not easy. According to the authors, they were inspired by sound waves. In particular, the work of an orchestra and a professional sound engineer. In this analogy, the musicians are the creators of the waves, and the sound engineer is the filter of the "acoustic properties" of the star.
The researchers tested their method first on music: "Jupiter" from Gustav T. Holst's symphonic suite and the children's song "Twinkle, Twinkle, Little Star." The scientists modeled how these sound waves would propagate in stars. Then the model was run on waves from convection for stars of different masses: three, 15 and 40 times more massive than the Sun - and in the brilliance of the stars appeared variability.
In general, the creation of the model was started in order to explain the formation of "red noise" - unexplained pulsation of brightness of hot, massive stars. It was thought that it was convection at the core that provokes this variability, but the new model showed that the deep processes do not produce such strong light variations on the surface. This means that we need to look for another cause of the "red noise".
However, the co-author of the study Matteo Cantiello (Matteo Cantiello) from the Center for Computational Astrophysics at the Institute Flatirona admits that the cause may still be convection near the surface, but then on this "red noise" we can learn little about the internal processes of stars.
Now the researchers are improving the model. First of all, they want to take into account in the calculations of the rapid rotation of stars. Perhaps the variability of light in such objects is stronger, and it will be possible to detect it with modern telescopes.
Massive stars at the end of their "life" explode, throwing valuable heavy elements into space, and turn into neutron stars or black holes. To accurately calculate the nature of this event and its consequences, it is necessary to know as much as possible about the internal structure of the object and its evolution. The new model will make it possible to test different scenarios of internal processes.