astronomers have discovered that the cause of the long-term brightness fluctuations in the old (red giants) stars is a companion rotation around them in the form of a companion star or a giant exoplanet.
results of the research stated that for many stars that belong to the categories (red giants) and the red giant planets, astronomers observed changes in brightness at different intervals, from several days to several years.
research provided a typical example of this, which is the variable star (Betelgeuse), which constantly attracts the attention of astronomers. This planet has several brightness cycles, one of which is about 185 days and the other is about 425 days. These vibrations are caused by sound waves that occur inside the star as it expands and contracts again as the hydrogen envelope burns out.
When stars of medium mass, which are eight times lighter than the sun, reach the end of their lives, the nuclear fusion of hydrogen and helium inside the star stops and the star’s core begins to shrink. But this compression brings new hydrogen to the inner region of the star, which forms a hydrogen jacket around the core.
In this case, thermonuclear fusion resumes, and the star begins to expand again until the hydrogen envelope burns out. Thus, cycle after cycle.
But in addition to short cycles of changes in brightness, astronomers also observe steady, long-lasting pulses in about one-third of the stars known as the red giants. In Bethel Gemini, this “long secondary period” lasts 5.9 years. Scientists have suggested various reasons to explain the long flash, such as internal vibrations, magnetic activity, or the presence of a companion, but none of these hypotheses has yet been confirmed