From Bright Red Giants to Mysterious Carbon Stars: Unveiling Stellar Secrets

#Astronomy #StellarEvolution #RedGiant #CarbonStars #Astrophysics #StarLifecycle #SpaceScience #VariableStars #MiraStar #Cosmology
In this short snippet of an upcoming video, I delve into the fascinating and intricate life cycle of a sun-like star as it rapidly ascends the asymptotic giant branch (AGB) during a brief 20 million year period. I explain how the core of the star contracts and heats up, with nuclear fusion occurring in a helium-burning shell while the star’s outer layers expand and become cooler yet brighter. If this were our Sun, its outer layers would nearly reach Earth’s orbit, dragging Earth into its doom during its red giant phase, leaving Mars next in line. I illustrate how the star’s surface temperature plummets to around 3200 Kelvin, yet its luminosity dramatically increases due to the intense heat from the helium shell burning. The strong luminosity drastically shortens the star’s lifespan during this evolutionary phase, resulting in faster burning and a quicker journey through this stage. The hydrogen-burning shell intermittently reignites, the helium shell flashes repeatedly, driving dynamic changes in the star’s luminosity. I further delve into the process of helium shell flashes, where helium ash accumulates and ignites, temporarily cooling the hydrogen-burning shell. This cyclical process varies in duration depending on the star’s mass, with higher-mass stars experiencing pulses every few thousand years, while lower-mass stars may take hundreds of thousands of years between pulses. Each pulse increases the luminosity dramatically for a short time, followed by a drop as observed in various luminosity graphs. These processes lead to fascinating phenomena observed in carbon-rich stars, displaying significant spectral features in the red end, aiding in cosmological studies. Carbon stars act as standard candles in the HR diagram, helping resolve cosmic measurements. I also highlight the importance of observing variable stars, particularly Long Period Variables (LPVs), which have periodic luminosity changes and significantly contribute to our understanding of stellar behavior. Observing Mira or Omicron Ceti, a well-known LPV, shows the dramatic variability of such stars over time and reveals intriguing mass-loss interactions creating bow shocks. Finally, I touch on the significance of hydrogen ionization and recombination processes seen in Mira’s space velocity and motions, inviting you to explore further in my series on the interaction of atoms and light.