Language
Country/Area
No result found
The Secret of Red Giants: How does a star transform from hydrogen to helium, triggering a violent helium flash?
In the vastness of the universe, the evolution of stars is a fascinating scientific mystery. The infinite changes and life and death of stars are always accompanied by countless energy releases and chemical transformations. Among them, the phenomenon of helium flash, especially the process of converting hydrogen into helium during the evolution stage of red giants, produces amazing energy and heat. This is an area of great concern to scientists and astronomy enthusiasts.
Red giant is an important stage in stellar evolution. When low-mass stars (such as stars with a mass between 0.8 and 2.0 solar masses) have exhausted the hydrogen in their cores, they will enter the red giant stage. During this process, helium accumulates in the cores of stars, and as hydrogen is consumed, their core structure undergoes drastic changes.
When hydrogen is consumed, the core begins to be dominated by helium. As the pressure and density of the core increase, the internal temperature will gradually rise, eventually reaching the critical temperature that can start helium nuclear fusion.
At this point, the thermal pressure of the core can no longer effectively counteract the effects of gravity, causing the star to begin to shrink and heat up. Once the core temperature reaches about 100 million Kelvin, helium can begin to fuse, a phenomenon known as the helium flash. The helium particles in the system rapidly fuse through the triple-alpha process to produce carbon, releasing energy at an unimaginable rate.
Helium flash is a brief thermal runaway nuclear fusion phenomenon that releases energy at a rate comparable to that of the entire Milky Way. This astonishing energy makes it impossible for us not to ponder the mysteries of the universe.
Because the helium flash mainly occurs deep in the core of the star, even though it releases huge amounts of energy, it is almost imperceptible to the outside world. Although this process cannot be directly observed, it provides astronomers with a wealth of data to understand the life cycle of stars.
Subsequent phenomena of helium flash
After the helium flash, the core expands and cools rapidly, while the surface of the star cools and contracts rapidly within just a few tens of centuries, during which time the core changes significantly. Typically, the helium core makes up about 40% of the mass of a star, and about 6% of the core mass is converted to carbon.
Subflashes and Red Giant Stars
After the main helium flash, there are also subflashes, which are shorter-lived pulsating instabilities that can last from hours to days, as the core changes. The changes caused by these sub-flashes cause the star to continuously change its internal structure and external radiation characteristics under unprecedented conditions.
As the red giant star further evolves, changes and reactions in the core during helium fusion continue to affect the overall dynamics of the star.
Other special circumstances
In certain binary systems, hydrogen can enter the surface of a white dwarf through the accretion of a companion star, producing a series of fusion reactions. If the amount of hydrogen reaches a certain level, it may lead to a surface helium flash. These nuclear fusion processes not only enhance our understanding of the internal structure of stars, but also help explain the generation and evolution of elements in many celestial bodies, supernovae, and galaxy formation processes.
Overall, the helium flash is an extremely fascinating astronomical phenomenon, which not only demonstrates the transformation of matter and the operation of energy in the universe, but also reflects the profound principles of stellar evolution. With the advancement of science and technology, these mysterious phenomena will continue to attract us to explore and think: In the universe we know, what unsolved secrets are waiting for us to discover?
