Much like any living being, stars go through a natural cycle. This begins with birth, extends through a lifespan characterized by change and growth, and ends in death. For one, the timescales are entirely different, lasting on the order of billions of years. Also, the changes they go through during their lifespan are entirely different too.
RG The evolutionary tracks of stars with different initial masses on the Hertzsprung—Russell diagram. Mature stars[ edit ] Eventually the core exhausts its supply of hydrogen and the star begins to evolve off of the main sequencewithout the outward pressure generated by the fusion of hydrogen to counteract the force of gravity the core contracts until either electron degeneracy pressure becomes sufficient to oppose gravity or the core becomes hot enough around MK for helium fusion to begin.
Which of these happens first depends upon the star's mass. Low-mass stars[ edit ] What happens after a low-mass star ceases to produce energy through fusion has not been directly observed; the universe is around Recent astrophysical models suggest that red dwarfs of 0.
Instead, hydrogen fusion will proceed until almost the whole star is helium.
Internal structures of main-sequence starsconvection zones with arrowed cycles and radiative zones with red flashes. To the left a low-mass red dwarfin the center a mid-sized yellow dwarf and at the right a massive blue-white main-sequence star. Slightly more massive stars do expand into red giantsbut their helium cores are not massive enough to reach the temperatures required for helium fusion so they never reach the tip of the red giant branch.
When hydrogen shell burning finishes, these stars move directly off the red giant branch like a post- asymptotic-giant-branch AGB star, but at lower luminosity, to become a white dwarf. Red giants lie along the right edge of the Hertzsprung—Russell diagram due to their red color and large luminosity.
Mid-sized stars are red giants during two different phases of their post-main-sequence evolution: Many of these helium-fusing stars cluster towards the cool end of the horizontal branch as K-type giants and are referred to as red clump giants. Subgiant When a star exhausts the hydrogen in its core, it leaves the main sequence and begins to fuse hydrogen in a shell outside the core.
The core increases in mass as the shell produces more helium. Depending on the mass of the helium core, this continues for several million to one or two billion years, with the star expanding and cooling at a similar or slightly lower luminosity to its main sequence state.
Eventually either the core becomes degenerate, in stars around the mass of the sun, or the outer layers cool sufficiently to become opaque, in more massive stars. Either of these changes cause the hydrogen shell to increase in temperature and the luminosity of the star to increase, at which point the star expands onto the red giant branch.
Red giant branch Typical stellar evolution for 0. For all but the lowest-mass stars, the fused material has remained deep in the stellar interior prior to this point, so the convecting envelope makes fusion products visible at the star's surface for the first time. At this stage of evolution, the results are subtle, with the largest effects, alterations to the isotopes of hydrogen and helium, being unobservable.
These are detectable with spectroscopy and have been measured for many evolved stars. The helium core continues to grow on the red giant branch. It is no longer in thermal equilibrium, either degenerate or above the Schoenberg-Chandrasekhar limitso it increases in temperature which causes the rate of fusion in the hydrogen shell to increase.
The star increases in luminosity towards the tip of the red-giant branch. Red giant branch stars with a degenerate helium core all reach the tip with very similar core masses and very similar luminosities, although the more massive of the red giants become hot enough to ignite helium fusion before that point.If the star is big enough to fuse hydrogen atoms into helium, it will enter the phase that our Sun is in, called the main sequence phase.
A star will enjoy most of its life in the main sequence phase. Stars have a dynamic life cycle – they have moments of birth and moments of death.
It might sound strange that a star might actually ‘die’ but researchers and astronomers have assessed a number of stars and what they have discovered is that, rather than being all very unique, in fact there are stages which are similar, that patterns have emerged which enable them to prove that there is a.
The largest stars have the shortest lives, and can last a few billion, and even just a few million years. Red Giant: Over the course of its life, a star is converting hydrogen into helium at its core.
May 07, · A star's life cycle is determined by its mass. The larger its mass, the shorter its life cycle. A star's mass is determined by the amount of matter that is available in its nebula, the giant cloud of gas and dust from which it was born.
The life cycle of a star depends on the size and age, stars grow until the end of their lifespan.
This is a panoramic picture of a colorful assortment of , stars that are all in the core of a giant star cluster. The Expanding Family Life Cycle: Individual, Family, and Social Perspectives with Enhanced Pearson eText -- Access Card Package (5th Edition) 5th Edition.