Knowing the phases and processes that a star goes through throughout its entire existence allows us to know what each stellar evolution is like.
Stellar evolution is the expression that refers to the transformations that occur in stars over the years. As time passes, each star experiences changes in its external appearance, in addition to modifications in its internal structure.
As researchers specialized in astronomy have been discovering, there are nuclear phenomena that influence stellar life . There are phases and reactions (framework in which there are alterations in composition , temperature, etc.) that become evident in the stars .
The gravitational force , as well as the nuclear force , affect stellar evolution by compressing a star until it reaches the so-called gravitational collapse without leaving aside the variations in thermal pressure.
When studying the mutations of each star, it is key to focus on its initial mass, the metallicity it presents and the rotation speed it reaches, in addition to observing whether there are companion stars nearby or not.
Phenomena associated with stellar evolution
There are several elements and phenomena associated with stellar evolution .
It is curious, to describe a specific example, the case of binary stars , which constitute a special object of interest for those dedicated to stellar astrophysics . Although it is possible to detect certain pairs of stars that orbit at a reasonable distance from each other and that allows them to change independently, in many circumstances the stellar separation is extremely short and stellar evolutions are altered or conditioned based on the mutations of every star you have as a companion. It is believed that binary stars are systems that are born at an early stage, during the time in which the protostar forms and the molecular cloud fragments.
It is also captivating to focus attention on neutron stars that are recognized as a type of pulsars and are called magnetostars . This variety, equipped with strong magnetic fields and a relatively slow rotation speed, has a short active life. It arises, according to experts' theories, within the framework of a supernova explosion (and the subsequent process of gravitational collapse ) due to the intensification of the magnetic field of a certain precursor star.
Stars that have a high mass and solar metallicity culminate their existence as a red supergiant and when it is no longer possible to obtain energy from a nuclear reaction, a so-called gravitational collapse supernova occurs. In most cases, in this framework, a neutron star will emerge as a stellar remnant.
star formation
A process very close to that of planetary formation is known as star formation . The phenomenon involves the collapse of enormous masses of gas present in galaxies through long molecular clouds recognizable in the interstellar medium . Currently, the theory states that star formation occurs from giant molecular clouds composed, essentially, of helium and molecular hydrogen .
In particular, triggered star formation is distinguished (a scenario that can unfold as a consequence of a supernova explosion or due to the collision of molecular clouds with each other), as well as self-propagating star formation if supernova production by stars is observed. new.
It is also worth knowing that in a galactic nucleus, star formation can present a rhythm regulated by the action of a supermassive black hole present in the core (or heart) of a galaxy.
Phases and sequences of stellar evolution
Learning about the phases and sequences of stellar evolution helps to understand what processes occur in the life of stars .
It is advisable to be aware of the cycle prior to the main sequence instance (period during which energy comes from nuclear fusion involving hydrogen and occurring in the stellar core).
In the premain sequence stage (a brief phase where the energy comes from the phenomenon of gravitational collapse and it is believed that the existence of circumstellar disks of considerable density ideal for planetary formation is widespread) the set of stars FU Orionis , the the Herbig Ae/Be stars and that of the T Tauri stars .
Planetary nebulae appear in the last stage of stellar evolution and have considerable relevance for the development of galaxies at a chemical level since they return various elements to the stellar medium.
In the main sequence , meanwhile, stars with a diverse range of temperatures are located, among which blue giants and red dwarfs appear. This time is characterized by the burning of hydrogen in the star 's core.
Later, the red clump phase appears (a step that, in the graph popularly called the Hertzsprung-Russell diagram, is located in the right area and above the central-inferior segment corresponding to the aforementioned main sequence), followed by the asymptotic branch giant , which is subdivided into an early giant asymptotic branch and a giant asymptotic branch with thermal pulses .
It is necessary to highlight that the old age of stars begins when hydrogen disappears from the central sector of each one of them. The mass will determine which and in what way these celestial bodies will evolve. Those whose mass is classified as low or intermediate, for example, can go through instances of subgiants and red giants , while those with high mass go through times of blue supergiants and yellow supergiants .