it’s the life of a star
Who has never tried to count the stars in the sky? Hundreds, thousands, millions… Counting them is an impossible task, we already told you. However, although it may seem that this infinite number is constant and that the number of luminous points in the sky does not change, this is not so: old stars disappear, and new ones take up places that were previously empty. In other words, so do the stars are born and diewhich makes the sky we see at night very variable.
In fact, between birth and death stars live different phases, evolving from one to another and changing characteristics as important as its physical form or composition. Does a stellar nebula, white dwarf, or supernova sound familiar to you? Well, they all represent different moments that a star can go through.
STAR FORMATION
But let’s start from the very beginning: the birth of a star. This is a process that begins in the gas and dust clouds of the interstellar medium, known as nebulae. These clouds, composed primarily of hydrogen and helium, as well as traces of other heavier elements, provide the material needed for the birth of a star. violation the initial “push”. This must be a cosmic disturbance caused by a supernova explosion or the passage of a shock wave, which, due to its magnitude, reaches compress dust and gasincreasing density and causing the formation of gravitational cores.
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As these nuclei collapse under their own weight, protoplanetary disk around this nascent star – that is, a ring of heavy materials orbiting the core of the collapsing star. Temperature and pressure at the center of the disk gradually increasereaching a level sufficient to trigger nuclear fusion and therefore officially marking the birth of a new star.
During this period, the star is in the so-called Hayashi sequence, where its energy is generated mainly due to gravitational compression. However, over time the star will reach balancecounteracting the force of gravity with pressure created by the energy released from its core.
Tarantula Nebula.
MAIN SEQUENCE
Thus, as soon as the star loses this instability, it enters main sequencethat is, the most balanced and longest phase of your life, where most of your existence is spent in harmony between gravity, which tends to destroy the star, and internal pressure created by nuclear fusion in the core. At this stage the star turns hydrogen into helium through nuclear fusion, releasing energy that provides the heat and light that makes the star shine.
The smallest stars such as red dwarfs, can remain on the main sequence for billions of years because they burn hydrogen much more slowly than more massive stars. On the other hand, the latter, more dense and massive, like blue giantshave shorter main sequence lifespans because they burn their nuclear fuel much faster.
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However, no matter what star it is, they all experience subtle changes in their internal structure and surface brightness while in this phase as they move towards gradual exhaustion its nuclear hydrogen. These changes can manifest themselves in changes in their surface temperature, visible luminosity and other number of identifying parameters.
Diagram of main sequence stars.
EVOLUTION AND STAR DEATH
For low- and intermediate-mass stars like our Sun, the residence time on the main sequence is almost 10 billion years – The Sun has been in this phase for 4.5 billion years and is expected to remain there for another 4.5 billion years. However, as their hydrogen depletes, these types of stars often expand to become red giants, releasing their outer layers into space, forming nebulae, and eventually becoming white dwarfscold, dense remains that slowly freeze over time.
On the other hand, massive stars, whose mass is several times the mass of the Sun, have shorter lives and evolve much faster. violent and explosive. Thus, they burn hydrogen much faster, depleting their nuclear fuel in just a few seconds. several million years.
After leaving the main sequence, these stars can experience catastrophic events such as explosions supernovaewhich eject enormous amounts of energy and material into space, enriching the interstellar medium with heavy elements formed in the nuclear reactions of an already dying star.