How stars are born and die? Interpretation “Amazing” – 01/03/2022
4 min read
They seem to have always been there, but no. Not because the stars are immortal because they are in the sky. Even stars are born and die.
If the composition of these luminous stars was only one, then their life cycle could vary in billions of years. And death, in three different ways, ends worthy of an end Movie Science fiction – with explosions, mutations and black holes.
The birth of stars occurs when a giant cloud of gas and dust begins to gather in space, in a region called the “stellar nursery”.
The outer parts of this cloud begin to fall off as they condense and heat up.
Then, each of these dense parts separated from the cloud acquires more density and heat, and when it begins to rotate around itself, it turns into a kind of disk.
The gas and dust cloud Gum 15 in the constellation Vela is the birthplace and home of massive young stars
Photo: ESO
As the temperature and density of this “disk” increases, hydrogen nuclei fuse to form helium and release energy. Then begins the nuclear fusion that completes the birth of the star.
“The sun and the solar planetary system arose this way. They arose from this original gas disk,” says astrophysicist Joao Steiner, principal professor at the University of the South Pacific’s Institute of Astronomy, Geophysics and Atmospheric Sciences.
From there, the star begins to “burn the fuel” that “feeds” it throughout its life cycle. It is hydrogen – and then helium – that underpins this massive “nuclear reactor”, a veritable plant of natural light.
The life cycle of stars varies according to their size.
A star 100 times the mass of the Sun can “only” consume its fuel in a million years. The stars are ten times smaller than the Sun, on the other hand, they “live” trillions of years.
“When the fuel runs out, the core deflates and the star ends up exploding,” Steiner explains.
One life, three different deaths
When the fuel runs out—and fusion burns even heavier elements like iron—and the nuclear reactor is shut down, the star can no longer bear the weight of the layers close to its core.
Then it explodes in a phenomenon called a supernova.
However, depending on the stellar mass, this “death” occurs in different ways.
“If the mass of the star is between twenty-eight times the mass of the Sun, then the nucleus turns into a neutron cloud. And if the initial mass is twenty times greater than the mass of the Sun, then this nucleus turns into a black hole,” says the astrophysicist.
When a star has a small mass, less than eight solar masses, the explosion cannot be called a supernova. “If a star has a small mass, it also extrudes a large portion of its outer atmosphere, but in the form of a gentler breeze.”
Dying massive stars can also be optical. Classified as a planetary nebula, NGC 2392 is a star like our Sun in an advanced stage as it transforms into a red giant.
Imagem: X-ray: NASA/CXC/IAA-CSIC/N.Ruiz et al, Optical: NASA/STScI
These differences, which occur at the end of a star’s life cycle, can be explained by the “magnitude of collapse” of the outer portions of the star in its core.
In bright stars, these layers are gently expelled and transformed into a planetary nebula with a central star inside.
This then turns into a white dwarf, a dense, hot star, a kind of “corpse” made of carbon and oxygen, which has cooled for billions of years without fading out.
In larger stars, when there is a supernova, the fall of the outer parts of the star is more violent. Extremely violent in the case of stars more than 20 times the mass of the Sun, when they contract into a black hole.
Among the remaining supernovae, there are two possibilities: either there is a neutron star or there is a black hole.
“The first is something more dense than a white dwarf, in which equilibrium is maintained by pressure from a more compact substance, a neutron soup. The second is this formation without any pressure capable of maintaining mass around the center in this region. Explains Francisco Jose Jablonsky, researcher at the Institute of ENPI (National Institute for Space Research), that this formation cannot escape from it.”
Is the sun? Will you die too?
It will happen, but it will still be a few billion years, when all the hydrogen – and helium – have been burned off by their nuclear fusion.
In the process, during the combustion of helium, it will expand.
At this moment, “the Sun will reach a dimension, a ray, that will swallow up the Earth,” says Jablonsky. “you will be [estrela] Red giant. Some of the red giants have dimensions that may reach the orbit of Mars.”
Your end will not be glorious. Having become a red giant, what remains, after expelling what has expanded around the central hot zone, will be a “hot bump, white dwarf, and then gradually cool off.”
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