star life cycle

The stars also respect the cycle of life, they are born, live and then die. But do you know how they come into being or how they die out?

In our galaxy alone, there are between 100 and 400 billion stars, The Milky Way. Some are at the end of their lives as Betelgeuseothers are in full age, such as the sun and finally there are those which have not yet seen the light of day, or which are just now in full formation.

The birth and life of stars

all starswith very few exceptions, find their origin in interstellar clouds of gas and dust: the nebulae. During a process that can last several millions, even billions of years, the elements come together thanks to gravity and pull the nebula together until it fragments into several celestial bodies different which will first give birth of protostellar bodies or protostars. It corresponds to the embryonic stage in humans.

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NGC 3372, or the Carina Nebula, captured in 1999 by the Hubble Space Telescope. It lies 7500 light years from Earth. It is in these clouds that stars are born. NASA/GETTY_IMAGES

At this stage, their core is not yet hot enoughto induce nuclear fusion reactions and allow them to emit energy and light. The more the protostars will gain mass, the more their core will be heated until they reach a temperature of 15 million kelvin and allow fusion between hydrogen and helium, the gases that make it up. The star therefore enters the “main phase” of its life. Radiation and nuclear reactions originating in their core will maintain their gravity. The stars will therefore not be able to collapse in on themselves. The stars will then shine with a thousand lights for millions or even billions of years until their fuel runs out. As is the case with the Sun, born 4.6 billion years ago after causing the solar nebula to collapse on him. And it must at least continue to shine 5 billion years before they die out.

The death of the stars

After using up all the hydrogen which held their heart in place, the gravitational force of the latter will also be depleted. Thusthe inner layers of stars and their cores will begin to collapse in on themselves when the outer layers will move further and further away to form stars up to 100 times larger than their original size. So they will be red giants as arcades in the constellation Bouvier or the red supergiants if they are massive stars like Betelgeuse in the constellation Orion.

At this stage, there are two optionswhich is conditioned by the mass of the star.

medium stars

A star is considered to be medium size when it reaches a mass that can be up to seven times that of the Sun. After its transformation into a red giant, the core of the star is still hot enough to helium fuses to carbon. So when the remnants of helium have been consumed, the material that makes up the star will be rejected all the way around the star to form one planetary nebula. At its center will then be what remains of the star, a very dense, shiny ball: a white dwarf.

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NGC 7293 or the Helix Nebula is a planetary nebula located 694 light years from Earth. It is also nicknamed “God’s Eye”. In the center is a white dwarf. NASA/GETTY_IMAGES

The massive stars

Stars that greatly exceed seven solar masses considered to be massive starsand their death is much more spectacular and catastrophic than their smaller counterpart. After reaching the stage of red supergiant, the core will fuse helium into carbon just like in the smaller ones, but it doesn’t stop there. As the helium runs out, it will contract even more, becoming denser and hotter until it produces iron atoms. Then follows a losing battle against gravity that will cause the heart of the star to collapse in on itself.. Its core will then be ejected in a giant explosion: a supernova, and the gases and dust that made it up will be ejected to its galaxy. Then there is nothing left.

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Artist’s impression of a supernova. Science Photo Library – Mehau Kulyk/GETTY_IMAGES

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