Where Did the Universe Come From? And Other Cosmic Questions: Our Universe, From the Quantum to the Cosmos by Chris Ferrie & Geraint Lewis
Author:Chris Ferrie & Geraint Lewis [Ferrie, Chris & Lewis, Geraint]
Language: eng
Format: epub
Tags: Space Science, Physics, science, Astrophysics, history, Cosmology
ISBN: 9781728238814
Google: M-ErzgEACAAJ
Publisher: Sourcebooks, Incorporated
Published: 2021-11-15T23:33:49.418929+00:00
Why do dying stars rip
themselves apart?
Stars burn by forging heavier elements from lighter elements. The rate at which these nuclear fires burn depends upon the conditions in the heart of a star. Simply put, the higher the density and temperature, the more rapidly elements are transmuted and the more brightly a star can shine. For an individual star, these characteristics are defined by its mass.1 The more massive a star, the more gravity can squeeze the core to higher densities and temperatures and the more energetic the stellar output.
In the smallest starsâthe ones that barely achieve the conditions to ignite their nuclear reactionsâhydrogen is converted to helium in a very sedate fashion. With a mass only about one tenth that of our Sun, these red dwarfs glow feebly but have a hundred trillion years of fuel to burn through. Once the hydrogen fuel is gone, the core of the red dwarf is too cool to burn helium into heavier elements, and the star simply blinks out, cooling and fading into the darkness.
Our Sun, being more massive, can squeeze its core harder. It could burn through its nuclear fuel in a mere ten billion years, but once the hydrogen is exhausted, a little extra squeeze can begin to burn helium into carbon and oxygen. This internal rearrangement will have a profound effect on our Sun, causing its outer layers to swell and cool. During this red giant phase of its life, the outer layers of the Sun will swell to engulf the orbits of Mercury and Venus and possibly outward to swallow the Earth and Mars. But donât worryâwe have another few billion years before this radical change begins.
Eventually, our Sun and other stars with a similar mass will exhaust their nuclear fuel. The core will become too cool, unable to burn carbon and oxygen into anything heavier. The star will undergo more internal upheaval as the fuel is depleted, pulsating as the nuclear burning becomes erratic. In the end, the outer layers of the star will be puffed off in one final sigh. While the result can be spectacularly beautiful, viewed through telescopes as planetary nebulae, they are the markers of stellar grave sites.
The life of a more massive star, several times larger than the Sun, can be yet more spectacular. The immense gravity of these large stars means the conditions at their hearts are no barrier to nuclear burning. Hydrogen is rapidly burned into helium, helium into carbon and oxygen, and then up into heavier and heavier elements. Very massive stars can churn through their nuclear fuel in a few tens of millions of years, constantly readjusting their internal structure as material created in one nuclear reaction becomes fuel for the next.
A star about ten times the mass of the Sun will spend roughly ten million years burning through the hydrogen at its core, then about one million years burning helium. Burning through carbon might only last a few hundred years, while oxygen burning might be over in a few hundred days.
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