Friday, February 14, 2014

How Stars are Born

The atoms that make up our world, and even our bodies, came from the inside of a star. These atoms were formed in the centers of stars and spewed out into the universe with the violent death of these stars. So it seems natural to wonder that if we come from stars, where do stars come from?

All stars are born in nebulae. Nebulae are enormous clouds of dust and gases, mainly hydrogen and helium found in galaxies. Nebulae contain the remains of dead stars and along with gas created in the Big Bang itself. Some nebulae, called planetary nebulae, come from stars similar to our sun that died and released their mass out into space. Others formed from violent supernovae that spewed matter out over vast amounts of space. 

The famous "Pillars of Creation" observed by the Hubble
Space Telescope, a part of the Eagle Nebula which lies
7000 light years away from our Solar System.
Some parts of nebulae are slightly denser than others. Over millions of years, the gas and dust are pulled together into these denser knots by their own gravitational attraction. As the center becomes denser, it gets hotter and the core becomes known as a protostar. This protostar pulls in more and more dust and gas and when it reaches a temperature at or above approximately 10 million degrees Kelvin it begins thermonuclear fusion. The protons of hydrogen atoms are fused together to make helium and helium is fused with hydrogen to make other, heavier “metals”. This process gives the star enough energy to support its mass from collapsing in on itself and to produce the light that makes it shine. If a protostar cannot gain enough heat to begin thermonuclear fusion, it will either collapse in on itself or dissipate outwards and fail to become a star. Once a star begins this process it takes in more and more mass until it reaches a size it can maintain with the amount of energy it produces. It has now become a mature star. The majority of the remaining clouds of dust around the star are blown away by stellar winds, but some may eventually become planets and asteroids.

Stars form to be different sizes. Average stars, like our Sun, have average lifespans of several billion years. Once they have burned through the hydrogen in their core their mass will expand out into space in a planetary nebula. Huge stars, called giants and supergiants, have short lifespans. These gigantic O stars live for only a few million years, compared to our Sun’s 10 billion year lifespan. They burn through the hydrogen in their core quickly and then can no longer produce the energy needed to keep them from collapsing in on themselves. Sometimes these stars have so much mass that they collapse in on themselves and then explode out into space in a supernova shooting out the elements they fused in their core during their lifetime. 

With the death of old stars, new nebulae are formed and the cycle of death and rebirth begins once more. New stars will form from the dust of the old ones many with their own solar system of planets and asteroids revolving around them. One could possibly have a planet orbiting it with conditions remarkably similar to our own Earth.
Clare Isaacson