23 Mar 2015
When we look in the sky at night and see all the stars your eyes can see. We think they are permanent although we may think this technology has given us the chance to see otherwise. Massive telescopes like the Hubble space telescope has let us experience and see the birth and death of stars. Where some stars just burn out and fade away other stars go out with a bang. There are billions upon billions of starts in space and their all different sizes. But only one type of star will collapse in and turn its self into a black hole.
Let's start from the beginning, the pillars of creation is a piece of a space nebula 7,000 light years away from earth in the eagle nebula it is just one of the billion birth places of stars. What are they made up of well I'll tell you they are made up of dust gas and different elements of the periodic table like hydrogen, helium, calcium oxygen silicone and iron.
As gravity forces this dust and gas mixture into a flat disc accretion occurs, a process in which more atoms are added to create a protostar. Now at this stage a star is not yet stable because of the countless reactions occurring within the forming star. For this newly forming star to become stable it must reach equilibrium. Equilibrium is the balancing act between the star and gravity. Equilibrium occurs by gas pressure equaling the force of gravity. Gas pressure occurs by thermonuclear fusion which is the combining of the nuclei of small atoms to form the nuclei of larger ones, with a resulting release of large quantities of energy. For nuclear fusion to begin and equilibrium to occur the core of a protostar has to reach 18 million degrees Fahrenheit. When it reaches this critical temperature it will begin nuclear fusion of hydrogen into helium. And if nuclear fusion doesn't happen it will end up a brown dwarf. Once nuclear fusion begins a star is born.
Main sequence star:
A main sequence star is made up of essentially two sections the core where nuclear fusion occurs and the outer gaseous shell. Stars will live out most of their life in the main sequence just as our sun is. Once a star begins nuclear fusion it becomes self luminous it generates its own heat. Now how long will a star live out its life well that's hard to tell it all depends on the stars mass and it turns out that how hot a star is will determine the color of the star like for instance a red dwarf star which is ½ to 1/10 the mass of our sun. With its surface temperature less than 7,000 degrees Fahrenheit and is also the most common type of star in the universe. However we don't see the small Red stars we see the massive blue main sequence star, its surface temperature is 45,000 degrees Fahrenheit, it is up to 20 times the mass of the sun and up to 10,000 times more luminous than that of our sun. There is however a down side to being a massive blue star. With that being said the less the mass of a star the less atoms a star has to maintain its equilibrium. The bigger the mass of a star the more atoms a star will have to maintain its equilibrium. With regards to a stars life however the more massive a star the shorter its life will be and the less massive a star the longer it's life. This is because in larger stars thermonuclear fusion happens at a much faster rate than that of a smaller star. Once a star has reached equilibrium it has not stopped changing there just isn't a huge amount of change going on, and as we already know a star will live out most of its life in this stage. But we must remember gravity forced the star together to begin with and it also wants to destroy it.
The beginning of the end:
Once a star has run out of hydrogen to convert to helium, the star will begin to contract so that it can begin to convert helium to carbon so that the star can continue to hold up its equilibrium. For a star to convert helium the internal temperature of the star must reach an astounding 180 million degrees Fahrenheit. at this point the star has now become a red giant or red super giant. As gravity causes the core to contract helium will begin to burn in the core. But rapid hydrogen reactions occur faster in the outer layers of the star. As the temperature of the shell increases the outer layers will begin to swell and expand. Since fusion is releasing more energy in the helium burning stage than in the main sequence the star is a lot less stable. As the star begins to run out of helium it will again contract to convert helium to carbon and oxygen into neon then, magnesium, silicone, sulfur and then iron. As massive stars come to the end of their life it begins to look like an onion in cross section with the outer layer being hydrogen and the inside being layer after lay after layer of heavier elements. As the massive star tries to convert iron it fails because iron being the stable of all nuclei absorbs energy instead of releasing it. When fusion decreases temperature will also decrease. And the rate of the star collapse increases. As the iron core builds up in the star and gravity contracts it even further the iron core will rebound and smash through the outer layers of the sun kicking of a type 2 super nova. The only thing left of the star is the core left completely intact. Gravity still not giving up on destroying this star will contract it even further and force this core of a star to convert electrons to neutrons only one problem neutrons don't like to be near each other. So now you have a new stable object even smaller and denser. This compact star core becomes a rapid whirling ball of neutrons. Which give the star the name neutron star as gravity compacts this neutron star even further and if at the last moments of the neutron stars death enough matter falls in to its core it will collapse into itself and form a black hole in which nothing escapes not even light.
So let's recap we have talked about gravity forcing dust and gas together to form a protostar. Also how nuclear fusion is what makes a star a star and for that to happen the core must reach 18 million degrees Fahrenheit. We also went over that as soon as nuclear fusion begins a star is born. As a star comes to the main sequence it will live here for most of its life. But as soon as the star runs out of hydrogen gravity will contract it until it reaches an internal temperature of 180 million degrees Fahrenheit and will burn helium to keep its equilibrium. The sun will also convert carbon and oxygen into neon then, magnesium, silicone, sulfur and then iron trying to fight off gravities crushing force. But it doesn't happen and the iron core in the star will rebound sending of shock waves causing a type 2 supernova. Leaving the left over core intact and allowing gravity to take over again gravity will force the electrons left over in the core to neutrons and now we have a neutron star that gravity will compress and if enough matter falls in the core it will eventually collapse in on itself and form a black hole.
All information I used in this speech came from the history channels The Universe Life and death of a star. Season 1 episode 10 and also form http://sunshine.chpc.utah.edu life cycle of a star.
Picture of brown dwarf star form http://news.discovery.com/space/rogue-brown-dwarf-lurks-in-our-cosmic-neighborhood.html
Picture of Red super giant form http://www.nasa.gov/multimedia/imagegallery/image_feature_784.html
Picture of black hole destroying to stars if an artist's enactments of the destruction of a black hole picture form http://www.cosmographica.com title Don Dixon space art.
All other pictures seen here today were from Hubble space telescope http://hubblesite.org
I would like to thank all of you for taking the time to listen to my speech on a stars life and death. Enjoy the rest of your day.
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