HaWaIiAn CoMpAsS
StArS
Tuesday, November 18, 2008
The Hydrogen Burning Stage
The proton-proton reaction occurs during a period called the hydrogen- burning state, and its length depends on the star's weight. In heavy stars, the great amount of weight puts a large amount of pressure on the core, raising the temperature and speeding up the fusion process. These heavy stars are very bright, but only live for a short amount of time. After the energy from this deuteron-hydrogen fusion process ends, the star begins to contract again, and the temperature and pressure subsequently increase. Nuclear fusion occurs between the hydrogen and lithium & other light metals in the star, but this process soon ends. Contractions starts again, and the extreme high temperature and pressure cause the hydrogen to transform into helium through the carbon-nitrogen-oxygen cycle. When all the hydrogen has been used up, the star is at its largest size, and it is called a red giant. Different things can happen to the star now.
The birth of a star
In space, there exists huge clouds of gas and dust. these clouds consist of hydrogen and helium, and are the birthplaces of the new stars. Gravity causes these clouds to shrink and become warmer. The body starts to collapse under its own gravity, and the temperature inside rises. After the temperature reaches several thousand degrees, the hydrogen molecules are ionized (electrons are stripped from them), and they become single protons. The contraction of the gas and the rise in temperature continue until the temperature of the star reaches about 10,000,000 degrees Celsius (18,000,000 degrees Fahrenheit). At this point, Nuclear fusion occurs in a process called proton-proton reaction. Briefly, proton-proton reaction is when four protons join together and two are converted into neutrons; an 4He nucleus is formed. During this process, some matter is lost and converted to energy as dictated by Einstein's equation. At this point, the star stops collapsing because the outward force of heat balances the gravity.
Thursday, November 6, 2008
Star life and death
Star Life & Death
Honestly, the life of a star is fairly boring. It fights gravitational collapse for several million to several billion years (depending on the mass) by fusing atoms together. The energy the star gains by fusing these atoms keeps it from collapsing. If a star is massive enough, it will fuse heavier and heavier atoms -- hydrogen to heluim, heluim to carbon, carbon to ... until ... elements are fused into iron. Fusing iron to form heavier elements actually requires energy, so the star would not gain anything by continuing fusion of iron atoms.
Most of the star's life is spent fusing hydrogen into helium. Our sun has been doing this for some five billion years, and is expected to continue doing it for another five billion or so years. This hydrogen burning starts from the very center of the star, and moves its way out, leaving a core of helium behind.
Low Mass Stars
If the star is small enough (much less than the mass of our Sun), it never gets beyond hydrogen burning. This is because its central temperature never gets high enough to start fusing helium into carbon. Once such a star has used up most of its hydrogen, it will begin to cool and collapse into a "brown dwarf".
Intermediate Mass Stars
Stars with masses close to that of our Sun (up to about five times the mass of our Sun) will experience helium-to-carbon burning in their cores. Outside the helium core, hydrogen will continue burning into helium.
At this point, the outer layers of the star will expand to conserve energy -- the star swells, becoming brighter and cooler. This is called the red giant phase of the star. The red giant loses many of its outer layers because of the radiation coming from the core blows it away. Eventually the star will cool down so much that the carbon burning stops. Such a star will collapse into a white dwarf.
High Mass Stars
High mass stars end their lives spectacularly. They, too, go through a stage where they swell up, though they swell even more than their lower-mass counterparts. This stage is called the red supergiant phase. These stars are so large that their central temperature becomes high enough that further burning in their core will occur. Eventually, they have so many layers, that they may look like an onion -- see figure below.
Image depicting 'onion' layers of nuclear burning in a high mass star
This process necessarily ends when the core has been fused into iron. Once this occurs, the core no longer has any resistance to gravity -- the core collapses. During this core collapse, the outer layers of the star are blown off in a supernova explosion. The core collapses either into a neutron star or into a black hole.
Neutron Stars
During the core collapse of the stars with masses between 15 and 30 times that of our Sun, the electrons and neutrons in the core combine into neutrons. Usually neutrons will decay into a proton and electron quickly; however, when the density of protons and electrons is high enough, it becomes less adventageous for a neutron to decay. This mass of neutrons will collapse as much as they can without violating the "no two objects can occupy the same space" law of physics (the Pauli exclusion principle).
Neutron stars are about 10 km (6 miles!) in diameter with a mass of about one and a half times that of our Sun. This makes for a huge density!
Black Holes
Exactly how black holes form is still a bit of a mystery. A neutron star can not hold itself up against gravity if it has more mass than three of our Suns. So, if the core of a massive star at the end of its life has more mass than three Suns, the core collapses into a singularity, called a black hole. Mathematically, a singularity is a point of infinite density -- a point where an finite amount of mass is squished into zero volume. Astrophysicists and physicists don't like infinities, so are still debating what exactly this means in the "real Universe".
The Sources section deals more with black holes and properties that we can infer about them from high energy observations.
Honestly, the life of a star is fairly boring. It fights gravitational collapse for several million to several billion years (depending on the mass) by fusing atoms together. The energy the star gains by fusing these atoms keeps it from collapsing. If a star is massive enough, it will fuse heavier and heavier atoms -- hydrogen to heluim, heluim to carbon, carbon to ... until ... elements are fused into iron. Fusing iron to form heavier elements actually requires energy, so the star would not gain anything by continuing fusion of iron atoms.
Most of the star's life is spent fusing hydrogen into helium. Our sun has been doing this for some five billion years, and is expected to continue doing it for another five billion or so years. This hydrogen burning starts from the very center of the star, and moves its way out, leaving a core of helium behind.
Low Mass Stars
If the star is small enough (much less than the mass of our Sun), it never gets beyond hydrogen burning. This is because its central temperature never gets high enough to start fusing helium into carbon. Once such a star has used up most of its hydrogen, it will begin to cool and collapse into a "brown dwarf".
Intermediate Mass Stars
Stars with masses close to that of our Sun (up to about five times the mass of our Sun) will experience helium-to-carbon burning in their cores. Outside the helium core, hydrogen will continue burning into helium.
At this point, the outer layers of the star will expand to conserve energy -- the star swells, becoming brighter and cooler. This is called the red giant phase of the star. The red giant loses many of its outer layers because of the radiation coming from the core blows it away. Eventually the star will cool down so much that the carbon burning stops. Such a star will collapse into a white dwarf.
High Mass Stars
High mass stars end their lives spectacularly. They, too, go through a stage where they swell up, though they swell even more than their lower-mass counterparts. This stage is called the red supergiant phase. These stars are so large that their central temperature becomes high enough that further burning in their core will occur. Eventually, they have so many layers, that they may look like an onion -- see figure below.
Image depicting 'onion' layers of nuclear burning in a high mass star
This process necessarily ends when the core has been fused into iron. Once this occurs, the core no longer has any resistance to gravity -- the core collapses. During this core collapse, the outer layers of the star are blown off in a supernova explosion. The core collapses either into a neutron star or into a black hole.
Neutron Stars
During the core collapse of the stars with masses between 15 and 30 times that of our Sun, the electrons and neutrons in the core combine into neutrons. Usually neutrons will decay into a proton and electron quickly; however, when the density of protons and electrons is high enough, it becomes less adventageous for a neutron to decay. This mass of neutrons will collapse as much as they can without violating the "no two objects can occupy the same space" law of physics (the Pauli exclusion principle).
Neutron stars are about 10 km (6 miles!) in diameter with a mass of about one and a half times that of our Sun. This makes for a huge density!
Black Holes
Exactly how black holes form is still a bit of a mystery. A neutron star can not hold itself up against gravity if it has more mass than three of our Suns. So, if the core of a massive star at the end of its life has more mass than three Suns, the core collapses into a singularity, called a black hole. Mathematically, a singularity is a point of infinite density -- a point where an finite amount of mass is squished into zero volume. Astrophysicists and physicists don't like infinities, so are still debating what exactly this means in the "real Universe".
The Sources section deals more with black holes and properties that we can infer about them from high energy observations.
Wednesday, October 29, 2008
What does Na Hoku mean?
Na Hoku Means the stars. I am doing a project on the stars to see how my ancestors used the stars to guide them where ever they were going. The Hawaiians used the stars also for telling when it is Makahiki the way to tell is when the big dipper comes and is showing. I want to be able to tell other people how the Hawaiians used them and how they can use them also. I want to be able to keep the Hawaiian culture up because you don't really see that much Hawaiians using the stars for guidance. I want to be able to teach other people about my Hawaiian culture and show how Hawaiians were in the olden days. People need to see that Hawaiians are not weaird and are really actually smart because they came up with a way to come up with time not like other people they came up with clocks and stuff to tell you what time it is but the Hawaiians were smart enough to come up with the telling time with stars.
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