Stellar Evolution

After its core hydrogen is depleted, a red main sequence star will go supernova after its red giant phase.

When stars died, chemicals other than hydrogen and helium formed, which led to the next level of complexity—Heavier Chemical Element. Most stars spent about 90% of their life over billions of years on during protons and hydrogen nuclei into helium nuclei. When they run out of fuel, the furnace at the center of the star stopped supporting the star, and gravity took over. Small stars did not have much pressure at the center. They burned hydrogen slowly over billions of years at relatively low temperatures. When they died, they would slowly fade away. However, great stars had so much mass that they can create enormous pressures and temperature, and when the giant stars ran out of hydrogen, the temperature got cranked up even higher, which led the star to collapse. The high temperature that the collapse caused was able to make helium nuclei fuse into nuclei of carbon. When a star used up its helium, it collapsed again, and the cycle started over. The star heated up and began to fuse carbon to form

- Because the interior of a less massive star doesn’t reach sufficiently high temperature and pressure to fuse helium. So the only energy source is hydrogen.

As the star begins to run out of hydrogen fuel the core inside the star begins to collapse while rising in temperature, which causes the core to heat up rapidly pushing the outer layers of the star outward causing them to expand and cool the star is now a red giant. Average stars like our sun will have a relatively peaceful ending toward the end of their red giant phase. The star begins to pulsate releasing its outer layers resulting in solar winds, as these layers begin to drift away only the core remains, this is considered a white dwarf. Eventually the white dwarf will consume all its energy after this happens it will become a cold black dwarf. Massive stars come to an end much differently, after the high mass star runs out of fuel the outer layers of the star begin to collapse upon the core, and then are released in a massive explosion into the cosmos this is called a supernova. After, either a neutron star or a black hole remains these are vastly different a neutron star is an incredibly dense object made up of sub-atomic particles called

The star starts off as a nebula. (Along with every other star). From there, the star would become a protostar. Following the smaller sized star would become a Red Dwarf star. When the star is in this stage, it is in its main sequence and will stay in this stage for a very long time. As time passes the star will begin to become a Red Giant. After this stage in the star’s life, the star will begin to cool down, and become a white dwarf. From the white dwarf stage, the star will be coming to an end. The final stage will come to the black dwarf stage where it would be there for a very very long

At that point, the star begins to fuse helium into carbon in the core. This is called helium fusion. In order for this to happen, the core’s density has to increase and the temperature has to reach about 100 million Kelvin. However, a complication arises when helium fusion begins. The star’s core is degenerated and the burning becomes unstable since the core is not able to accommodate the fusion. The increase of internal pressure and temperature caused by the burning of the helium leads to an astronomical increase in outward pressure. This is, eventually, able to regulate and the core is able to expand and decrease its

Stars like our Sun, which are no more than 1.44 solar masses, will undergo fusion of hydrogen into helium. Over its life time the star slowly uses its supply of hydrogen by fusing it into helium. These reactions require high temperatures. Eventually the star will completely fuse hydrogen into helium in its core leaving inadequate amounts of thermal pressure to balance gravity. This will cause the centre of the star to contract to compensate for the heat energy lost.

Stage 8 is when the star starts to run out of fuel. It has spent close to 10 billion years burning hydrogen in its core and now it’s starting to run low and almost empty of the fuel it requires to keep burning. As the hydrogen starts to run low, helium levels start to increase in the higher temperature core as well as on the surface. However, the surface helium isn’t as noticeable because it doesn’t burn as high or fast as the inner core. But as the hydrogen completely runs out, the nuclear fusion subsides and a core of non-burning helium grows, forcing the burning of the star to head out of the inner core and up to the outer core. At this point, the radius of the star starts to grow rapidly because of the gas pressure and the core shrinks under the pressure of gravity.

If the fusion of hydrogen into helium of red dwarfs’ was any less they would not be classified as a red dwarf at all. Instead, they would be brown dwarfs which are not stars since they cannot sustain hydrogen fusion. More massive stars accumulate hydrogen and helium in their cores while red dwarfs are convective. This means the helium and hydrogen are constantly mixing throughout the entire mass of the of a red dwarf

have greater gravity. To keep the star from collapsing, the star must fuse more hydrogen atoms to

It is a large bright star with a cool surface. Just like the Sun, it eventually runs out of hydrogen fuel at its center. Red Giants have a diameter of about 10 to 100 times the size of the Sun. The reason for why the Red Giants are so bright is because of its size, although there surface temperature is less hot than the Sun’s. If you were to measure the temperature, it would be about 2000 to 3000oC. Red Giants, very large stars, are also often called SuperGiants. These stars sometimes have diameter of up to 1000 times the size of the Sun, also having more than 1 000 000 times the luminosities of the Sun (Life cycle). These stars live for only a few thousand years to 1 billion years. Eventually the helium in the core runs out and fusion stops. The star shrinks until a new helium shell reaches the

Stars generate energy via nuclear fusion of elements. Stars of the magnitude great enough to become type II supernovae possess the mass needed to fuse elements that have an atomic mass greater than hydrogen and helium. The energy generated by these fusion reactions is large enough that it is able to counter the force of gravity and prevent the star from collapsing, maintaining stellar equilibrium. The helium produced in the core builds

The life cycle of the Sun starts like all stars with a cloud of dust and gas made up of mostly hydrogen. If the cloud cools, it will shrink because of the gravitational pull between the particles

After a time, the hydrogen runs out almost completely, and it collapses. New reactions begin to take place in the core and these reactions cause the star to expand rapidly. As the stars begin to deplete their new fuel, they switch to others. New elements are formed in the cores of stars but they become too heavy. The star has reached its end growth. When it reaches the end, a tremendous amount of energy is released and it begins to shed its outer layers, the gravity is too weak hold onto them anymore. Once the layers are removed, in the stars place is a fiery core called a planetary nebula. Eventually, the core runs out of fuel and it collapses. This star is now in a very dense state, and is called a white dwarf. Eventually, the white dwarf cools until it no longer shines. This dead star is called a brown dwarf.More massive stars, however, have more violent ways of dying. Some stars turn it into a supergiant. Supergiant stars are extremely bright, and are extremely large. Supergiant stars cores, can collapse violently and suddenly. This collapse causes a tremendous explosion, called a

Main sequence stars like our own sun enduring in a state of nuclear fusion during which they will produce energy for billions of years by replacing hydrogen to helium. Stars change over billions of years. When their main sequence phase ends they pass through other states of existence according to their size and other characteristics. The larger a star's mass, the shorter its lifespan is. As stars move toward the end of their lives, much of their hydrogen will be converted to helium. Helium sinks to the star's core and raises the star's temperature—causing its outer shell to expand. These large, puffy stars are known as Red Giants. The red giant phase is actually a prelude to a star shedding its outer layers and becoming a small, dense body called a White Dwarf. White dwarfs cool down for billions and billions of years, until they finally go dark and produce no energy at all. Once this happens, scientists have yet to observe, such stars become known as Black Dwarfs. A few stars avoid this evolutionary path and instead go out with a bang, exploding as Supernovae. These violent explosions leave behind a small core that will then turn into something called a Neutron Star or even, if the remainder is large enough, it is then turned into something called a Black Hole.