Stellar Evolution

In its next main stage of stellar evolution, the Sun is expected to enter the red giant phase. As it exhausts hydrogen in its core, the core will contract and heat up, causing the outer layers to expand significantly. This expansion will ultimately engulf the inner planets, including Mercury and Venus, and possibly Earth. Eventually, the Sun will shed its outer layers, leaving behind a white dwarf surrounded by a planetary nebula.

In the sun it is just protons, which are hydrogen nuclei. On earth experiments are using two isotopes of hydrogen, deuterium and tritium. These are still the same element, hydrogen, just two different isotopes.

Because the larger mass means more core pressure, making fuel (hydrogen turning into helium) burn faster and more frequently, resulting in a hotter, brigher star. A small mass star has less fuel and internal pressure, so it generates less light and is red in color. A medium star like our sun burns moderately, and is yellow.

The H-R Diagram places these stars in spectral classes, from biggest and hottest to smallest and dimmest, and the orders are O, B, A, F, G, K and M. We are a type G star.

Think of a fire; the more fuel you put on it, the hotter and brighter it blazes and it can become white-hot if it is a very intense fire. As the ashes burn down, the fire is smaller, dimmer and the coals appear red, which is cooler.

The principle is the same with stars; the bigger and hotter they are, the brighter they burn but they have shorter lives than do moderate and small stars.

When a collapsed core becomes so dense, it reaches a state known as neutron degeneracy, where neutrons can exist in close proximity due to the exclusion principle preventing them from occupying the same quantum states. This forms a neutron star, where the core is primarily composed of densely packed neutrons.

Starch is made up of three elements: carbon, hydrogen, and oxygen. These elements are not directly derived from the sun, as starch is synthesized by plants through photosynthesis using carbon dioxide from the air, water from the soil, and sunlight energy.

Nuclear fission. It realeases nuclear energy by spitting big atomic nuclei, usually those of uranium. Neutrons are fired at the nuclei. As the neutrons smash into the nuclei they split off more neutrons, which bombard other nuclei, setting of a chain reaction, which makes energy.

The apparent visual magnitude of Beta Herculis is 2.81. It has been known since 1899 that it is in fact a binary star, and modern measurements (including satellite telescope) have resolved the motions and apparent sizes of the two bodies.

Massive stars cannot generate energy from iron fusion because iron fusion does not release energy, rather it absorbs energy. Iron is the most stable element, and fusion of iron requires more energy than it produces, making it an unfavorable process for generating energy in stars. This leads to the collapse of the star's core and triggers a supernova explosion.

If a gamma ray burst hit Earth, it could potentially strip away the ozone layer, leading to an increase in harmful ultraviolet radiation from the sun. This could have catastrophic effects on the environment and life on Earth. However, the likelihood of a gamma ray burst hitting Earth directly is very low.

The remnant core of a star that becomes a supernova will normally be a neutron star, or possibly a pulsar (a rapidly spinning neutron star). The largest of stars would theoretically create a black hole, a singularity containing all of the core's mass at a single point and preventing even light from escaping its massive gravity.

The rapid collapse of the star compresses atoms together and may cause nuclear fusion and make heavier elements.

Thermonuclear fusion is still going on in the core of a red giant, but it is a different type of thermonuclear fusion. The center of the core has reached high enough temperature and pressure that it can now burn helium, producing carbon.

3 4He --> 12C

The large amount of energy released by this type of fusion pushes the outer layers away, making a giant star. The expansion of volume of the surface layer causes it to cool, appearing red. Thus a red giant.

they study the stars the same reason we study most things, to understand.

relly? they studly them because space may hold the awnser to our meaning, how we were created, and how we will end.

The corona is hotter than the photosphere because the sun's magnetic field carries energy upward from the surface and into the chromosphere and corona. The opposite effect is observed when the magnetic fields cause sunspots to form resulting in cooler surfaces.

Our Sun is currently on the Main Sequence stage of it's evolution.

As a G-type star fuses its hydrogen to helium, this helium will gather in the core. As a result, the core will contract under its own weight as hydrogen is being spent. The contraction causes an increased hydrogen fusion rate, increasing the temperature. When insufficient hydrogen remains in the core, the layers above are no longer supported by the outward pressure of radiation, and collapse on top of the core, causing it to contract further, and also initiating hydrogen fusion outside the core. At this point, the star leaves the main sequence, and becomes a red giant. At this stage, the core of the giant may reach critical density for helium fusion to initiate. Since the core is composed of mostly degenerate matter at this stage, there is no regulation of the fusion rate. Also, degenerate matter is less opaque to the energies produced than non-degenerate matter, so conducts them better.

Ehr, to summarize: the helium flash occurs during the red giant stage of G-type stars.

Stars form when enough hydrogen accumulates to cause enough internal pressure and heat to make the ball of hydrogen glow from the fusion of hydrogen to form helium. Depending on the size and temperature of the new star, it will fall along the HR Diagram as a class O,B,A,F,G,K or M star. Class O stars are very big and very hot, giving off blue/white light. Class M stars are small, cool red dwarf stars. Our sun is a class G star, a small star which burns moderately and is yellow.

Depending on the mass of the star, it will burn at different rates. Class O and B stars, although large, burn very fast because they are so hot. Class M stars, being small and cool, can burn for many millions of years longer.

Eventually, all stars run out of fuel and begin to collapse on themselves. What happens next depends on the type of star.

Large, hot stars will explode in a supernova, ejecting their entire blanket of gases into space and leaving behind a small core which will be a pulsar (neutron star), or even a black hole.

Medium stars like our sun will swell their outer layers to become Red Giants (such as Betelguese in Orion). This phase will last for a few million years until the core finally cannot support the outer layers any longer. To give you an idea of size, our sun will eventually send it's outer layers as far out as to engulf Mars.

Once these moderate Red Giants run out of fuel, they collapse and form a white dwarf star, which will be the end result of our sun. After billions of years, they will cease to glow and become black dwarfs. (Do not confuse this with black holes..completely different).

Small red dwarf stars will puff out outer layers in a planetary nebula, but will not have enough energy to explode. They will eventually become small black dwarf stars as they lose their energy and can no longer burn.

This is very brief because this is a very complex process, but I hope this helped.

White dwarf stage. Note that not all stars reach this stage. Some stars experience runaway criticality and go supernova. Also, white dwarf stars in binary systems can still go nova if they are acquiring hydrogen from their partner.