There are millions and billions on stars in our universe each with its own life cycle:
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Nebula:
All stars start from a nebula. A nebula is a ball of gas (hydrogen) and dust found in space, whose gravitational attraction causes it to contract. There are 5 different types of nebula. These are emission nebulae, reflection nebulae, dark nebulae, planetary nebulae, and supernova remnants. Most nebulae are composed of about 90% hydrogen, 10% helium, and 0.1% heavy elements such as carbon, nitrogen, magnesium, potassium, calcium, iron. These clouds of matter are also quite large, being among the largest objects in the galaxy.
All stars start from a nebula. A nebula is a ball of gas (hydrogen) and dust found in space, whose gravitational attraction causes it to contract. There are 5 different types of nebula. These are emission nebulae, reflection nebulae, dark nebulae, planetary nebulae, and supernova remnants. Most nebulae are composed of about 90% hydrogen, 10% helium, and 0.1% heavy elements such as carbon, nitrogen, magnesium, potassium, calcium, iron. These clouds of matter are also quite large, being among the largest objects in the galaxy.
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Protostar:
The matter from the nebula then merges into a dense region called a protostar. As the protostar continues to condense, it heats up. Contraction of the gases causes the temperature to reach 10000 degrees K. Eventually, the hydrogen inside the protostar undergoes nuclear fusion to form helium and the star begins to shine.
The matter from the nebula then merges into a dense region called a protostar. As the protostar continues to condense, it heats up. Contraction of the gases causes the temperature to reach 10000 degrees K. Eventually, the hydrogen inside the protostar undergoes nuclear fusion to form helium and the star begins to shine.
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A Very Large Star:
The life span of a star depends on its size. Very large, massive stars burn their fuel much faster than smaller stars. If the star is a very large star, then the hydrogen is quickly used up by nuclear fusion. The core begins to contracts while the outer layers expand. The surface temperature of the star decreases. This process may take only a few hundred thousand years. _
A Super Giant:
The next stage for a very large star is becoming a super-giant. Super-giants are stars with between 10 and 70 solar masses. The large star will expand many times bigger than itself into a massive super-giant. The star will then continue to use up what is left of its hydrogen via nuclear fusion. _
Supernova:
The next step of a super-giant’s life is the supernova. This is where the pressure of the nuclear reaction inside the star is not strong enough to equalize the force of gravity and the star collapses on itself. The outer layers are then blown off in a large violent explosion and the core material of the star contracts. The remnants are more than 1.44 times the size of our Sun. The last supernova to happen in our galaxy was Kepler's star in 1604. _
Pulsar:
The next step on from a supernova is a pulsar. A pulsar is when the material from a supernova contracts and begins to emit x-rays. Depending on its size, a pulsar can either become a neutron star or a black hole. If the mass of the pulsar is less than 3 solar masses, it becomes a neutron star. A neutron star is formed after a supernova explosion blows off the outer layers of a super-giant star into a beautiful supernova remnant. The central region of the star collapses under gravity. It collapses so much that protons and electrons combine to form neutrons. Hence the name ‘neutron star’. If the mass of the pulsar is more than 3 solar masses, it becomes a black hole. The gravitational pull in a black hole is so great that nothing can escape it, not even light. The density of matter in a black hole cannot be measured either. Black holes distort the space around them, and can often suck neighbouring matter into them including stars. |
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A Very Small Star:
If the star is a very small star, then the hydrogen is slowly used up by nuclear fusion. The core of the star also contracts while the outer layers expand, just like a large star. The surface temperature decreases too. This process occurs very slowly, taking billions of years. _
Red Giant:
The next stage for a small star is becoming a red giant. The small star will expand into a red giant. Red giants are stars much smaller than a super-giant. The star will then continue to use up what is left of its hydrogen via nuclear fusion. _
Planetary Nebula:
The next step in a red giants life is a planetary nebula. This is where the red giant blows off its outer atmospheres to form a planetary nebula. This does not include a large violent explosion, similar to a supernova’s. The core materials of the explosion then start too contract. The remnants are less than 1.44 times the size of our Sun. _
White dwarf:
What is left of a planetary nebula becomes a white dwarf. A white dwarf is the remnant of an average-sized star that has passed red giant stage of its life. Once the star has blown off its outer atmosphere (creating a planetary nebula), what remains of it is its dead core of the star. Nuclear fusion can no longer take place. The core glows because of its residual heat. White dwarf stars are very dense. Their size is about the same as Earth’s, but they can contain as much mass as the Sun. They are extremely hot too, reaching temperatures of over 100,000 degrees. Eventually the core will radiate all of its heat into space and cool down to become what is known as a black dwarf. |
Some pictures illustrating the life cycle of a star.
My H-R Diagram