Stellar Evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the age of the universe. All stars are born from collapsing clouds of gas and dust, often called nebulae or molecular clouds. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main sequence star. A protostar is a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation.
When you look at the night sky you can see many beautiful stars. There are several different kinds of stars in the sky. Some are very big. A couple of stars have been found that are 100 to 200 times larger than the sun. Some very old stars are smaller than the Earth. Scientists study stars and place them in groups based on how they are alike and how they are different. And see many beautiful stars
Ever wondered where stars are made? Well, now you are about to find out! Just where these hot balls of gas start their lives begins in what astronomers call a nebula (plural: nebulae) and they are basically the nurseries of the Universe. Do you want to know more about the formation of stars?
Different Kinds of Stars
Stars are mainly huge balls of gas held together by gravity that give off light and heat. But there are also many different kinds of stars. Stars have different colours, sizes, and temperatures.
Brightness of Stars
Stars are all made of the same materials. But stars come in many different sizes and have different brightness’s. When we observe them at night from Earth, they all look as if they are all the same distance away from us, but truly, all the stars are from different distances away. If we just look at the star from Earth, we can't tell how bright a star is. Astronomers invented two different systems to tell how bright a star is. The apparent magnitude scale tells how bright a star is as it appears on Earth, and the absolute magnitude scale tells how bright the star really is. Magnitude is the term astronomers use to measure the brightness of a star.
Star Colours
Star Colours
Of course, when you first look at a star, it seems that they are all the same colour. But while observing the stars carefully, you can see a little colour, such as blue and orange .Stars is grouped together by what astronomers call spectral classification. This groups the star by its colour, composition, and size. For example, an O type star has a colour of blue and its temperature is 70,000 degrees Fahrenheit. B type star is blue-white and is about 33,700 degrees Fahrenheit. An A type star is white and is about 15,000 degrees Fahrenheit. F type star is also white but it is about 12,000 degrees Fahrenheit. G star is yellow and is about 9,400 degrees Fahrenheit (the sun is a G star). K type star is orange and is about 7,200 degrees Fahrenheit. Finally, M type star is red and is 4,900 degrees Fahrenheit. As you see, the duller the color of the star is, the cooler it is.
The Hertzsprung-Russell diagram is a scatter graph of stars showing the relationship between the star’s absolute magnitudes or luminosities versus their spectral types or classifications and effective temperatures. Hertzsprung-Russell diagrams are not pictures or maps of the locations of the stars. Rather, they plot each star on a graph measuring the star’s absolute magnitude or brightness against its temperature and colour.
Light year
Birth of Stars
A nebula is a cloud of gas and dust in space. Astronomers think a star's explosion causes this cloud to spin. While it is spinning and moving, gravity from the gases, rocks, and dust pull itself together in the cloud. These things in the centre of the nebula become very tightly packed. This causes the atoms of gas to fuse together. When this happens, enormous amounts of energy are released. The gases in the nebula then shine because of the energy that was released. If the star turns out big or small all depends on the amount of material in the cloud.
Light year is the unit commonly used for stating large distances such as the distance of stars. One light year= 9.46×1012 kilometres i.e. the distance travelled by light in one year. The distance from the sun to the nearest star is 41/4 light years. The distance from one edge of our galaxy to the other edge is about one lakh light years. The distance of the adjacent galaxy Andromeda from our galaxy is estimated to be 24 lakh light years.
A nebula is a cloud of gas and dust in space. Astronomers think a star's explosion causes this cloud to spin. While it is spinning and moving, gravity from the gases, rocks, and dust pull itself together in the cloud. These things in the centre of the nebula become very tightly packed. This causes the atoms of gas to fuse together. When this happens, enormous amounts of energy are released. The gases in the nebula then shine because of the energy that was released. If the star turns out big or small all depends on the amount of material in the cloud.
Binary Stars
Sometimes the cloud might have enough material to create two stars or even more. Most nebulae seem to create more than one star most of the time. When a nebula creates two stars that orbit each other, they are called binary stars. When a nebula forms more than two stars that orbit around each other, they are called multiple stars.
Sometimes the cloud might have enough material to create two stars or even more. Most nebulae seem to create more than one star most of the time. When a nebula creates two stars that orbit each other, they are called binary stars. When a nebula forms more than two stars that orbit around each other, they are called multiple stars.
Binary star formation
Star Clusters
Clusters of stars can form from one nebula and then they live bounded together by gravity. They are called globular (a cluster of stars that form a globe shape), or open or galactic star clusters (star clusters that don't have any specific shape).
Clusters of stars can form from one nebula and then they live bounded together by gravity. They are called globular (a cluster of stars that form a globe shape), or open or galactic star clusters (star clusters that don't have any specific shape).
Death of a Star
Stars like the sun will cool at the centre and shrink a little before an inward fall of material causes an explosion to take place. The small explosion will turn the star into a large, red star, or in other words, a red giant.. When the centre of the star contracts enough, the shrinking will stop. The star will brighten up again. A planetary nebula will burst from the surface and is then thrown outward. A planetary nebula is a sphere of gases. After that, the only thing remaining is a small star that will lose energy and become a white dwarf star. White dwarf stars are the size of a planet.. Stars smaller than the sun will not create a planetary nebula, they will just shrink to a white dwarf star.
Supernovas
Black Holes
If a star has more than ten times the mass of the Sun, the remaining core from the supernova will shrink even smaller than a neutron core. The more mass the star has, the greater its gravity. The greater the gravity, the more force there is to pull the stars outer layer inward. The star will collapse so tightly that its gravity gets greater and greater. The gravity will become so strong that nothing can escape from it, even light can't escape from it. This is called a black hole. Scientists don't actually know if black holes do exist but a lot of evidence supports the theory
Pulsars
The gases in the centre of the neutron core left over from the supernova explosion spin thirty times per second. As it spins, the radiation beams out. The fast rotating star is a pulsar. We can learn about pulsars by studying light, heat, radio waves, and x-rays.
The gases in the centre of the neutron core left over from the supernova explosion spin thirty times per second. As it spins, the radiation beams out. The fast rotating star is a pulsar. We can learn about pulsars by studying light, heat, radio waves, and x-rays.
Energy generation in stars
Energy is generated in the sun and the stars by the process of fusion taking place at their core. At very high temperature, four hydrogen nuclei combine to form a helium nucleus, nuclear fusion takes place. The mass of the helium nucleus thus formed is slightly less than the mass of the four hydrogen nuclei (7 in 1000 parts).This mass is converted into energy the application of Einstein’s equation E=mc2 (E energy ,m=mass=velocity of light ) is what takes place here. In the sun 40 lakh tons of hydrogen is converted into helium every second.
How does matter attain the high temperature required for this? The gaseous clouds in the interstellar space are the birth place of stars. There are known as nebula. They contain the gases hydrogen and helium and small quantity of certain other element .The contraction of the gaseous cloud in the nebula due to gravitation, initiates the birth of a star. Gases and dust move continuously and come closer, and contract to the centre of the nebula due to increased gravitation. This cramming due to gravitation provides the temperature required to initiate function. A star becomes visible to us only when the energy due to fusion is produced
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