 channel for physics. Please subscribe my channel. Hello and welcome back to another episode of Physics Partner. Today's video is the fourth part of the space series newly injected in IGCC physics curriculum for the core 0625 and 0972. In today's video we will study about stars and the life cycle of stars. In spite of this fact that sun is extremely bigger as compared to earth, it might surprise for you that our sun is still a very medium-sized star with a radius of about 700,000 kilometers. Many stars are much, much larger. The sun is a huge ball of hydrogen and helium held together by its own gravity. The sun sends most of its energy to earth in a few different ways. Visible light that you can see, infrared radiation that you feel as heat and rays of UV radiation that you can't see or feel. Fortunately, the earth's atmosphere protects us from most UV radiation. In the core of sun, hydrogen is being converted into helium. This process is called nuclear fusion. It takes four hydrogen atoms to fuse into each helium atom. During this process, some of mass is converted into energy. This energy is the life on the earth. The sun is like a big nuclear submarine in the sky. It's fueled by nuclear reaction that fuse hydrogen atoms together into helium and other heavier elements, releasing huge amount of energy in the process. But this is not the total universe. The galaxies are each made up of many billions of stars, huge than our sun. The sun is a star in our galaxy known as the Milky Way, but other stars that make up the Milky Way are much further away from the earth than the sun. Let's see how we measure these distances. The distance between stellar objects is called astronomical distance in terms of astrophysics. It can be measured in light years, which one light year is the distance traveled in approximately vacuum. It's about 9.5 times the power of 15 meters. Let's move to the second part of the video, the life cycle of a star. Like human beings, stars have also life cycle. Stars come into a variety of masses and the mass determines how radiantly the star will shine and how it dies. Massive stars transform into supernova, neutron stars and black holes, where every star like the sun and life as a white dwarf surrounded by a disappearing planetary nebula. All stars, irrespective of their sizes, follow the same stage cycle. They start their life as a gas cloud and end as a star remnant. All stars start their life from gas and dust and turn into nebula, which is actually a huge cloud of gas and dust. Through this shine for many thousands and even millions of years, stars do not last forever. They change the occur in star over time and the final stage of its life depends on the star's size. A protostar is an interstellar cloud collapsing and increasing in temperature as the results of its internal gravitational attraction. Nuclear reaction at the center of the core of a star provides energy, which makes it shine brightly. This stage is called the main sequence. The exact lifetime of a star depends very much on its size. Very massive stars use up their fuel quickly because they require more fuel to survive. This means they may only last for a few hundred thousand years. Smaller stars use up fuel more slowly so will shine for several billion years. Eventually, the hydrogen which powers the nuclear reaction inside a star begins to run out. The star that enters the final phase of its lifetime, all stars will expand, cool, and change color to become a red giant. What happens next depends on how massive the star is. A smaller star like a sun will gradually cool down and stop glowing. During these changes, it will go through the planetary nebula phase and white dwarf phase. After many thousands of millions of years, it will stop glowing and become a black dwarf. A massive star, more than the sun, experiences a much more energetic and violent end. It explodes as a supernova, which is the beautiful stellar object. It may form new stars with orbiting planets. After the dust clears, a large, very dense neutron star is left behind. If the star is especially massive, when it explodes, it forms a black hole. This is how we can describe the life cycle of the star. So I think it's enough for today. So thank you very much for listening and watching. I hope you enjoyed the video. I hope this video is useful for you. So take care of yourself and don't hesitate to write an email if you have any questions, queries, suggestions, and even classes are required. Take care of yourself. Meanwhile, see you in the next video. Goodbye.