Life Cycle & Classification Of Stars

Explanation
Energy is released in stars through the process of nuclear fusion. This is the process where the nuclei of atoms combine to form a heavier nucleus, releasing a large amount of energy in the process. In stars, hydrogen nuclei combine to form helium, releasing a tremendous amount of energy in the form of light and heat. Nuclear fission, on the other hand, is the process of splitting heavy atomic nuclei into smaller ones, and gravitational attraction is the force that pulls objects towards each other due to their mass. However, in the context of energy release in stars, nuclear fusion is the correct answer.

Explanation
Stars are primarily composed of hydrogen gas. This is because hydrogen is the most abundant element in the universe and provides the fuel for nuclear fusion reactions that occur within stars. These fusion reactions release immense amounts of energy, which is what allows stars to shine brightly. While other elements, such as helium and carbon, can also be present in stars, hydrogen is the main element that fuels their existence.

Explanation
In about 4 billion years, our sun will exhaust its hydrogen fuel and start burning helium, causing it to expand and become a red giant. During this phase, the sun will increase in size and become much brighter, potentially engulfing the inner planets, including Earth. This transformation is a natural stage in the life cycle of a star like our sun. A red dwarf is a smaller and cooler star, while a red supergiant is a much larger and more massive star, so they are not the correct answer in this case.

Explanation
Massive stars, which have a much larger mass than the Sun, undergo a violent explosion at the end of their life known as a supernova. During a supernova, the star releases an enormous amount of energy and matter into space, creating a bright and powerful explosion that can outshine an entire galaxy. This explosion also disperses heavy elements and enriches the surrounding space with these elements, providing the building blocks for future star formation. Therefore, the correct answer is supernova.

Explanation
Stars begin as nebulae, which are large clouds of gas and dust in space. These nebulae are composed mostly of hydrogen and helium, along with small amounts of other elements. Over time, the gravitational forces within the nebula cause it to collapse inward, leading to the formation of a protostar. As the protostar continues to contract, its core becomes dense and hot enough to initiate nuclear fusion, resulting in the birth of a star. Therefore, the correct answer is "Nebula."

Explanation
Blue stars burn the hottest because they have the highest surface temperature. The color of a star is determined by its surface temperature, with hotter stars appearing blue and cooler stars appearing red. Blue stars have temperatures of over 10,000 Kelvin, while red stars have temperatures below 3,500 Kelvin. The higher temperature of blue stars means that they emit more energy and burn hotter than stars of other colors.

Explanation
When a star consumes fuel, it undergoes a process called nuclear fusion in its core. During this process, hydrogen atoms combine to form helium atoms, releasing a tremendous amount of energy. Therefore, helium is the by-product created when a star consumes fuel.

Explanation
Smaller stars have longer lifespans compared to larger stars. This is because smaller stars, such as red dwarfs, burn their fuel at a slower rate than larger stars. The main factor determining a star's lifespan is its mass. Smaller stars have less mass and therefore less gravitational pressure, resulting in slower fusion reactions and a longer lifespan. In contrast, larger stars burn through their fuel more quickly due to higher temperatures and pressures, leading to a shorter lifespan.

Explanation
Stars can be classified based on their mass and color. Mass classification categorizes stars into different groups based on their size and weight, ranging from dwarf stars to supergiant stars. Color classification, on the other hand, classifies stars based on their temperature, with cooler stars appearing red and hotter stars appearing blue. Therefore, both mass and color are used as ways to classify stars.

Explanation
A green giant is not a known type of star. Stars come in various colors, including blue super giants and brown dwarfs, but green giants do not exist. The color of a star is determined by its temperature, and green is not within the range of possible colors for stars. Blue super giants are massive and extremely hot stars, while brown dwarfs are failed stars that are not massive enough to sustain nuclear fusion.