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A star is a hot glowing body of plasma and gases held together by the force of gravity. A star is formed from the gravitational collapse of a nebula, which contains mostly hydrogen and helium. Stars vary in their sizes, temperatures and mass.The energy of a star is the result of the nuclear fusion in its core, which fuses hydrogen to form helium. In fact, other heavier elements in the universe are fused inside stars as well. Which also means that you and I, are technically stardust. While all the stars play a significant role in the universe, the most significant star for human beings on Earth is the Sun, which is the primary source of life in the solar system.
Frequently Asked Questions
How a star is born?
A star is formed when a massive cloud of dust and hydrogen gas collapses itself under its own gravity over a certain period. The center of the cloud is where the core of a star begins to form. AS the center gets denser under gravity, the temperature increases to a point where the hydrogen ions begin to fuse to form helium, releasing enormous energy. The gravity and the pressure from the energy outwards from the core, balances and determines the size of the star then on.
What happens when the star runs out of hydrogen?
When the star runs out of hydrogen, the nuclear fusion stops and the gravity collapses the core and make it even denser. At the same time, the outer layers of the star expand immensely. This stage of a star that is comparable to our sun is known as red giant phase. When the core runs out of helium, the core becomes a denser white dwarf. The outer shell keeps expanding to form a planetary nebula. And gradually over time, the white dwarf turns into a black dwarf.
In the case of a heavier star, when it runs out hydrogen atom and reach the red supergiant phase, the helium in the core fuses to form heavier elements up to iron with the help of gravity. Due to its own heavier mass, the dense core with all the elements collapses very quickly as a violent and massive explosion. This gigantic burst is observed as the supernova. The explosion is staggeringly powerful, enough to outshine its own galaxy for a shorter period. If the core survives the explosion, it either turns into a neutron star or a black hole depending upon the mass of it.
How are the temperature of stars measured?
The star is simply considered as a black body that emits radiation. The temperature of a distant star is measured by analyzing the photons it emits. The light emitted from the star is observed through a spectroscope, where the instrument visualizes the individual wavelengths that the light is composed of. This is called as the black-body radiation spectrum of a star. As this spectrum depends on the temperature of the source, a spectrum curve plotted for corresponding intensity and wavelength will follow the Wien's displacement law. Which means, if the temperature of the star is high, according to the law the black body radiation curve will peak at a shorter wavelength. By comparing it with the known models of such spectrum, the temperature of a star can be defined. This explains why the cooler stars appear red and hotter stars move towards the blue spectrum, appearing yellow and blue.
How is the chemical composition of stars determined?
As explained above, a back body emits radiation in a spectrum of wavelengths. A star is a glowing ball of plasma, which contains different elements, mainly hydrogen and helium. For example, to find out the composition of the Sun, all we need to do is to compare the spectrum of the sun with the individual spectrum of known gases on Earth. As the spectrum of the Sun has several dark lines called as the absorption lines, corresponding to the individual bright spectral lines emitted by specific elements called as the emission lines, it is easy to determine the composition of the Sun.