Star

False Image of The Sun[Image Credit NASA]

    A Star is a ball of plasma and is a very dense region in space. In the night sky, you can see an uncountable number of stars and even though they look so little, most of them are several times larger than our parent star, The Sun, which is only an average-sized star. A star is capable of helping sustain life on a planet if it is placed at the right distance from its parent star.

    One might ask, how does a star shine or how does it generate heat. The answer is Nuclear fusion. Abundant quantities of hydrogen are present in any star. Due to high densities, the hydrogen atoms undergo fusion producing helium and in the process liberate very high amounts of heat and also photons(i.e, light). Every second, around 600 million tons of hydrogen are converted into 596 million tons of helium and the remaining 4 million tons are converted into energy.

Carina Nebula[Image Credit: NASA, ESA, Hubble Space Telescope] 

   A star is born from a nebula which is a cloud of hydrogen, helium, and dust. Over time this cloud comes closer and closer because of gravitational force and after a certain density is reached, nuclear fusion starts, and the star starts emitting light and energy. A typical star continues to burn for many billion years before it runs out of fuel, hydrogen. As it loses more and more hydrogen, the density decreases because of which the gravitational force decreases, and the size increases becoming a red giant. When the Sun becomes a red giant, it is estimated that it will cover the till the orbit the earth, consuming mercury, venus, and earth in the process. Other planets would be also affected by this conversion like change in their orbits, change in their atmosphere, etc. After it runs out of the fuel, due to still high the star then collapses into itself due to gravity. When it collapses, it triggers nova, which is a large explosion of most of its matter. Stars twice as big as the sun explodes with very high magnitude and the explosion is called supernovae. Based on the size of the star, after the explosion, it collapses to form different objects. Where a star with the size of the sun collapses it forms a white dwarf, which is much much smaller than the original size. If a star twice as big or much larger than that collapses, it becomes a neutron star. Gravity is so strong that the atoms tears apart and proton and electrons combine to form neutrons, so the existing and newly made neutrons are tightly packed with each other in a neutron star. Stars which are 20 times as big as the sun can collapse into a black hole. Gravity in a black hole is immensely strong that all the matter collapses into a single 1-dimensional point and nothing, not even the light can escape from it.

    There are many ways a star can exist in the universe. There can be a lone star that wanders the universe without any destiny. Another can exist in a galaxy where it orbits the supermassive black hole at the center of the galaxy. There can be planets orbiting the star just like our solar system. Two or more stars can orbit each other while planets may be orbiting them or may not. Even though more than 2 stars orbiting each other is pretty much abnormal. When two stars orbit each other its called a binary system.

    In contrast to popular beliefs, red stars are cooler than blue stars. Also, the bigger the star is, the faster it burns the fuel, and the earlier the star dies. This is why very large stars are rare in the universe as they died in the earlier years of the universe. The biggest star known to us today is, UY Scuti which is about 1700 times the size of the Sun.

Sun compared to UY Scuti[Image Credit: