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Young World
WORLD OF SCIENCE
In a haze
DR. T. V. PADMA
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Nebulae are interstellar clouds of dust, gas and particles.
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The word nebula is used to include many non-nebular bodies that appeared hazy upon visual observation, and common usage of this word includes a number of objects. The root of the word is related to the Latin for cloudy or hazy.
In the modern, more restrictive usage, nebulae are interstellar clouds of dust, gas and particles. The particles of gas, dust, and matter in nebulae are too small to see. But if there is a bright star within or close to a nebula, its light illuminates the particles, making the nebula appear like a bright veil of mist. Nebulae that shine by reflected light are called reflection nebulae. Sometimes, the presence of radiation from very hot young stars in a cluster can make the gas glow; such nebulae actually emit their own light and are called emission nebulae.
Protostars
Nebulae are stellar nurseries — places where globules of gas and dust form. These small, dense ‘globules’ of concentrated particles are thought to be protostars — objects that will in time become large enough and hot enough to be stars if their gravity is strong enough to pull more particles inward until the globule grows dense enough to ignite the thermonuclear reactions to become a star.
Some nebulae don’t have stars within or near them to make them glow. These nebulae are called dark nebulae.
Sometimes, at the end of a star’s life, it may undergo expansions and contractions as a result of which some of its hot, glowing gases are thrown off into space forming clouds.
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