A nebula basically is a non-basic thing which more complicates the unexplored universe and is based upon the development of planets.A nebula is a cluster of collapsed gases like helium,hydrogen and other gases present in space.When all of these react with each other they form a nebula which means a cloud which shines because of reaction of gases.This is true that space is a vacuum but not completely as you know light travels through vacuum so it needs friction which is only possible through gases so whole outer space is full of gases.
The nebula's soon when condensed becomes solid and turns into planet and if the condition of planet is favourable for life than organisms take birth on those planets.Our earth itself is a condensed nebula and there are many around the space.There are unlimited nebula's in the universe around each with its own density and mass but the most highly densed found till now is so highly densed that only one spoon full of this nebula is of 300 million tones which is more than 10 times of eiffel tower.
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