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How many galaxies are there? what is Nebula?
The best estimate from a 1999 study set that number at about 125 billion galaxies, but a 2013 study indicated that there are 225 billion galaxies in the observable universe.
A nebula is an interstellar cloud in outer space that is made up of dust, hydrogen and helium gas, and plasma. It is formed when portions of the interstellar medium collapse and clump together due to the gravitational attraction of the particles that comprise them. 



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