Question

what is nebula ? how it is formed

Answer 1

nebulae, nebulæ, or nebulas) is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, nebula was a name for any diffuse astronomical object, including galaxies beyond the Milky Way. ...Nebulae are often star-forming regions, such as in the "Pillars of Creation" in the Eagle Nebula.

Answer 2

Nebula is a part of universe which is present at different places in the universe. Only very less Nebulas are found. This nebula is very harmful for human being. It radiates alpha and gama particles. When it is seen from far distance it look coloured.

It is formed of different harmful gases.