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: Some [[Solar System]]s have more than one [[Star]].
: The [[planet]]s around a [[star]] which is not the [[Sun]] are called [[exoplanet]]s.
===Formation of Solar Systems===
#A large cloud of [[gas]]] and dust called a [[nebula]] collapses due to [[gravity]] to form a [[protostar]].
#Some of the leftover [[gas]] and dust forms a spinning disk held in [[orbit]] around the newly formed [[star]] by [[gravity]].
#The [[star]]s [[radiation]] caused the [[gas]] to spread further away from the centre of the disk leaving behind the dust.
#[[Gravity]] between the [[particle]]s of dust causes them to clump together to form [[asteroid]]s.
#Over millions of [[year]]s [[gravity]] causes the [[asteroid]]s collide to form bigger and bigger [[asteroid]]s until they are so large that they have enough [[gravity]] to pull their [[matter]] in to a [[sphere|spherical]] shape and become [[Dwarf Planet|dwarf planets]].
#Eventually the [[Dwarf Planet|dwarf planets]] may sweep enough [[material]] out of their [[orbit]]al path that they are considered [[planet]]s.