The claim that stellar surfaces are physically unreachable by human hands due to extreme temperatures is a matter of everyday scientific fact and basic observation; no formal citation is needed.
The claim is trivially true by definition and basic thermodynamics, as stellar surfaces possess extreme temperatures (thousands of degrees Celsius) that would instantly destroy human tissue and spacecraft alike. Per instructions, trivial or everyday physical facts are categorized as COMMON_KNOWLEDGE and do not require supporting citations from the literature.