This is called Argument from authority and is a logical fallacy.

To steal a good part from wikipedia: Scientific knowledge is best established by evidence and experiment rather than argued through authority[13][14][15] as authority has no place in science.[14][25][26] Carl Sagan wrote of arguments from authority: "One of the great commandments of science is, 'Mistrust arguments from authority.' ... Too many such arguments have proved too painfully wrong. Authorities must prove their contentions like everybody else.