What was the first evidence that quasars were different from astronomical objects before they were observed in visual wavelengths?

Question

Quizplus · Accepted Answer

The emission of radio energy like active galaxies, but appearing as point sources in radio wavelengths, was the first evidence that quasars were different from other astronomical objects. Quasars emitted radio energy like active galaxies, but appeared to be point sources in radio wavelengths, indicating that they were very small and located very far away. This was the first evidence that quasars were different from known astronomical objects before they were observed in visual wavelengths.

What Was the First Evidence That Quasars Were Different from Astronomical