which part of the electromagnetic spectrum helped astronomers understand that the crab nebula contains…

which part of the electromagnetic spectrum helped astronomers understand that the crab nebula contains hydrogen?\n○ gamma rays\n○ microwaves\n○ radio waves\n○ visible light
Answer
Brief Explanations:
Astronomers use radio - waves to detect hydrogen in the Crab Nebula. Hydrogen emits a spectral line at a specific radio - wave frequency known as the 21 - centimeter line. This allows astronomers to map the distribution of hydrogen in space.
Answer:
C. radio waves