Question

question 9 of 19
which of the methods is used to detect neutral hydrogen (hi) in the interstellar medium?
○ tachyon particles
○ hα lines
○ 21 cm radiation
○ gamma rays
○ tracer particles, such as co
high velocity clouds
the orange and yellow patches in this image of the galaxy are clouds of neutral hydrogen.
image composite credits: ingrid kallick of possible designs, madison wisconsin.
background milky way image: lund observatory. high - velocity clouds: dwingeloo observatory (hulsbosch & wakker, 1988).

Explanation:

Neutral hydrogen (HI) in the inter - stellar medium is detected through 21 cm radiation. This is because the electron in a neutral hydrogen atom can change its spin relative to the proton, and this transition emits a photon with a wavelength of 21 cm. Tachyon particles are hypothetical faster - than - light particles and not related to HI detection. Hα lines are related to ionized hydrogen. Gamma rays are high - energy electromagnetic radiation and not used for HI detection. Tracer particles like CO are used to trace molecular gas, not neutral hydrogen.

Answer:

21 cm radiation