Why Is 21-Cm Radiation a Good Tracer of Spiral Arm

question 1

Multiple Choice

Why is 21-cm radiation a good tracer of spiral arm structure?

• A) Emitted by neutral hydrogen, it traces the location of high concentrations of gas.
• B) Emitted by O and B stars, it traces the location of newly formed stars.
• C) Emitted by ionized hydrogen, it traces the location of H II regions.
• D) Emitted by molecular hydrogen, it traces the location of clouds in the process of collapsing into stars.
• E) Emitted by red supergiants, it traces the presence of massive stars that are experiencing high rates of mass loss.

---

Definitions:

Protein Catalyst

Enzymes that significantly speed up the rate of virtually all of the chemical reactions that take place within cells.

Chemical Reaction

A process that involves rearrangement of the molecular or ionic structure of substances, not involving a change in physical state.

ATP

Adenosine Triphosphate, a molecule that stores and transfers energy within cells, enabling metabolic processes.

Synthesized

Produced artificially by chemical or biological processes.