Question

Stars exhibit strong hydrogen absorption lines because the surface temperature of 10,000 K is high enough to place most hydrogen in an excited, but not yet ionized, state. The transitions from this excited state then

correspond to visible light wavelengths. Which of the following statements is a plausible explanation for
why G stars exhibit weaker hydrogen absorption lines?

A) G stars are too cool to excite most hydrogen atoms to the first energy level, from which they can then
absorb visible wavelengths of light.

B) At these high temperatures, nearly all the hydrogen is ionized, and unable to interact with light.

C) G stars contain very little hydrogen.

Answer 1

G stars show weaker hydrogen absorption lines because their cooler surface temperatures fail to excite most hydrogen atoms to the necessary energy level for absorbing visible light, resulting in less pronounced Balmer lines compared to hotter stars.

Step-by-step explanation:

G stars exhibit weaker hydrogen absorption lines than hotter stars because of their cooler surface temperatures. Specifically, the temperature of G stars, like our Sun, are too cool to excite most hydrogen atoms to the second energy level, which is necessary for the absorption of visible light to produce strong Balmer lines. Instead, most hydrogen atoms remain in the base or lower energy state, making hydrogen lines in G stars less pronounced compared to stars with temperatures around 10,000 K, where an appreciable number of hydrogen atoms are excited to higher energy levels, thus absorbing more visible light and producing more noticeable lines.

It's not that G stars contain less hydrogen or that the hydrogen is fully ionized; rather, it's the specific energy states that hydrogen atoms occupy at the given cooler temperature of G stars, typically between 5,300 K and 6,000 K, that result in weaker absorption lines. This is because the photons available at these temperatures are not sufficient to excite the hydrogen to the energy level required for more pronounced Balmer absorption lines.