In the graph, each circle represents an individual star. The position of the circle's center indicates the star's temperature in...
GMAT Graphics Interpretation : (GI) Questions
In the graph, each circle represents an individual star. The position of the circle's center indicates the star's temperature in kelvins (K) and its luminosity (rate of energy emission) relative to that of the sun (Lsun). Note that higher temperatures are to the left. The size of the circle indicates the relative physical size of the star, and the labels indicate the types of stars shown.
Select from each of the drop-down menus the option that creates the most accurate statement based on the information provided.
Owning the Dataset
Table 1: Text Analysis
| Text Component | Literal Content | Simple Interpretation |
|---|---|---|
| Circle representation | "each circle represents an individual star" | Each dot in the graph is a different star |
| Position meaning | "position of the circle's center indicates the star's temperature in kelvins (K) and its luminosity" | Where a star is placed shows its temperature (in K) and brightness |
| Luminosity units | "luminosity (rate of energy emission) relative to that of the sun (Lsun)" | Brightness is measured compared to the Sun (Sun = 1) |
| Temperature scale | "Note that higher temperatures are to the left" | Hotter stars are on the left side, cooler on the right |
| Circle size | "size of the circle indicates the relative physical size of the star" | Bigger circles mean physically larger stars |
| Labels | "labels indicate the types of stars shown" | There are different named groups of stars in the data |
Table 2: Chart Analysis
| Chart Component | What's Shown | What This Tells Us |
|---|---|---|
| Chart type | Scatter plot (Hertzsprung-Russell diagram) | Shows how star temperature relates to brightness |
| X-axis | Temperature (K), from about 40,000 (left) to 2,500 (right), reversed | Hottest stars are leftmost, coolest are rightmost |
| Y-axis | Luminosity (Lsun), log scale, from \(10^{-4} \text{ to } 10^6\) | Covers stars much dimmer and much brighter than the Sun |
| Star groups | Five types: main sequence, blue giants, red giants, red supergiants, white dwarfs | Stars cluster in specific areas based on type |
| Main sequence | Diagonal band from upper left (hot, bright) to lower right (cool, dim) | Most stars (including the Sun) follow this pattern |
| White dwarfs | Small, dim, span bottom left with temperature from \(\sim 5,000 \text{ K}\) up to \(\gt 20,000 \text{ K}\) | White dwarfs have the broadest temperature spread outside the main sequence |
Key Insights
The Sun is represented as the main sequence star at luminosity = 1 by definition. White dwarfs (excluding main sequence) span the widest temperature range, from about \(5,000 \text{ K}\) to over \(20,000 \text{ K}\). The main sequence forms a diagonal line, showing a strong correlation: hotter stars are also more luminous, and groups like giants and supergiants stand out as larger and more luminous at lower temperatures.
Step-by-Step Solution
Question 1: Determining the Sun's Stellar Group
Complete Statement:
If it is assumed that one of the stars on the graph represents the sun, it must be that the sun is a [BLANK 1] star.
Breaking Down the Statement
• Statement Breakdown 1:
- Key Phrase: one of the stars on the graph represents the sun
- Meaning: We are to locate the sun among the stars plotted on the chart.
- Relation to Chart: The sun's properties (particularly luminosity) must match a data point and a labeled stellar group on the chart.
- Important Implications: We use the sun's known characteristics to identify its classification among main sequence, red giant, or red supergiant stars.
• Statement Breakdown 2:
- Key Phrase: the sun is a [BLANK 1] star
- Meaning: The sun belongs to only one of the categories listed in the answer choices.
- Relation to Chart: Chart categorizes stars by groups—main sequence, red giant, red supergiant—so the correct answer must be one of these.
- Important Implications: The correct group is where the sun would be plotted based on its luminosity.
• What is needed: Identify which group—main sequence, red giant, or red supergiant—the sun belongs to.
Solution:
- Condensed Solution Implementation:
Find the position where the sun would be located on the graph using its luminosity, which is defined as one solar luminosity (\(L_{\text{sun}} = 1\)). Determine which stellar group this aligns with. - Necessary Data points:
The sun's luminosity = 1 (by definition, in Lsun). On the chart, the main sequence group passes through luminosity 1, while red giant and red supergiant groups are at much higher luminosity values.- Calculations Estimations:
No calculation needed, since the sun's luminosity point is defined in the passage. Visual inspection of the chart shows main sequence at this point. - Comparison to Answer Choices:
Among main sequence, red giant, and red supergiant, only the main sequence group contains stars with luminosity = 1.
- Calculations Estimations:
FINAL ANSWER Blank 1: main sequence
Question 2: Identifying the Non-Main Sequence Group with Greatest Temperature Range
Complete Statement:
Apart from the main sequence stars, the group of stars with the greatest range of temperatures is the group of [BLANK 2].
Breaking Down the Statement
• Statement Breakdown 1:
- Key Phrase: Apart from the main sequence stars
- Meaning: Exclude main sequence stars from consideration.
- Relation to Chart: Focus only on non-main sequence groups, such as red giants, red supergiants, blue giants, and white dwarfs.
• Statement Breakdown 2:
- Key Phrase: group of stars with the greatest range of temperatures
- Meaning: Find the group whose stars' temperatures span the greatest distance along the temperature (horizontal) axis.
- Relation to Chart: Identify the group with the widest spread along the x-axis (temperature), ignoring the main sequence.
• What is needed: Determine which non-main sequence group spans the largest temperature range.
Solution:
- Condensed Solution Implementation:
Visually inspect the chart and compare the ranges along the temperature axis spanned by each non-main sequence group. - Necessary Data points:
White dwarfs range from high temperatures (\(\gt 20,000 \text{ K}\)) to much cooler temperatures (near \(5,000 \text{ K}\)). Other non-main sequence groups (red giants, red supergiants, blue giants) are clustered in narrower temperature ranges.- Calculations Estimations:
Estimate temperature spans: white dwarfs cover about \(5,000 \text{ K}\) to over \(20,000 \text{ K}\) (\(\sim 15,000^+ \text{ K}\) range), much more than any other group. - Comparison to Answer Choices:
White dwarfs clearly have a much greater horizontal spread (temperature range) than red giants, red supergiants, or blue giants.
- Calculations Estimations:
FINAL ANSWER Blank 2: white dwarfs
Summary
The sun must be a main sequence star because its luminosity (by definition 1 Lsun) is only found in that group on the chart. For non-main sequence groups, white dwarfs display the greatest range of temperatures, with their stars extending across most of the temperature axis, much wider than the other groups.
Question Independence Analysis
The two blanks are independent; the first concerns the sun's stellar classification while the second concerns temperature ranges of groups not including the main sequence. The answer to one does not affect the answer to the other.