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Chapter 16: Problem 15

A white dwarf is located in the lower left of the H-R diagram. From this information alone, you can determine that a. it is very massive. b. it is very dense. c. it is very hot. d. it is very bright.

Short Answer

Expert verified
b. it is very dense.

Step by step solution

01

Understand the Placement on the H-R Diagram

The H-R diagram is a graph that plots stars based on their luminosity and temperature. The lower left corner of the H-R diagram represents stars that have low luminosity and high temperature.
02

Interpret the Characteristics of White Dwarfs

White dwarfs are remnants of stars that have exhausted their nuclear fuel. They are known to be small yet very dense, with a high surface temperature but low overall luminosity.
03

Match Characteristics with the Options

Given the low luminosity and high temperature from the lower left position: - Option a (very massive) is incorrect because white dwarfs are not the most massive stars. - Option b (very dense) is correct because white dwarfs are extremely dense. - Option c (very hot) is partly correct but focuses only on temperature. - Option d (very bright) is incorrect as they are not very luminous.
04

Select the Correct Answer

The correct answer based on the white dwarf’s characteristics and its position on the H-R diagram is: b. it is very dense.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

white dwarf
White dwarfs are fascinating stellar remnants formed when a star has exhausted its nuclear fuel. When they sit on the H-R diagram, they are found in the lower left corner. This specific area signifies that they have a low luminosity and a high temperature. These stars are incredibly dense because they have collapsed from a much larger volume. Despite their small size, a white dwarf can pack a mass similar to that of the Sun into an area comparable to the Earth. This makes them one of the densest forms of matter in the universe, outside of neutron stars and black holes. Typically, a white dwarf has a very thin atmosphere composed mostly of hydrogen or helium.
stellar luminosity
Stellar luminosity refers to the total amount of energy a star emits per unit of time. In simpler terms, it's how bright a star truly is, not just how bright it appears from Earth. The position of a star on the H-R diagram helps in determining its luminosity. In the case of white dwarfs, their position in the lower left corner indicates they have low luminosity. This low luminosity is due to the small surface area of white dwarfs, despite their high temperatures. Understanding luminosity is crucial for astrophysicists as it helps in determining the energy output and life cycle stage of a star.
stellar temperature
Stellar temperature plays a critical role in determining a star’s color and position on the H-R diagram. The term 'stellar temperature' usually refers to the surface temperature of a star. For white dwarfs, this temperature can be quite high, often reaching up to 100,000 Kelvin. This high temperature is what places white dwarfs in the lower left corner of the H-R diagram. The blue or white color seen in white dwarfs is indicative of their high temperatures. Unlike larger stars, the temperature of white dwarfs does not significantly affect their level of luminosity.
stellar density
Stellar density is a measure of how much mass a star has relative to its volume. White dwarfs are exceptional when it comes to density. They boast incredibly high density because they are formed from stars that have expended all their nuclear fuel, causing them to collapse into a very compact object. The density of a white dwarf is so immense that a teaspoon of its material would weigh several tons on Earth. This extreme density results from the gravitational forces compressing the star's matter into a much smaller volume, creating a significant and fascinating point of study for astrophysicists.

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