Question

Suppose a well-known scientist claimed that stars consist primarily of helium rather than hydrogen. a. What type of object in the galaxy could you study to investigate whether stars consist primarily of helium or hydrogen? b. How could spectroscopy help you verify or disprove the scientist's claim? Explain your reasoning.

Short answer

Study stars using spectroscopy to analyze hydrogen and helium lines in their spectra.

Step-by-step solution

Identifying Objects for Study

To investigate whether stars consist primarily of helium or hydrogen, you should study stars directly. Stars are the primary celestial objects where these elements are found in significant quantities. Observing different types of stars, including main sequence stars, giants, and dwarfs, across various stages of their life cycles can provide comprehensive data.

Understanding Spectroscopy

Spectroscopy is a tool that analyzes the light emitted or absorbed by objects. Each element emits or absorbs light at specific wavelengths, producing a characteristic spectrum that acts as a 'fingerprint' for the element.

Analyzing Spectra

By analyzing the spectra of stars, you can determine the levels of hydrogen and helium present. The presence of hydrogen or helium will be indicated by strong absorption lines at specific wavelengths corresponding to these elements' emission lines.

Comparing the Intensity of Lines

Use the intensity and number of absorption lines in the star's spectrum to assess the abundance of hydrogen and helium. If a star primarily consists of helium, its spectrum will feature more prominent helium lines compared to hydrogen lines, and vice versa for a star primarily made up of hydrogen.

Drawing Conclusions from Data

Compare the spectral data from a diverse sample of stars. If most stars show stronger hydrogen lines, this supports the traditional view that stars consist primarily of hydrogen. Conversely, if helium lines are more prominent, this would support the scientist's claim.

Key concepts

Stellar Composition

Stars are extraordinary bodies that comprise various elements, but primarily, they are known to consist of hydrogen and helium. These two elements make up about 98% of most stellar material. The remaining 2% consists of heavier elements, commonly referred to as "metals" in astrophysics, even though this includes elements like carbon, oxygen, and nitrogen. Understanding the composition of stars helps astronomers to glean insights into their formation and evolution.
Studying the composition requires observing stars across different stages of their life cycles: from their birth in star-forming regions to their different end stages like white dwarfs or neutron stars. By examining these bodies in different environments, astronomers can chart how elements within stars change over time, providing clues to their internal processes.
Therefore, the study of stellar composition is not just about cataloging elements, it’s about revealing the history and progression of a star's lifecycle.

Hydrogen and Helium in Stars

Hydrogen is the most abundant element in the universe and it plays a pivotal role in stars by serving as their primary fuel. Through the process known as nuclear fusion, hydrogen nuclei combine under extreme pressure and temperature at a star’s core to form helium, which is the second most abundant element. This fusion releases vast amounts of energy, which, in turn, sustains a star's light and heat.
In the cores of stars like our Sun, hydrogen fusion is the primary reaction occurring. As stars age, the hydrogen is gradually exhausted, and the star begins to fuse helium, leading to different stages in its lifecycle such as turning into a red giant.

• The amount of hydrogen and helium present affects the star's temperature, luminosity, and size.
• Even though helium has a higher atomic number, it is lighter than many other elements formed later.

Understanding the balance of hydrogen and helium within a star is crucial for predicting its future behavior and eventual fate.

Star Spectra Analysis

Spectroscopy provides a powerful method to decode the elemental composition of stars. When light from a star enters a spectrometer, it gets dispersed into a spectrum - much like how a prism splits sunlight into a rainbow. Each element absorbs and emits light at specific wavelengths, and these characteristic patterns appear as lines within the spectrum, unique to each element.
Analyzing the spectra involves identifying the absorption lines associated with hydrogen or helium. For instance:

• Hydrogen lines, known as Balmer lines, appear at well-defined wavelengths in the visible spectrum.
• Helium lines are generally found in the ultraviolet and visible range.

By comparing the relative strengths of these lines, astronomers can determine the proportions of elements within a star. Stronger hydrogen lines in a star's spectrum indicate a higher hydrogen content, whereas stronger helium lines suggest a greater presence of helium.
This data enables scientists to not only infer the primary composition but also to verify or challenge existing theories about stellar formation and evolution. Hence, star spectra analysis is a cornerstone of modern astrophysical research.