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Chapter 15: Problem 34

Molecular hydrogen is very difficult to detect from the ground, but astronomers can easily detect carbon monoxide (CO) by observing its 2.6 -cm microwave emission. Describe how observations of CO might help astronomers infer the amounts and distribution of molecular hydrogen within giant molecular clouds.

Short Answer

Expert verified
Observing CO emission helps infer molecular hydrogen quantities and distribution in giant molecular clouds because CO serves as a reliable tracer for H2.

Step by step solution

01

- Understanding Detection Difficulties

Molecular hydrogen (H2) is very difficult to detect via ground-based observations because it doesn't emit in the visible or easily accessible parts of the electromagnetic spectrum.
02

- CO as a Molecular Tracer

Carbon monoxide (CO), however, emits strong microwave radiation at a wavelength of 2.6 cm, which can be easily detected by radio telescopes, making it a reliable tracer of molecular gas.
03

- Ratio of CO to H2

Astronomers use the known ratio of CO to H2, often determined from theoretical models and empirical data in various environments, to estimate the amount of molecular hydrogen. This ratio is usually constant.
04

- Mapping CO Emissions

By mapping the distribution and intensity of CO emissions in giant molecular clouds, astronomers can visualize where molecular hydrogen is likely to be present.
05

- Inferring H2 Distribution

The CO emission maps provide indirect evidence of the H2 distribution within these clouds, allowing astronomers to infer both the locations and amounts of molecular hydrogen.

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Key Concepts

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

Carbon Monoxide Emission
Carbon monoxide (CO) is a key molecule for astronomers because it emits strong microwave radiation at a wavelength of 2.6 cm.
This specific wavelength falls within the range that can be easily detected by radio telescopes.

Unlike molecular hydrogen (H2), which doesn't emit in detectable parts of the spectrum, CO is readily visible in microwave frequencies.
This makes CO a valuable tracer for studying molecular gas in space.
Understanding CO emission helps astronomers overcome the challenges of directly observing H2.
Radio Telescopes
Radio telescopes play a crucial role in the detection of carbon monoxide emissions.
They are designed to observe radio waves from celestial sources, including the 2.6 cm wavelength emitted by CO.

These telescopes are equipped with large dishes that capture and amplify weak signals from space.
By scanning the sky, radio telescopes can map the distribution of CO emissions across vast regions like giant molecular clouds.
This technology allows astronomers to gather high-resolution data and infer the presence of molecular hydrogen indirectly.
Molecular Gas Tracing
Molecular gas tracing involves using certain molecules, like CO, to detect the presence of other molecules that are harder to observe directly.
Since H2 doesn't emit strongly in accessible wavelengths, CO is used as a proxy.

By studying CO emissions, astronomers can estimate the amount and distribution of H2 within a giant molecular cloud.
They do this by applying known ratios of CO to H2, which have been derived from both theoretical models and empirical observations in different environments.
This method provides a practical solution to the challenge of H2 detection.
Giant Molecular Clouds
Giant molecular clouds (GMCs) are vast regions in space containing large amounts of molecular gas, primarily H2.
These clouds are the birthplaces of new stars and can span hundreds of light-years.

Observing and understanding these clouds is vital for studying star formation and the dynamics of our galaxy.
However, because H2 is difficult to detect directly, astronomers rely on CO emissions to map these clouds.
The data from CO observations help delineate the structure and composition of GMCs, providing insights into their physical properties and behavior.
H2 Distribution Mapping
Mapping the distribution of H2 involves analyzing CO emissions to create detailed maps of molecular hydrogen.
These maps show where H2 is likely to be concentrated within giant molecular clouds.

By examining the intensity and spread of CO emissions, astronomers can infer the relative abundance and locations of H2.
These H2 distribution maps are crucial for studying the processes of star formation and the evolution of molecular clouds.
They also help astronomers understand the gas dynamics in our galaxy and the universe.

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Most popular questions from this chapter

The Milky Way contains several thousand giant molecular clouds. Describe a giant molecular cloud and the role it plays in star formation.

Astronomers know that there are dusty accretion disks around protostars because a. there is often a dark band across the protostar. b. there is often a bright band across the protostar. c. theory says accretion disks should be there. d. there are planets in the Solar System.

Molecular clouds fragment as they collapse because a. the rotation of the cloud throws some mass to the outer regions. b. the density increases fastest in the center of the cloud. c. density variations from place to place grow larger as the cloud collapses. d. the interstellar wind is stronger in some places than others.

What is the single most important property of a star that will determine its evolution? a. temperature b. composition c. mass d. radius

If a typical hydrogen atom in a collapsing molecular-cloud core starts at a distance of \(1.5 \times 10^{12} \mathrm{km}(10,000 \mathrm{AU})\) from the core's center and falls inward at an average velocity of \(1.5 \mathrm{km} / \mathrm{s},\) how many years does it take to reach the newly forming protostar? Assume that a year is \(3 \times 10^{7}\) seconds.
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