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Chapter 4: Problem 7

A spectrum of a distant object reveals a sequence of known absorption lines that are all shifted to shorter wavelengths. What can be concluded about the object? a. It must be very massive. b. It must be highly magnetized. c. It must be emitting cosmic rays. d. It must be moving away from us. e. It must be moving toward us

Short Answer

Expert verified
The object is moving toward us (Option e).

Step by step solution

01

Understanding the Shift in Wavelengths

In astronomy, when absorption lines in a spectrum are observed to shift, it can indicate the movement of the object relative to us. If lines shift towards shorter wavelengths (blue end of the spectrum), this is known as 'blueshift.' A shift towards longer wavelengths (red end) is called 'redshift.' Determine which phenomenon applies here.
02

Interpreting the Blueshift

The exercise specifies that absorption lines are shifted to shorter wavelengths, indicating a blueshift. A blueshift implies that the object is moving towards us, as the light waves are compressed, making them appear shorter.
03

Analyzing the Options

Consider each option: (a) Mass does not directly cause blueshift; (b) Magnetization affects light in different ways, not necessarily causing blueshift; (c) Cosmic rays emitting does not cause a blueshift; (d) Redshift, not blueshift, occurs when moving away; (e) Movement towards us causes blueshift. Option (e) fits the evidence.

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Key Concepts

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

Blueshift
Blueshift is an important concept in astrophysics. It's observed when the wavelengths of light from an object in space shift towards the blue end of the electromagnetic spectrum. This occurs due to the Doppler Effect, which happens when an object moves towards an observer. The light waves are compressed, leading to shorter wavelengths. This makes the light appear bluer than it otherwise would.

In more understandable terms, think of it like a fast-approaching vehicle. The sound appears higher in pitch as it comes closer. Similarly, the light from stars or galaxies gets shifted towards blue as they approach Earth.
  • Blueshift indicates approaching motion relative to the observer.
  • It's crucial for understanding cosmic movements.
  • It helps astronomers determine the speed and direction of celestial objects.
Redshift
Redshift is the counterpart of blueshift in the study of celestial motions. When light from an object shifts towards the red end of the spectrum, it indicates that the object is moving away from the observer. This too is a result of the Doppler Effect. The key idea is that as an object moves further away, the light waves stretch, making them appear longer.

To visualize this, think about a siren on a passing ambulance. As it moves away, the pitch of the sound seems to lower. Just like that, the light elongates in wavelength toward red when a star or galaxy recedes.
  • Redshift shows that an object is moving away from the observer.
  • It's vital for measuring the expanding universe.
  • Hubble's Law utilizes redshift to estimate distances in the universe.
Spectroscopy
Spectroscopy is a technique used to study the light spectrum emitted or absorbed by substances. It is highly significant in astronomy for determining the composition, temperature, density, and motion of celestial objects. When light passes through a medium or reflects off surfaces, it can split into its spectrum of colors, much like raindrops creating a rainbow.

Different chemical elements absorb light at specific wavelengths, leaving distinct patterns or lines in the spectrum. The study of these lines lets astronomers deduce an object's constituents and conditions.
  • Spectroscopy reveals the "fingerprints" of elements present in stars.
  • It helps understand physical properties like temperature and pressure.
  • The movement of spectral lines can indicate shifts鈥攔edshift or blueshift鈥攕howing motion relative to Earth.
Absorption Lines
Absorption lines are dark lines or gaps that appear in the light spectrum when light passes through a gas or atmosphere. This occurs because certain wavelengths of light get absorbed by atoms or molecules present in the medium. Each element absorbs light uniquely, which helps create a pattern of lines specific to that element.

Think of absorption lines as an object's DNA in the spectrum. By studying these lines, scientists can identify what materials a star or planet is made of and offer insight into its environment and motion.
  • Absorption lines are crucial in identifying chemical compositions.
  • They allow for the identification of physical states of matter.
  • Shifts in absorption lines help detect the movement of celestial bodies鈥攚hether they are moving away or towards Earth.

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Most popular questions from this chapter

In observing an oxygen emission line from a warm gas cloud that is expected to appear at \(500 \mathrm{nm}\), the line is seen at \(525 \mathrm{nm}\) instead \((5 \%\) longer). Which of the following is true? a. The object is moving away from the observer at \(5 \%\) of the speed of light. b. The object is moving toward the observer at \(5 \%\) of the speed of light. c. The observed emission line indicates that a chemical change has occurred. d. The velocity of the light is greater than expected. e. The observer's equipment is inaccurate, since emission lines do not change.

Arrange the following regions of the electromagnetic spectrum from lowest to highest frequency: infrared, gamma-ray, optical, X-ray, ultraviolet, radio. a. X-ray, gamma-ray, ultraviolet, infrared, radio, optical b. gamma-ray, X-ray, ultraviolet, optical, infrared, radio c. gamma-ray, infrared, optical, radio, ultraviolet, X-ray d. radio, infrared, optical, ultraviolet, X-ray, gamma-ray e. optical, radio, infrared, ultraviolet, gamma-ray, X-ray

Why do stars twinkle? a. The stellar surface where the light is emitted is very turbulent. b. Stars are constantly changing their brightness. c. The distribution of absorption lines in their atmospheres is changing. d. The motion of Earth's atmosphere creates the appearance of twinkling. c. Our cyes are constantly moving.

You have a reflecting telescope with a 6 -inch aperture. Your sister has one with a 10 -inch aperture. What is the ratio of the light-gathering power of her telescope to that of yours?

How might life on Earth differ if all wavelengths of light could pass through the atmosphere?
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