Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 24, Problem 6Q
To determine
The reason for the blueshifted quasars to disprove the hypothesis that quasars might be compact objects ejected at high speeds from the centers of nearby ordinary galaxies.
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Chapter 24 Solutions
Universe: Stars And Galaxies
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- Describe the arguments supporting the idea that quasars are at the distances indicated by their redshifts.arrow_forwardWhy are quasars generally so much more luminous (why do they put out so much more energy) than active galaxies?arrow_forwardWhat is the typical structure we observe in a quasar at radio frequencies?arrow_forward
- In the chapter, we discussed that the largest redshifts found so far are greater than 6. Suppose we find a quasar with a redshift of 6.1. With what fraction of the speed of light is it moving away from us?arrow_forwardDescribe some differences between quasars and normal galaxies.arrow_forwardWhy were quasars and active galaxies not initially recognized as being “special” in some way?arrow_forward
- Suppose you were Hubble and Humason, working on the distances and Doppler shifts of the galaxies. What sorts of things would you have to do to convince yourself (and others) that the relationship you were seeing between the two quantities was a real feature of the behavior of the universe? (For example, would data from two galaxies be enough to demonstrate Hubble’s law? Would data from just the nearest galaxies-in what astronomers call “the Local Group”-suffice?)arrow_forwardIs the appearance of a quasar changing over time a sign that it has entered a new physical state, or are these objects just the extreme outliers of quasars at low activity?arrow_forward3C 273 was the first quasar identified (1963). When we look at its chemical spectrum, we see that its hydrogen alpha emission line (Hα) has an observed wavelength of λobs = 759 nm.-(By comparing the observed wavelength of Hα with the rest-frame (source) wavelength, find 3C 273’s redshift, z.- How fast is 3C 273 moving away from us in km/s?-Assuming the value of Hubble constant listed in the table at the top of the page, how far away is 3C 273 in Mpc? This was, at the time, the most distant object in the known universe!answer to three significant figuresarrow_forward
- Observations of quasars have shown us that many are extremely _________, emitting more energy than all the stars in a galaxy. The energy they give off comes from a very small volume, typically about the size of ___________. Some have long ______, shooting off in opposite directions. Today, astronomers understand that all the properties of quasars can be explained if they are __________ at the centers of galaxies. Astronomers can use _____________ to study images and spectra of the central regions of galaxies more clearly than earlier instruments.arrow_forwardAnother commonly calculated velocity in galactic dynamics is the escape velocity vesc, that is the minimum velocity a star must have in order to escape the gravitational field of the galaxy. (a) Starting from the work required to move a body over a distance dr against f show that the escape velocity from a point mass galaxy is vsc = 2GM/r where r is your initial distance. (b) Since we know galaxies aren't actually point-masses, also show that vesc from r for a galaxy with a p(r) xr¯² density profile is vese that R is a cutoff radius at which the mass density is zero. = 2v(1+ ln(R/r)). Here you must assume (c) The largest velocity measured for any star in the solar neighbourhood, at r=8 kpc, is 440 km/s. Assuming that this star is still bound to the galaxy, find the lower limit (in kiloparsecs), to the cutoff radius R and a lower limit (in solar units) to the mass of the galaxy. Note the solar rotation velocity is 220 km/s.arrow_forward
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