Horizons: Exploring the Universe (MindTap Course List)
14th Edition
ISBN: 9781305960961
Author: Michael A. Seeds, Dana Backman
Publisher: Cengage Learning
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Chapter 12, Problem 1DQ
To determine
The difference in our understanding of Milky Way galaxy if interstellar dust was not present
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The very first “image" of a black hole, at the centre of galaxy M87, was recently taken by the
Event Horizon Telescope (EHT). More accurately, EHT imaged radio emission from the disc
of gas that orbits the black hole with a lack of emission from the centre being attributed to
the black hole. This image was only possible because EHT is not a single radio telescope, but
is in fact a network of telescopes from around the world that take advantage of something
known as interferometry. Interferometry is a method for combining the light from multiple
telescopes, which results in an image that could have been taken by a telescope that has a
diameter equal to the distance between the telescopes referred to as the "“baseline"-rather
than the size of each individual telescope. EHT in particular combines observations from
several Very Long Baseline Interferometry (VLBI) stations in order to achieve a high angular
resolution.
(a) Given that the "baseline" of EHT is effectively the diameter of the…
The very first "image" of a black hole, at the centre of galaxy M87, was recently taken by the
Event Horizon Telescope (EHT). More accurately, EHT imaged radio emission from the disc
of gas that orbits the black hole with a lack of emission from the centre being attributed to
the black hole. This image was only possible because EHT is not a single radio telescope, but
is in fact a network of telescopes from around the world that take advantage of something
known as interferometry. Interferometry is a method for combining the light from multiple
telescopes, which results in an image that could have been taken by a telescope that has a
diameter equal to the distance between the telescopes-referred to as the “baseline"-rather
than the size of each individual telescope. EHT in particular combines observations from
several Very Long Baseline Interferometry (VLBI) stations in order to achieve a high angular
resolution.
(a) Given that the "baseline" of EHT is effectively the diameter of the…
Chapter 12 Solutions
Horizons: Exploring the Universe (MindTap Course List)
Ch. 12 - Why is it difficult to specify the dimensions of...Ch. 12 - Why didn’t astronomers before Shapley realize how...Ch. 12 - Prob. 3RQCh. 12 - Prob. 4RQCh. 12 - Prob. 5RQCh. 12 - Prob. 6RQCh. 12 - Prob. 7RQCh. 12 - Prob. 8RQCh. 12 - Prob. 9RQCh. 12 - Prob. 10RQ
Ch. 12 - Prob. 11RQCh. 12 - Prob. 12RQCh. 12 - Prob. 13RQCh. 12 - Prob. 14RQCh. 12 - Prob. 15RQCh. 12 - Prob. 16RQCh. 12 - Prob. 1DQCh. 12 - Prob. 2DQCh. 12 - Prob. 1PCh. 12 - Prob. 2PCh. 12 - Prob. 3PCh. 12 - Prob. 4PCh. 12 - Prob. 5PCh. 12 - Prob. 6PCh. 12 - Prob. 7PCh. 12 - If the Sun is 4.6 billion years old, how many...Ch. 12 - Prob. 9PCh. 12 - Prob. 10PCh. 12 - Prob. 11PCh. 12 - Prob. 12PCh. 12 - Prob. 1LTLCh. 12 - Prob. 2LTL
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- The Milky Way galaxy has about 5 x 10⁹ solar masses of gas in total. If 13 solar masses of that gas is turned into stars each year, how many more years could the Milky Way keep up with such a star formation rate? years (Note for comparison that the age of the universe is about 13.5 billion years, which can be written 1.35e10 years. Also, the value given is in the ballpark of how much gas in the Milky Way is used to make new stars each year.)arrow_forwardStars form in the Milky Way at a rate of about 1 solar mass per year. At this rate, how long would it take for all the interstellar gas in the Milky Way to be turned into stars if there were no fresh gas coming in from outside? How does this compare to the estimated age of the universe, 14 billion years? What do you conclude from this?arrow_forwardHow does the presence of an active galactic nucleus in a starburst galaxy affect the starburst process?arrow_forward
- Suppose three stars lie in the disk of the Galaxy at distances of 20,000 light-years, 25,000 light-years, and 30,000 light-years from the galactic center, and suppose that right now all three are lined up in such a way that it is possible to draw a straight line through them and on to the center of the Galaxy. How will the relative positions of these three stars change with time? Assume that their orbits are all circular and lie in the plane of the disk.arrow_forwardA molecular cloud is about 1000 times denser than the average of the interstellar medium. Let’s compare this difference in densities to something more familiar. Air has a density of about 1 kg/m3, so something 1000 times denser than air would have a density of about 1000 kg/m3. How does this compare to the typical density of water? Of granite? (You can find figures for these densities on the internet.) Is the density difference between a molecular cloud and the interstellar medium larger or smaller than the density difference between air and water or granite?arrow_forwardLook back at Figure 6.18 of Cygnus A and read its caption again. The material in the giant lobes at the edges of the image had to have been ejected from the center at least how many years ago? Figure 6.18 Radio Image. This image has been constructed of radio observations at the Very Large Array of a galaxy called Cygnus A. Colors have been added to help the eye sort out regions of different radio intensities. Red regions are the most intense, blue the least. The visible galaxy would be a small dot in the center of the image. The radio image reveals jets of expelled material (more than 160,000 light-years long) on either side of the galaxy. (credit: NRAO/AUI)arrow_forward
- What evidence can you give that we live in a galaxy?arrow_forwardAssume that dark matter is uniformly distributed throughout the Milky Way, not just in the outer halo but also throughout the bulge and in the disk, where the solar system lives. How much dark matter would you expect there to be inside the solar system? Would you expect that to be easily detectable? Hint: For the radius of the Milky Way’s dark matter halo, use R=300,000 light-years; for the solar system’s radius, use 100 AU; and start by calculating the ratio of the two volumes.arrow_forwardSuppose the Sagittarius dwarf galaxy merges completely with the Milky Way and adds 150,000 stars to it. Estimate the percentage change in the mass of the Milky Way. Will this be enough mass to affect the orbit of the Sun around the galactic center? Assume that all of the Sagittarius galaxy’s stars end up in the nuclear bulge of the Milky Way Galaxy and explain your answer.arrow_forward
- Why does star formation occur primarily in the disk of the Galaxy?arrow_forwardUsing the information provided in Table 18.1, what is the average stellar density in our part of the Galaxy? Use only the true stars (types OM) and assume a spherical distribution with radius of 26 light-years. Stars within 21 Light-Years of the Sunarrow_forwardHow would the density inside a cold cloud (T=10K) compare with the density of the ultra-hot interstellar gas (T=106K) if they were in pressure equilibrium? (It takes a large cloud to be able to shield its interior from heating so that it can be at such a low temperature.) (Hint: In pressure equilibrium, the two regions must have nT equal, where n is the number of particles per unit volume and T is the temperature.) Which region do you think is more suitable for the creation of new stars? Why?arrow_forward
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