21ST CENTURY ASTR.:STARS..(LL)-PACKAGE
6th Edition
ISBN: 9780393448450
Author: Kay
Publisher: NORTON
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Chapter 20, Problem 27QP
To determine
The Large Magellanic Cloud and Small Magellanic Cloud look like detached pieces of the Milky Way.
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Which of the following statements best describes our galaxy, the Milky Way?
O A bulge dominated system, with little or no disk, approximately 27,000 light years across.
A disk 100,000 lightyears across filled with gas and stars, with a bulge of older stars in the galaxy centre.
A disk 27,000 light years across with a bulge of gas and newly formed stars in the galaxy centre.
O A spherical (elliptical) galaxy, 100,000 lightyears across, with no gas and no new stars.
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.)
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 20 Solutions
21ST CENTURY ASTR.:STARS..(LL)-PACKAGE
Ch. 20.1 - Prob. 20.1CYUCh. 20.2 - Prob. 20.2CYUCh. 20.3 - Prob. 20.3CYUCh. 20.4 - Prob. 20.4CYUCh. 20 - Prob. 1QPCh. 20 - Prob. 2QPCh. 20 - Prob. 3QPCh. 20 - Prob. 4QPCh. 20 - Prob. 5QPCh. 20 - Prob. 6QP
Ch. 20 - Prob. 7QPCh. 20 - Prob. 8QPCh. 20 - Prob. 9QPCh. 20 - Prob. 10QPCh. 20 - Prob. 11QPCh. 20 - Prob. 12QPCh. 20 - Prob. 13QPCh. 20 - Prob. 14QPCh. 20 - Prob. 15QPCh. 20 - Prob. 16QPCh. 20 - Prob. 17QPCh. 20 - Prob. 18QPCh. 20 - Prob. 19QPCh. 20 - Prob. 20QPCh. 20 - Prob. 21QPCh. 20 - Prob. 22QPCh. 20 - Prob. 23QPCh. 20 - Prob. 24QPCh. 20 - Prob. 25QPCh. 20 - Prob. 26QPCh. 20 - Prob. 27QPCh. 20 - Prob. 28QPCh. 20 - Prob. 29QPCh. 20 - Prob. 30QPCh. 20 - Prob. 31QPCh. 20 - Prob. 32QPCh. 20 - Prob. 33QPCh. 20 - Prob. 34QPCh. 20 - Prob. 35QPCh. 20 - Prob. 36QPCh. 20 - Prob. 37QPCh. 20 - Prob. 38QPCh. 20 - Prob. 39QPCh. 20 - Prob. 40QPCh. 20 - Prob. 41QPCh. 20 - Prob. 42QPCh. 20 - Prob. 43QPCh. 20 - Prob. 44QPCh. 20 - Prob. 45QP
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- A 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_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_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_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_forwardIf the sun is 4.6 billion years old, how many times has it orbited the Milky Way? (The sun is 8,300 pc from the cemetery of the Milky Way, and orbits the center at a speed of 225 km/s.) ______ timesarrow_forwardThe 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…arrow_forward
- The Tully-Fischer method relies on being able to relate the mass of a galaxy to its rotation velocity. Stars in the outer-most regions of the Milky Way galaxy, located at a distance of 50 kpc from the galactic centre, are observed to orbit at a speed vrot determine the mass in the Milky Way that lies interior to 50 kpc. Express your answer in units of the Solar mass. 250 km s-1. Using Kepler's 3rd Law,arrow_forwardAs we discussed, clouds are made of a great many small drops. Really - a great many. Imagine a liquid cloud that fills a volume of 1 km3. The clouds contains 100 drops per cubic centimeter; for the sake of argument assume that each is 10 microns (micrometers) in radius. A. How many drops does the cloud contain? Compare this to a big number - say, the number of stars in the galaxy. B. What mass of water does the cloud contain? Compare this to something big - elephants, trucks, that sort of thing. C. What fraction of the cloud volume is filled with condensed water? One way to approach this is to compare the density of the suspended liquid water to the density of the surrounding air. D. How many 1 mm drizzle drops could you make from all the cloud drops? E. How much energy was released when this water condensed from vapor to liquid? If the water condensed in 20 minutes (a reasonable lifetime for a small cloud), what was the (energy per time)? powerarrow_forwardThe telescope and CCD camera described in question 2 are scheduled to observe the star cluster M67 at 22:00 GMT on 02/03/2022. Using Stellarium, determine whether or not this is a good time to observe the cluster. Choose the answer below that best matches your conclusions. a. No - the cluster is not visible from London at this date and time. b. The cluster is visible but the full Moon is close by and so will interfere with the observations. c. The cluster is visible but is very close to the horizon and so will be difficult to observe. d. The cluster M67 is never visible in the sky from London so we should abandon any plans to observe it. e. Yes this is a good time to observe the cluster as it is well placed in the sky for viewing and the moon is not visible.arrow_forward
- The Milky Way grew through merging with many smaller galaxies. What are the observational signatures of this process? O The motion of old stars in the bulge and halo of our galaxy are randomly orientated, meaning they were formed from collisions of small, accreted, galaxies all on different paths. O The ordered motion of the bulge / halo stars means that they came from many objects. The random motions of stars in the disk means it was formed from collisions of small, accreted, galaxies. O The motion of young stars in the disk are all in the same direction, meaning they came in as seperate objects.arrow_forwardSuppose that stars were born at random times over the last 1010 years. The rate of star formation is simply the number of stars divided by 1010 years. The fraction of stars with detected extrasolar planets is at least 11 %. The rate of star formation can be multiplied by this fraction to find the rate planet formation. How often (in years) does a planetary system form in our galaxy? Assume the Milky Way contains 3 × 1011 stars.arrow_forwardA given star orbits the center of its galaxy at an average speed of v_star, at a distance of r_star from the center. The galaxy has 2 spiral arms, and the arms themselves orbit slower than the star -- at the same radius, they orbit at a speed of v_arm (in the same direction as the star). The galaxy's age is t_gal. In the history of this galaxy, how many times did this star cross through a spiral arm? Values: v_star = 200 km/s, r_star = 9 kpc, v_arms = 46 km/s, t_gal = 4 Gyrarrow_forward
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