21st Century Astronomy
6th Edition
ISBN: 9780393428063
Author: Kay
Publisher: NORTON
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Chapter 20, Problem 24QP
To determine
Astronomers use X-ray, infrared, and 21-cm radio observations to probe the centre of the galaxy.
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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…
You observe the H-alpha line of Hydrogen in a distant galaxy to have a wavelength of 918.4 nm. What is the radial velocity of the galaxy?
Chapter 20 Solutions
21st Century Astronomy
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 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_forwardGlobular clusters revolve around the Galaxy in highly elliptical orbits. Where would you expect the clusters to spend most of their time? (Think of Kepler’s laws.) At any given time, would you expect most globular clusters to be moving at high or low speeds with respect to the center of the Galaxy? Why? (If you would like to learn more about globular clusters, read Section 22.2 of the book, though it is not necessary to answer this question)arrow_forwardThe 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 = 250 km s−1. Using Kepler’s 3rd Law, determine the mass in the Milky Way that lies interior to 50 kpc. Express your answer in units of the Solar mass.arrow_forward
- You observe the H-alpha line of Hydrogen in a distant galaxy to have a wavelength of 754.4 nm. What is the radial velocity of the galaxy? Hint: The rest wavelength of H-alpha is 656 nm.arrow_forwardYou observe the H-beta line of Hydrogen in a distant galaxy to have a wavelength of 558.9 nm. What is the radial velocity of the galaxy?arrow_forwardAmong the globular clusters orbiting a distant galaxy, one is moving at 534 km/s and is located 14 kpc from the center of the galaxy. Assuming the globular cluster is located outside most of the mass of the galaxy, what is the mass of the galaxy? Convert your answer to solar masses. (Hint: Use the formula for circular velocity, Vc = GM r ; make sure you convert relevant quantities to units of meters, kilograms, and seconds. Note: 1 pc = 3.1 ✕ 1016 m.)arrow_forward
- You observe the H-alpha line of Hydrogen in a distant galaxy to have a wavelength of 754.4 nm. What is the radial velocity of the galaxy? Hint: The rest wavelength of H-alpha is 656 nm. I have to use the forumla mentioned in the photo I shared with this post.arrow_forwardAmong the globular clusters orbiting a distant galaxy, one is moving at 417 km/s and is located 16 kpc from the center of the galaxy. Assuming the globular cluster is located outside most of the mass of the galaxy, what is the mass of the galaxy? Convert your answer to solar masses. (Hint: Use the formula for circular velocity, V, = V GM ; make sure you convert relevant quantities to units of meters, kilograms, and seconds. Note: 1 pc = 3.1 x 1016 m.) solar masses (M.)arrow_forwardThe Sun orbits the center of the Galaxy in 225 million years at a distance of 26,000 light-years. Given that a3=(M1+M2)P2 , where a is the semimajor axis and P is the orbital period, what is the mass of the Galaxy within the Sun’s orbit?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_forwardThe center of a faint but active galaxy has magnitude 26. How much less bright does it look than the very faintest star that our eyes can see, roughly magnitude 6?arrow_forward
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