Observing Projects
You cannot see a black hole with a telescope. Nevertheless, you might want to observe the visible companion of Cygnus X-1. The epoch 2000 coordinates of this ninth-magnitude star are R.A. = 19h 58.4m and Decl. = +35° 12′, which is quite near the bright star η (eta) Cygni. Compare what you see with the photograph in Figure 21-10.
Use the Starry Night™ program to investigate the X-ray source and probable black hole, Cygnus X-1. This region of space is one of the brightest in the sky at X-ray wavelengths. Click the Home button in the toolbar and then use the Find pane to center the field of view on Cygnus X-1. If Cygnus X-1 is below the horizon, allow the program to reset the time to when it can best be seen. Click the checkbox to the left of the listing for Cygnus X-1 to apply a label to this object. Use the Zoom controls to set the field of view to 100 degrees. (a) Use the Time controls in the toolbar to determine when Cygnus X-1 rises and sets on today’s date from your location. (b) Zoom in until you can see an object at the location indicated by the label. What apparent magnitude and radius does Starry Night™ give for this object (you can obtain this information from the HUD or by using the Show Info command from the contextual menu for this object)? Keeping in mind that the object that gives rise to this X-ray source is a black hole, to what must this apparent magnitude and radius refer? Explain.
Use the Starry Night™ program to examine in some detail the central regions of two galaxies that contain supermassive black holes at their centers. (a) The Milky Way is one such galaxy. Select Favourites > Explorations > Milky Way Centre to view our Galaxy from the equivalent of the center of a transparent Earth. The star HIP86919 is very closely aligned with the direction of the central core of the galaxy and can be used as a guide when viewing this region. You can brighten the appearance of the Milky Way by opening Options > Stars > Milky Way… and moving the Brightness slider to the far right in the Milky Way Options panel. The Time and Date, August 30, 2009, at 6:30 a.m., have been chosen when the Moon is crossing the Milky Way plane, thereby providing a convenient angular scale, about ½° in diameter, for comparison with Milky Way features. (Click on Options > Solar System > Planets-Moons… to display the Planets-Moons Options window and make sure that the Enlarge Moon Size at large FOVs box under Other is Off, and click OK.) You will notice that, at visible wavelengths, this central region of the Milky Way appears to be dark. What explanation can you give for this dark band across the galactic plane? Zoom in to a field of view of about 5° around the galactic center to examine the region surrounding the black hole using the highly penetrating X-rays detected by the Chandra X-ray Space Telescope. If necessary, open the Options pane, expand the Deep Space layer, click On the Chandra Images and move the slider to the right to display the image mosaic showing numerous hot and intense X-ray sources very close to the supermassive black hole. (Note that this image is slightly offset from the galactic center to avoid confusion.) (b) M87 is an active galaxy for which evidence is strong for the presence of a supermassive black hole at its center. Click Home to return to your sky and stop the advancement of time. Use the Find tab to center your view on M87, allowing the program to adjust the time to ensure that this object is in your sky. Open the Options pane, expand the Deep Space layer and click Off the Chandra and Hubble Images, leaving the Messier Objects displayed, and then Zoom in to a field of view about 1° wide to show this giant elliptical galaxy as seen from ground-based telescopes. (You can click on the Info tab and click on Description to read about this somewhat featureless but surprising elliptical galaxy.) In the Options > Deep Space panel, move the slider to the right for the Chandra X-ray image to see the structure of hot gases around M87. Finally, move the Hubble Images slider to the right to display the high-resolution Hubble Space Telescope image of the gas jet emanating from the black hole. Again, this image is displaced to the upper-right from the galactic center position by the program. Right-click over this square image, click Centre and then zoom in to a field of view of about 1 arcminute to see this spectacular jet as it interacts violently with the interstellar medium above the black hole. Comment on the suggestion that supermassive black holes were discovered only after relatively recent advances were made in telescope and detector technology.
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Collaborative Exercises
Using Einstein’s special theory of relativity, estimate (1) the length of your pencil or pen at constant speed at the speeds of a bicycle rider, a car traveling on the highway, and a commercial jet liner at cruising altitude; and (2) the speed of a light beam emitted by a spaceship traveling at 200,000 km/s toward another spaceship traveling at the same speed.