<< Chapter < Page Chapter >> Page >

Hubble and Black Holes: http://www.spacetelescope.org/videos/hubblecast43a/. Hubblecast on black holes and active galactic nuclei (9:10).

Monster Black Holes: https://www.youtube.com/watch?v=LN9oYjNKBm8. May 2013 lecture by Professor Chung-Pei Ma of the University of California, Berkeley; part of the Silicon Valley Astronomy Lecture Series (1:18:03).

Collaborative group activities

  1. When quasars were first discovered and the source of their great energy was unknown, some astronomers searched for evidence that quasars are much nearer to us than their redshifts imply. (That way, they would not have to produce so much energy to look as bright as they do.) One way was to find a “mismatched pair”—a quasar and a galaxy with different redshifts that lie in very nearly the same direction in the sky. Suppose you do find one and only one galaxy with a quasar very close by, and the redshift of the quasar is six times larger than that of the galaxy. Have your group discuss whether you could then conclude that the two objects are at the same distance and that redshift is not a reliable indicator of distance. Why? Suppose you found three such pairs, each with different mismatched redshifts? Suppose every galaxy has a nearby quasar with a different redshift. How would your answer change and why?
  2. Large ground-based telescopes typically can grant time to only one out of every four astronomers who apply for observing time. One prominent astronomer tried for several years to establish that the redshifts of quasars do not indicate their distances. At first, he was given time on the world’s largest telescope, but eventually it became clearer that quasars were just the centers of active galaxies and that their redshifts really did indicate distance. At that point, he was denied observing time by the committee of astronomers who reviewed such proposals. Suppose your group had been the committee. What decision would you have made? Why? (In general, what criteria should astronomers have for allowing astronomers whose views completely disagree with the prevailing opinion to be able to pursue their research?)
  3. Based on the information in this chapter and in Black Holes and Curved Spacetime , have your group discuss what it would be like near the event horizon of a supermassive black hole in a quasar or active galaxy. Make a list of all the reasons a trip to that region would not be good for your health. Be specific.
  4. Before we understood that the energy of quasars comes from supermassive black holes, astronomers were baffled by how such small regions could give off so much energy. A variety of models were suggested, some involving new physics or pretty “far out” ideas from current physics. Can your group come up with some areas of astronomy that you have studied in this course where we don’t yet have an explanation for something happening in the cosmos?

Thought questions

Suppose you observe a star-like object in the sky. How can you determine whether it is actually a star or a quasar?

Got questions? Get instant answers now!

Why don’t any of the methods for establishing distances to galaxies, described in Galaxies (other than Hubble’s law itself), work for quasars?

Got questions? Get instant answers now!

Questions & Answers

which planet orbits the closest?
Alastair Reply
What is the angle between Earth's equator and the Celestial equator? In the drawing they seem pretty similar. Thank you for this study resource.
Chuck Reply
Describe the spectrum of each of the following: starlight reflected by dust, a star behind invisible interstellar gas, and an emission nebula
shakila Reply
If the Oort cloud contains 1012 comets, and ten new comets are discovered coming close to the Sun each year, what percentage of the comets have been “used up” since the beginning of the solar system?
Day Reply
what is spectral type of sun
Akshat Reply
what everyone asking here? and who answers for them?
Shashi Reply
highest frequency wavelengh
Kathy Reply
may I know which Kingdom shows largest diversity
Arpita Reply
or students should post tough likely questions
Adepitan Reply
for example questions on demand functions and etc
Adepitan Reply
are there no ways we can get tough questions to answer
Adepitan Reply
What do you mean?
Amman Reply
excellent book bro.... keep it up.... if I find any query i will ask u.... thanks
rao Reply
Hi! I'm a bit confused, what is this
Sizakele Reply
They hsve new set of questions every time they test us. i do revision with the tutorials they give us answer extra questions from their moodle site but every time i write exams there will be few not even 10% of the questions are they. most of the time i guess. They give us three lectures who do not
Phumza Reply

Get the best Astronomy course in your pocket!

Source:  OpenStax, Astronomy. OpenStax CNX. Apr 12, 2017 Download for free at http://cnx.org/content/col11992/1.13
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Astronomy' conversation and receive update notifications?