1. Quasars and Active Galaxies
Chapter 16
Quasars and Active Galaxies

2. What do you think?
What do quasars look like?
What powers a quasar?

3. Galaxy Cygnus A
This galaxy has a red shift corresponding to 6% the speed of light or 750 million light-years away

4. Quasars look like stars but have huge redshifts
object with a spectrum much like a dim star
highly red shifted
enormous recessional velocity
huge distance (ala Hubble’s Law)
must be enormously bright to be visible at such a great distance
Quasi-stellar object
QSO or Quasar

5. This object that looks like a star must be enormously luminous - its redshift indicates it is 4 billion light years away!!

6. 3C 273’s spectral lines are greatly redshifted
This change implies a distance of 2 billion light years

7. A quasar emits a huge amount of energy from a small volume
Such rapid changes in brightness can only result from changes small objects

8. Active Galaxies bridge the energy gap between ordinary galaxies and quasars
peculiar galaxies (pec)
appear to be blowing themselves apart

10. Active Galaxies bridge the energy gap between ordinary galaxies and quasars
peculiar galaxies (pec)
appear to be blowing themselves apart
Seyfert galaxies
luminous, star-like nuclei with strong emission lines

12. Active Galaxies bridge the energy gap between ordinary galaxies and quasars
peculiar galaxies (pec)
appear to be blowing themselves apart
Seyfert galaxies
luminous, star-like nuclei with strong emission lines
BL Lacertae objects (BL Lacs)
featureless spectrum with a brightness that can vary by a factor of 15 times in a few months.

14. Radio image of Cygnus A showing a small but very bright radio galaxy in the middle of the 320,000 ly wide lobes

15. Active galaxies lie at the center of double radio sources

16. Supermassive black holes lurk at the centers of some galaxies
High resolution spectroscopy allows astronomers to peak at the motion of gas near centers of galaxies
Some galaxies exhibit high-velocity jets of material leaving the center
Observations suggest that the centers of some galaxies are incredibly massive
All of this suggests the existence of supermassive black holes

17. Giant Gas Clouds Intergalactic gas jet Galaxy (surrounding the galaxy)
(which is actually quite large)

18. Jets of matter ejected from around a black hole may explain quasars and active galaxies

19. Jets of matter ejected from around a black hole may explain quasars and active galaxies

20. From where you observe it might make all the difference ...

21. What did you think? What do quasars look like? What powers a quasar?
They look like stars but spew out immense energy
What powers a quasar?
A quasar is a galaxy powered by a supermassive black hole at its center.

22. Self-Check
1: Describe the observable properties of quasars and indicate how they are identified.
2: Explain why intrinsic properties of quasars are so difficult to explain.
3: List the various types of active galaxies and discuss how each might be related to quasars.
4: Discuss the observations that seem to be consistent with the presence of supermassive black holes in most galaxies.