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Quasars & Active Galaxies
Ch 17
Quasar "quasistellar
radio source"
The are point sources
(look like stars) with
highly redshifted spectra,
implying great distance.
They appear fairly bright
from Earth, but are very
far away 2 10 billion
light years away.
This means they are
very luminous objects.
They are the most luminous continuous sources in the
universe.
But they vary in brightness over time scales as short as just a
few hours. This implies the size of a quasar is less than a
few "light hours" across, < ~ 100 AU across.
We have seen that quasars lie at the cores of distant
galaxies; for many quasars we can detect a fairly typical
galaxy surrounding the quasar.
Other Active Galaxies: Active galaxiesare galaxies that emit lots energy that is not from stars not black radiation. Much of the energy comes from their cores, or "active galactic nuclei" or AGN's.
Some particular types:
Seyfert Galaxies Spiral galaxies with bright, starlike nuclei and strong emission lines
Radio galaxies Ellipticals with strong emissions at radio wavelengths, often with "radio lobes," which resemble jets "shooting out" from the core of the galaxy. The lobes come from the AGN
Cosmology (Ch 18)
cosmology the study of the universe as a whole, especially its origin & development
Assumptions:
- Principle of mediocrity
- Homogeneous universe at large scales (> ~100 Mpc) the universe looks the same everywhere
- Isotropic universe at large scales the universe looks the same in every direction
#'s 2 & 3 together make up theCosmological Principle: the universe is homogeneous & isotropic. It implies there is no up/down, in/out, center/edge to the universe.
Observations that tell us about the universe as a whole :
I. The night sky is dark.
II. Hubble's Law The more distant a galaxy, the more its spectrum is redshifted.
III. The visible matter in the universe is roughly 3/4 H & 1/ He, with traces of other elements.
IV. Microwave Background Radiation (MBR) we observe blackbody radiation coming to us from all directions in space. It corresponds to an "object" at a temperature of 2.7 K (most intense energy comes in microwave wavelengths). The radiation is almost perfectly isotropic (variations are at the level of 1 part per 100,000, or ~ 0.0001 K). Was discovered by Penzias & Wilson of Bell Labs in
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