Download Lec12_ch16_quasarsagns

Ch 16--Quasars and AGNs
30 Nov 2000
ASTR103, GMU, Dr. Correll
1
What do you think?
• What do quasars look like?
• What powers a quasar?
30 Nov 2000
ASTR103, GMU, Dr. Correll
2
Quasars Discovered
• 1936--Amateur astronomer, Grote Reber, builds
the first radio telescope in his backyard. He find
several strong radio sources
– Sagittarius A--from the galactic nucleus
– Cassiopeia A--supernova remnant in our galaxy
– Cygnus A--unusual
• first optical measurements were in 1951, showing a strange
galaxy in the direction of the radio source
• red-shift indicated a distance of 690 million light years!
• The strong radio signal, at such a great distance,
indicates a luminosity about 107 times that of a
normal galaxy!
30 Nov 2000
ASTR103, GMU, Dr. Correll
3
Quasars
optical
radio
30 Nov 2000
ASTR103, GMU, Dr. Correll
4
Quasar Red Shifts
30 Nov 2000
ASTR103, GMU, Dr. Correll
5
Quasars, AGNs, etc
• Quasars--quasi stellar objects, the oldest (most
distant) and most energetic galaxies
• Active Galactic Nuclei--not as far away and not
as powerful as Quasars
– exhibit rapid variability--indicating small energy
sources (solar system size!)
– diverse spectra--some dominated by absorption, some
by emission, some featureless--classified by names
such as peculiar galaxies, seyfert galaxies, BL Lac
objects
– optical/xray emission near nucleus and extended radio
lobes
30 Nov 2000
ASTR103, GMU, Dr. Correll
6
Seyfert Galaxy Example
• Ground based visible,
HST visible, and x-ray
reveal very localized
central nucleus
30 Nov 2000
ASTR103, GMU, Dr. Correll
7
M87--Elliptical Galaxy Example
• 50 Million light years from Earth; 3 billion solar mass
nucleus (supermassive black hole?)
30 Nov 2000
ASTR103, GMU, Dr. Correll
8
Supermassive Central Engines
30 Nov 2000
ASTR103, GMU, Dr. Correll
9
Radio Maps of the Milky Way
• HST Images consistent with Supermassive black hole central
engine--billion solar masses within hundreds of ly nucleus
30 Nov 2000
ASTR103, GMU, Dr. Correll
10
Gamma Ray Bursters
• Gamma ray detectors on satellites have discovered that
many gamma ray burst sources occur.
• Recent observations confirm they are very energetic
and very distant--suspected that they are energized by
black hole engines, possibly capturing other black holes
or neutron stars
30 Nov 2000
ASTR103, GMU, Dr. Correll
11
Gamma Ray Bursters
• 21-cm radiation
– penetrates through the
interstellar dust to
reveal spiral structure
30 Nov 2000
ASTR103, GMU, Dr. Correll
12
Quasars, AGNs, etc--Summary
30 Nov 2000
ASTR103, GMU, Dr. Correll
13
What do you think?
• What do quasars look like?
– They look like stars, but they radiate many times more
energy than any star
• What powers a quasar?
– A quasar is believed to be powered by a supermassive
black hole at the center of the galaxy
30 Nov 2000
ASTR103, GMU, Dr. Correll
14