30 Nov 2000ASTR103, GMU, Dr. Correll1 Ch 16--Quasars and AGNs

30 Nov 2000ASTR103, GMU, Dr. Correll2 What do you think? What do quasars look like? What powers a quasar?

30 Nov 2000ASTR103, GMU, Dr. Correll3 Quasars Discovered 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 10 7 times that of a normal galaxy!

30 Nov 2000ASTR103, GMU, Dr. Correll4 Quasars optical radio

30 Nov 2000ASTR103, GMU, Dr. Correll5 Quasar Red Shifts

30 Nov 2000ASTR103, GMU, Dr. Correll6 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 2000ASTR103, GMU, Dr. Correll7 Seyfert Galaxy Example Ground based visible, HST visible, and x-ray reveal very localized central nucleus

30 Nov 2000ASTR103, GMU, Dr. Correll8 M87--Elliptical Galaxy Example 50 Million light years from Earth; 3 billion solar mass nucleus (supermassive black hole?)

30 Nov 2000ASTR103, GMU, Dr. Correll9 Supermassive Central Engines

30 Nov 2000ASTR103, GMU, Dr. Correll10 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 2000ASTR103, GMU, Dr. Correll11 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 2000ASTR103, GMU, Dr. Correll12 Gamma Ray Bursters 21-cm radiation –penetrates through the interstellar dust to reveal spiral structure

30 Nov 2000ASTR103, GMU, Dr. Correll13 Quasars, AGNs, etc--Summary

30 Nov 2000ASTR103, GMU, Dr. Correll14 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