Radio Galaxies, Quasars and other oddities

Radio Galaxies:


Two we have seen before
Centaurus A
M87 jet turns into intense radio source

Cygnus A appears to be double galaxy with radio emission coming from distant lobes
Brightest radio object in sky: took a long time to find optical counterpart, since it is a distant galaxy. Emission is synchrotron from electrons ejected from centre

Note jet
Nowhere near largest radio source!

Quasars:


Quasi-stellar (radio) source, QSS. Large number of radio sources could not be identified with known objects. were originally discovered by radio: 3C48 found near blue "star" (1960)

Position of 3C273 found v. accurately by lunar occultation, so could be identified with 13 mag. blue "star" with jet projecting from it
This shows the problem: it shows a galaxy (maybe 2) a quasar and a star. Which is which?

Credit: C. Steidel (Caltech), HST, NASA

3C 273 bright enough that it had been recorded on old plates: hadn't moved in sky, so must be distant.
  • Variable output (flickering over a few minutes, 3 mags. change over a year)
  • Optical and radio variability not related.
  • spectrum very odd,
  • huge redshifts,
  • massive power output ∼ 100 x large galaxy
  • SIze ∼ few light hours ∼ size of solar system

i.e. light output occurs from same size region as supergiant star, but energy ∼ 1010 larger

What are they?


Best Bet Model! Supermassive black hole, consuming 10-20 M₀/year Surrounding galaxy produces emission lines "Flickering" from stars falling into black hole

Hence expect following scenario:

Quasars very plentiful in early universe. We see Seyfert galaxies, which seem to be intermediate, so quasars evolve to Seyferts or radio galaxies as black hole consumes most of central core, and then to normal spiral as central core becomes used up

Gravitational lensing...

About 10000 quasars known, and each is very characteristic: red-shifts and spectrum are very distinct.

However several pairs which lie very close in sky: e.g. 0957 +561A & 0957 +561B are 6" apart in sky and have identical red-shifts. Note "fuzz" sticking out of lower one
Can be understood via radio image: massive galaxies will bend light
THis one is imaged 4 times (the Einstein cross) Can just see the galaxy

Credit & Copyright: J. Rhoads (STScI) et al., WIYN, AURA, NOAO, NSF


Should allow us to measure mass of intervening galaxy, but not easy in practice.

And finally amongst the wierdos

Gamma-ray bursters

Found originally by Vela satellite (designed to look for γ's from nuclear explosions). Can identify source by using timinng with various satellites

Bursts last 1/10 - 100s, no particular pattern

Problems: Could not be identified with any known object

Possibly collisions between stars in very distant galaxies, or some unusual form of supernova

Image Credit: S. Kulkarni, J. Bloom, P. Price, Caltech - NRAO GRB Collaboration
Before we can start asking the profound questions, we need to talk about the sizes of things again: how big is the universe?