TALK ABSTRACT:
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  In the 1980s, some "normal" galaxies were noticed to have abnormally
  luminous X-ray sources seemingly located in their galaxy centers,
  which beguiled astronomers into thinking that perhaps these galaxies
  were not "normal" after all.  Now, with higher-resolution X-ray cameras,
  we realize that these peculiar X-ray emitting beacons are not "nuclear"
  sources, but point-like objects located near the nucleus, or even located
  further out in the galaxy extremeties.  These sources are now known
  as Ultra-luminous X-ray sources, and we know them to be fairly common:
  on average, one source is present in every five galaxies.  Our Milky
  Way galaxy has none!  However, astronomers are still beguiled as to
  what monster lies within these objects.  I will discuss several of
  the popular ideas for how ULXs emit such high X-ray luminosities.