Astronomy Picture of the Day
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October 22, 1995
A Quasar - Galaxy Collision?
John Bahcall, Institute for Advanced Study.
In 1963 astronomers were astounded to discover that certain faint,
star-like objects have
very large redshifts.
The large redshifts imply that these objects, now known as
quasars (QUASi-stellAR objects),
lie near the edge of the observable Universe.
To be visible at such extreme distances of billions of light years,
emit tremendous amounts of energy. Where does the energy come from?
In the most widely accepted model, a quasar is the bright nucleus of
an active galaxy powered by a central, supermassive
This Hubble Space Telescope image shows
a quasar known as PKS 2349 (the star-like object
near the centre) and a galaxy (surrounding fuzzy patch), but
the quasar is not at the galaxy's centre! In fact, the
and quasar seem to be colliding or merging.
This and other recent HST observations
suggest that astronomers' standard ideas about quasars may be wrong.
Tomorrow's picture: Gamma-Ray Quasars
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