Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

November 25, 1996

A Quasar Portrait Gallery
J. Bahcall (IAS, Princeton), M. Disney (Univ. Wales), NASA

Explanation: QUASARs (QUASi-stellAR objects) lie near the edge of the observable Universe. Discovered in 1963, astronomers were astounded - to be visible at such extreme distances of billions of light-years they must emit prodigious amounts of energy. Where does the energy come from? Many believe the quasar's central engine is a giant black hole fueled by tremendous amounts of infalling gas, dust, and stars. This recently released gallery of quasar portraits from the Hubble Space Telescope offers a look at their local neighbourhoods: the quasars themselves appear as the bright star-like objects with diffraction spikes. The images in the centre and right hand columns reveal quasars associated with disrupted colliding and merging galaxies which should provide plenty of debris to feed a hungry black hole. Yet, in the left hand column a quasar is seen at the centre of an otherwise normal looking spiral (above) and elliptical galaxy. Whatever the secret of the quasar's energy, all these sites must provide fuel for its central engine.

Tomorrow's picture: The Radio Sky: Tuned to 408MHz

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