Don Savage
Headquarters, Washington, DC                   		
	
Aug. 7, 1995
(Phone:  202/358-1547)

Tammy Jones
Goddard Space Flight Center, Greenbelt, Md.
(Phone:  301/286-5566)

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
(Phone:  410/338-4514)

RELEASE:  95-182 (133)

HUBBLE FINDS SURPRISINGLY COMPLEX STRUCTURES IN RADIO 
GALAXIES 
         Probing some of the most distant and energetic galaxies in the universe, NASA's 
Hubble Space Telescope has uncovered surprisingly varied and intricate structures of 
stars and gas that suggest the processes powering these so-called radio galaxies are more 
complex than previously thought.

         The Hubble observations, made by a team of astronomers at Cambridge University, 
England, should shed light on the nature of active galaxies that might be powered by 
immense black holes at their cores, and more generally, on galactic evolution.  The radio 
galaxies observed are so far away they existed when the universe was half its present age, 
and the light is only now reaching us.

         The bizarre, never-before-seen details may be a combination of light from massive 
star forming regions, small satellite dwarf galaxies, and bow shocks caused by jets of hot 
gas blasted out of the galaxy's core by a suspected black hole.

         The observations were made by Professor Malcolm Longair and Philip Best of the 
Cavendish Laboratory,Cambridge University, and Huub Rottgering of Leiden 
Observatory, The Netherlands, who have published images of three radio galaxies 
(3C368, 3C324 and 3C265) in the August 1 issue of the Monthly Notices of the Royal 
Astronomical 
Society. 
         The team is analyzing a sample of 28 radio galaxies that have been imaged by 
Hubble in visible light, by the Very Large Array Radio Interferometer (an array of 27 
separate radio antennas) at radio wavelengths, and by the UK Infrared Telescope.

         A radio galaxy emits powerful radio waves along two opposite directions pointing 
out from the galaxy's core.  The radio lobes usually extend far beyond the host galaxy.  
The suspected powerhouse behind the radio emission is a one-billion solar mass black 
hole in a galaxy's core.  Gaseous jets, traveling at nearly the speed of light, blast out along 
the rotation axis of the spinning black hole.  These jets bore through space like a narrow 
stream of water from a garden hose nozzle plowing through sand.  When they are finally 
stopped by the intergalactic medium, a huge amount of energy is released in the form of 
radio waves.

         Previous ground-based observations since 1987 have shown that, in visible light, 
radio galaxies have an unusual elongated structure -- unlike the classic spiral and 
elliptical shapes in normal galaxies -- that align to the twin lobe of radio emissions that 
are the trademark of such active galaxies.  In the Hubble views, these shapes break up 
into a string of bright knots that might be regions where new stars are forming, or could 
be glowing clouds of gas.  In one galaxy, the knots align to the axis of the jet, while in 
another case they do not, and instead cluster around the galaxy like smaller "satellite" 
galaxies.

         One explanation for the alignment between the invisible jets and optical structures is 
that the jets trigger the formation of stars along their paths.  However, some of the 
galaxies emit highly polarized light.  Since this type of light is not produced by stars, 
other processes must be at work.  A possible explanation is that the light from the galaxy's 
hidden active nucleus is scattered in our direction by dust or electrons.

         Longair, Best and Rottgering propose that the remarkable structures seen in the 
Hubble images are different manifestations of activity associated with radio galaxies.  
They conclude at least two mechanisms responsible for the alignment effect.  They also 
note that the period during which there is strong radio emission is quite short relative to 
the total lifetime of a galaxy, so different processes may dominate as the radio source 
ages.  They are planning further observations to determine the relative importance of the 
different effects.

         The Space Telescope Science Institute is operated by the Association of Universities 
for Research in Astronomy, Inc., for NASA, under contract with the Goddard Space 
Flight Center, Greenbelt, Md.  The Hubble Space Telescope is a project of international 
cooperation between NASA and the European Space Agency.
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