CONTACT:  Ray Villard, STScI            THURSDAY, MAY 19, 1994
          (410) 338-4514

                                   PRESS RELEASE NO.: STScI-PR94-22

          Dr. Christopher Burrows ESA/STScI
          (410) 338-4913



       HUBBLE FINDS MYSTERIOUS RING STRUCTURE AROUND SUPERNOVA 1987A


NASA's Hubble Space Telescope (HST) has obtained the best images
yet of a mysterious mirror- imaged pair of rings of glowing gas
that are encircling the site of the stellar explosion supernova
1987A. 

One possibility is that the two rings might be "painted" by a
high-energy beam of radiation or particles, like a spinning light-
show laser beam tracing circles on a screen.

The source of the radiation might be a previously unknown stellar
remnant that is a binary companion to the star that exploded in
1987. Images taken by Hubble show a dim object in the position of
the suspected source of the celestial light show. 

"The Hubble images of the rings are quite spectacular  and
unexpected," says Dr. Chris Burrows of the European Space Agency
and the Space Telescope Science Institute in Baltimore, Maryland. 
Burrows used Hubble's Wide Field Planetary Camera 2 to image the
rings in February 1994.

The striking Hubble picture actually shows three rings.  The
smaller "center" ring of the trio was seen previously.  The larger
pair of outer rings were also seen in ground-based images, but the
interpretation was not possible until the higher resolution Hubble
observations.

Though all of the rings probably are inclined to our view (so that
they appear to intersect), they probably are in three different
planes.  The small  bright ring lies in a plane containing the
supernova; the two rings lie in front and behind it. 

To create the beams illuminating the outer rings, the remnant would
need to be a compact object such as a black hole or neutron star
with a nearby companion.  Material falling from the companion onto
the compact object would be heated and blasted back into space
along two narrow jets, along with a beam of radiation.  As the
compact object spins it might wobble or precess about its axis,
like a child's top winding down. The twin beam would then trace out
great circles like jets of water from a spinning lawn sprinkler.

If the rings are caused by a jet, however, the beams are extremely
narrow (collimated to within one degree). This leads Burrows to
conclude: "This is an unprecedented and bizarre object.  We have
never seen anything behave like this before."

The jet model explains why the rings appear to be mirror imaged,
and why they appear to be symmetrical about a point offset from the
center of the explosion. 

Burrows got the idea for the beam explanation when he noticed that
where a ring appears brighter, an equally bright region appears on
opposite ring.  By connecting lines between the similar clumps on
opposite rings Burrows found a common center.  However, it is
offset from the heart of the supernova ejecta.  When Burrows did a
detailed inspection of the HST image, he found a dim object which
may be the source of the beam at the predicted location. The object
is about 1/3 light-year from the center of the supernova explosion.

>From previous HST observations and images at lower resolution taken
at ground-based observatories, astronomers had expected to see an
hourglass-shaped bubble being blown into space by the supernova's
progenitor star.  "The rings are probably on the surface of the
hourglass shape," says Burrows.
 
The hourglass was formed by a wind of slow-moving gas that was
ejected by the star when it was a red supergiant, and a much faster
wind of gas that followed during the subsequent blue supergiant
stage. The hourglass was produced by the fact that the stellar wind
from the red giant was denser in the equatorial plane of the star.
When the star reached the blue supergiant stage, the faster winds
tended to break out at the poles of the star. 

Energetic radiation from the supernova explosion illuminated the
dense gaseous material in the equatorial "waist" of the hourglass,
causing it to glow -- thus explaining the central bright ring. 
However, the two outer rings might be painted on the surface of the
hourglass by a very different process, by the beams from the
stellar remnant.

Further observations with HST will study any further changes that
might occur. In particular, if a remnant companion really exists,
it should collide with the supernova's expanding cloud of ejecta in
the mid 1990s.

The observations were led by Dr. Chris Burrows in collaboration
with the WFPC 2 Investigation Definition Team.  The supernova is
169,000 light years away, and lies in the dwarf galaxy called the
Large Magellanic Cloud, which can be seen from the southern
hemisphere.



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The Space Telescope Science Institute is operated by the Association of
Universities for Research in Astronomy, Inc. (AURA) 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 (ESA).