EMBARGOED UNTIL:   2:00 p.m. (EDT) May 30, 1996

CONTACT:  Don Savage
          NASA Headquarters, Washington, DC                                  
          (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)

PRESS RELEASE NO.: STScI-PR96-22


       HUBBLE ASTRONOMERS UNVEIL "CRAB NEBULA -- THE MOVIE"

     Probing the mysterious heart of the Crab Nebula, the tattered remains of
a stellar cataclysm witnessed more than 900 years ago, astronomers using
NASA's Hubble Space Telescope have found that the Crab is even more dynamic
than previously understood, based on a cosmic "movie" assembled from a series
of Hubble observations.

     The results promise to shed new light on a variety of high energy
phenomena in the universe, from nearby neutron stars to remote quasars.

     Though changes in most astronomical objects are barely perceptible over a
human lifetime, Hubble shows that the interior of the nebula "changes its
stripes" every few days,  according to Jeff Hester of Arizona State University
in Tempe, AZ, who leads the team of astronomers that took the Wide Field and
Planetary Camera 2 (WFPC2) images.

     "We took the images a few weeks apart because we knew that it might be
possible to observe slight differences in the Crab over a short time," said
Hester.  "But I don't think that any of us were prepared for what we saw."

     Though ground-based images of the Crab had shown subtle changes in the
nebula over months or years, the Hubble movie shows sharp wisp-like features
streaming away from the center of the nebula at half the speed of light.

     The powerhouse at the center of the nebula responsible for these changes
is a rapidly spinning neutron star -- the compact core of the exploded star. 
Only about six miles (10 kilometers) across, the neutron star would fit inside
a small town, "yet its small size belies its significance and the punch that
it packs," said Hester. 

     As the neutron star spins on its axis 30 times a second, its twin
searchlight beams sweep past the Earth, causing the neutron star to blink on
and off.  Because of this flickering, the neutron star is also called a
"pulsar."  In addition to the pulses, the neutron star's rapid rotation and
intense magnetic field act as an immense slingshot, accelerating subatomic
particles to close to the speed of light and flinging them off into space.

     In a dramatic series of images assembled over several months of
observation, Hubble shows what happens as this magnetic pulsar "wind" runs
into the body of the Crab Nebula.  The glowing, eerie shifting patterns of
light in the center of the Crab are created by electrons and positrons
(anti-matter electrons) as they spiral around magnetic field lines and radiate
away energy.  This lights up the interior volume of the nebula, which is more
than 10 light-years across.

     The Hubble team finds that material doesn't move away from the pulsar in
all directions, but instead is concentrated into two polar "jets" and a wind
moving out from the star's equator. 

     The most dynamical feature in the inner part of the Crab is the point
where one of the polar jets runs into the surrounding material forming a shock
front.  The shape and position of this feature shifts about so rapidly that
the astronomers describe it as a "dancing sprite," or "a cat on a hot plate." 
The equatorial wind appears as a series of wisp-like features that steepen,
brighten, then fade as they move away from the pulsar to well out into the
main body of the nebula.

     "Watching the wisps move outward through the nebula is a lot like
watching waves crashing on the beach -- except that in the Crab the waves are
a light-year long and are moving through space at half the speed of light,"
said Hester. "You don't learn about ocean waves by staring at a snapshot.  By
their nature waves on the ocean are ever-changing.  You learn about ocean
waves by sitting on the beach and watching as they roll ashore.  This Hubble
'movie' of the Crab is so significant because for the first time we are
watching as these 'waves' from the Crab come rolling in."

     The Crab Nebula, the result of a supernova explosion witnessed by Chinese
astronomers in 1054 AD, also is widely studied because it offers a unique
opportunity to study high energy astrophysical phenomena.  The physical
processes that are at work in the centers of distant active galaxies and
quasars are thought to be much like the processes at work in the center of the
Crab, only on a vastly larger scale.  "The difference is that while
astronomers may never truly 'see' into the very heart of an active galaxy, the
Crab allows the properties and behavior of high energy winds and jets to be
studied up close and personal," Hester said.

     "The Hubble results aren't the end of the story," Hester emphasized. 
"Rather, they are a piece of a larger puzzle.  For example, the jets seen
streaming away from the pulsar in the Hubble data are of particular interest
because they help explain two lobes of X-ray emission seen extending away from
the pulsar in images taken with the Einstein and ROSAT X-ray satellites."

     In addition to Hester and Paul Scowen of Arizona State University, other
members of the team responsible for this work include Ravi Sankrit of Arizona
State University, Curt Michel of Rice University, Jay Gallagher of the
University of Wisconsin at Madison, James Graham of the University of
California at Berkeley, and Alan Watson of New Mexico State University.

     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).

                             - end -

NOTE TO EDITORS:  Image files in GIF and JPEG format and captions may be
accessed on Internet via anonymous ftp from ftp.stsci.edu in /pubinfo:

PRC96-22a Crab Ground/HST (color)  gif/CrabC.gif            jpeg/CrabC.jpg
PRC96-22b Crab Sequence (B&W)      gif/CrabSeq.gif          jpeg/CrabSeq.jpg

Higher resolution digital versions (300dpi JPEG) of the release photographs
will be available temporarily in /pubinfo/hrtemp: 96-22a.jpg and 96-22b.jpg
(color) and 96-22abw.jpg and 96-22bbw.jpg (black/white).

GIF and JPEG images and captions are also available via World Wide Web at URL:
http://www.stsci.edu/pubinfo/PR/96/22.html, or via links in 
http://www.stsci.edu/pubinfo/Latest.html and
http://www.stsci.edu/pubinfo/Pictures.html.

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