Path: santra!tut!draken!kth!enea!mcvax!uunet!lll-winken!ames!yee
From: yee@ames.arc.nasa.gov (Peter E. Yee)
Newsgroups: sci.space
Subject: Astronomers discover active stellar corpse (Forwarded)
Message-ID: <20599@ames.arc.nasa.gov>
Date: 12 Jan 89 22:29:37 GMT
Reply-To: yee@ames.arc.nasa.gov (Peter E. Yee)
Organization: NASA Ames Research Center, Moffett Field, CA
Lines: 93

Charles Redmond
Headquarters, Washington, D.C.                  January 11, 1989

Ray Villard
Space Telescope Science Institute, Baltimore, Md.


RELEASE:  89-3

ASTRONOMERS DISCOVER ACTIVE STELLAR CORPSE


     A group of astronomers has discovered evidence of vigorous 
activity in a white-dwarf star previously thought to be a stellar 
"corpse" incapable of such lively behavior.  This new and 
unexpected behavior may offer astronomers new insight into how 
stars are born, evolve and ultimately die.
 
     When stars like the sun exhaust their nuclear fuel, they end 
their lives as inert white dwarfs, compact objects about the size 
of the Earth.  Astronomers have long believed that white dwarfs 
are incapable of further evolution other than a gradual cooling 
off.
 
     The white-dwarf star, cataloged as 0950+139, lies at the 
center of a faint nebula called EGB 6 and is located about 1500 
light-years from Earth in the direction of the constellation 
Leo.  The nebula was formed an estimated 50,000 years ago when 
the star was in the red-giant stage, which occurs late in a 
star's evolution.  When red giants subsequently exhaust their 
nuclear fuel and "burn out," they contract to become white 
dwarfs.
 
     Astronomers commonly believe that white-dwarf stars mark the 
end of any further stellar activity other than a gradual cooling 
off over billions of years.  The researchers found, however, that 
0950+139 is surrounded by a glowing cloud of gas about the size 
of our own solar system.  The star apparently has very recently 
shed additional gas long after entering the white-dwarf stage.


     Howard E. Bond of the Space Telescope Science Institute, 
Baltimore, Md., James Liebert and T. Fleming of the University of 
Arizona, Richard Green of Kitt Peak National Observatory, J.B. 
Holberg and K. Kidder of the Lunar and Planetary Laboratory, and 
F. Wesemael of the University of Montreal, presented their 
findings today at the 173rd meeting of the American Astronomical 
Society, in Boston, Mass.  The research was supported by the 
National Aeronautics and Space Administration and by the National 
Science Foundation.
 
     These findings are based on spectroscopic observations of 
the star made at Palomar, Kitt Peak, and Steward Observatories, 
and by NASA's International Ultraviolet Explorer satellite.  "A 
spectrum like this, with unmistakable signs of a surrounding gas 
cloud has never been seen before in such a highly evolved star," 
says Bond. "My co-workers and I believe the gas indicates that 
the star has very recently undergone additional mass loss."
 
     One possible explanation is that the white dwarf is 
continually losing mass into space through some unknown 
mechanism.  "Such behavior," says Bond, "is unexpected once a 
star has become a white dwarf because of the tremendous 
gravitational force at the surface of a white dwarf."
 
     Another possibility is that nuclear-fusion processes re-
ignited below the white dwarf's surface, causing it to balloon 
back to the red-giant phase.  Most of the star then re-collapsed 
back into the white dwarf observed today, while the outer layers 
escaped to form the observed second shell of material around the 
star.
 
     "This re-birth as a 'born-again' red giant may only have 
lasted for a few years and could well have gone unnoticed by
astronomers," says Bond. 
 
     Recent theoretical studies by I. Iben and J. MacDonald at 
the University of Illinois have revealed a possible explanation 
for such unusual behavior.  Hydrogen may diffuse below the white 
dwarf's surface to mix with carbon rising up from the dwarf's 
interior, leading to re-ignition of nuclear fusion.  Because this 
diffusion process is extremely slow, a star could have existed as 
a white dwarf for some time until the re-kindling of nuclear 
fusion.

     The Space Telescope Science Institute is operated for NASA 
under a contract with the Goddard Space Flight Center, Greenbelt, 
MD., by AURA (the Association of Universities for Research in
Astronomy, Inc.).  It is located on the Johns Hopkins University
campus in Baltimore.

     The Hubble Space Telescope is a project of international 
cooperation between NASA and the European Space Agency.