This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Donald Savage
Headquarters, Washington           Feb. 27, 2003
(Phone: 202/358-1727)

Steve Roy
Marshall Space Flight Center, Huntsville, Ala.
(Phone: 256/544-6535)

Megan Watzke
Chandra X-ray Observatory Center, CfA, Cambridge, Mass.
(Phone: 617/496-7998)

RELEASE: 03-81

A COCOON FOUND INSIDE THE BLACK WIDOW'S WEB

     NASA's Chandra X-ray Observatory image of the mysterious "Black 
Widow" pulsar reveals the first direct evidence of an elongated cocoon 
of high-energy particles. (A pulsar is a rotating neutron star 
producing powerful beams of radiation that sweep like a searchlight.) 
This discovery shows this billion-year-old rejuvenated pulsar is an
extremely efficient generator of a high-speed flow of matter and 
antimatter particles.

Known officially as pulsar B1957+20, the Black Widow received its 
nickname because it is emitting intense high- energy radiation that is 
destroying its companion through evaporation. B1957+20, which 
completes one rotation every 1.6-thousandths of a second, belongs to a 
class of extremely rapidly rotating neutron stars called millisecond 
pulsars. 

The motion of B1957+20 through the galaxy, almost a million kilometers 
per hour, creates a bow shock wave visible to optical telescopes. The 
Chandra observation shows what cannot be seen in visible light: a 
second shock wave. This secondary shock wave is created from pressure 
that sweeps the wind back from the pulsar to form the cocoon of high-
energy particles, visible for the first time in the Chandra data.

"This is the first detection of a double-shock structure around a 
pulsar," said Benjamin Stappers, of the Dutch Organization for 
Research in Astronomy (ASTRON), lead author on a paper describing the 
research that will appear in the Feb. 28, 2003, issue of Science 
magazine. "It should enable astronomers to test theories of the 
dynamics of pulsar winds and their interaction with their 
environment," he said.

Scientists believe millisecond pulsars are very old neutron stars that 
have been spun up by accumulating material from their companions. The 
steady push of the infalling matter spins it much the same way as 
pushing on a merry-go-round makes it rotate faster.

The result is an object about 1.5 times as massive as the Sun, 10 
miles in diameter, rotating hundreds of times per second. The advanced 
age, very rapid rotation rate and relatively low magnetic field of 
millisecond pulsars put them in a totally separate class from young 
pulsars observed in the remnants of supernova explosions. 

"This star has had an incredible journey. It was born in a supernova 
explosion as a young and energetic pulsar, but after a few million 
years grew old and slow and faded from view," said Bryan Gaensler of 
the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., a 
coauthor of the paper. "Over the next few hundred million years, this 
dead pulsar had material dumped on it by its companion, and the
pulsar's magnetic field has been dramatically reduced. 

"This pulsar has been through hell, yet somehow it's still able to 
generate high-energy particles just like its younger brethren," 
continued Gaensler. The key is the rapid rotation of B1957+20. The 
Chandra result confirms the theory that even a relatively weakly 
magnetized neutron star can generate intense electromagnetic forces 
and accelerate particles to high energies to create a pulsar wind, if 
it is rotating rapidly enough.

Chandra's Advanced CCD Imaging Spectrometer observed B1957+20 for more 
than 40,000 seconds on June 21, 2001. Other members of the research 
team include Victoria Kaspi (McGill University, Montreal), Michiel van 
der Klis (University of Amsterdam, Netherlands) and Walter Lewin
(Massachusetts Institute of Technology, Cambridge).

NASA's Marshall Space Flight Center, Huntsville, Ala., manages the 
Chandra program. TRW, Inc., Redondo Beach, Calif., is the prime 
contractor for the spacecraft. The Smithsonian's Chandra X-ray Center 
controls science and flight operations from Cambridge, Mass., for the 
Office of Space Science at NASA Headquarters, Washington.

Images and additional information about this result are available on 
the Internet at: 

http://chandra.harvard.edu
and
http://chandra.nasa.gov

For more information about NASA on the Internet:  www.nasa.gov

                                 -end-
                                 * * *
 - End of File -
================

---